In which an attacker, having connected to a channel between counterparties, intervenes in the transmission protocol, deleting or distorting information.

Principle of attack

The attack usually begins with listening to the communication channel and ends with the fact that the cryptanalyst tries to replace the intercepted message, extract from it useful information, redirect it to some external resource.

Suppose object A plans to send some information to object B. Object C has knowledge about the structure and properties of the data transfer method used, as well as the fact that the planned transfer of the actual information that C plans to intercept. To carry out an attack, C “presents itself” to object A as B, and to object B as A. Object A, mistakenly believing that it is sending information to B, sends it to object C. Object C, having received the information and performing some actions with it (for example, , copying or modifying for their own purposes) sends the data to the recipient itself - B; object B, in turn, believes that the information was received by him directly from A.

Attack example

Injection of malicious code

A man-in-the-middle attack allows a cryptanalyst to inject his code into emails, SQL statements, and web pages (i.e., allows SQL injection, HTML/script injection, or XSS attacks), and even modify user-uploaded binaries in order to to access account user or change the behavior of a program downloaded by the user from the Internet.

Downgrade attack

The term "Downgrade Attack" refers to such an attack in which the cryptanalyst forces the user to use less secure functions, protocols that are still supported for compatibility reasons. This type of attack can be carried out on the SSH , IPsec and PPTP protocols.

To protect against a Downgrade Attack, insecure protocols must be disabled on at least one side; just supporting and using secure protocols by default is not enough!

SSH V1 instead of SSH V2

An attacker may try to change the connection parameters between the server and the client when a connection is established between them. According to a talk given at the Blackhat Conference Europe 2003, a cryptanalyst can "force" a client to start an SSH1 session instead of an SSH2 session by changing the version number "1.99" for the SSH session to "1.51", which means using ssh V1. The SSH-1 protocol has vulnerabilities that a cryptanalyst can exploit.

IPsec

In this attack scenario, the cryptanalyst misleads his victim into thinking that an IPsec session cannot start at the other end (server). This causes messages to be forwarded explicitly if the host machine is in rollback mode.

PPTP

At the stage of negotiating PPTP session parameters, the attacker can force the victim to use a less secure PAP authentication, MSCHAP V1 (that is, "roll back" from MSCHAP V2 to version 1), or not use encryption at all.

An attacker can force his victim to repeat the stage of negotiating the PPTP session parameters (send a Terminate-Ack packet), steal the password from the existing tunnel and repeat the attack.

Public means of communication without protection of the authenticity, confidentiality, availability and integrity of information

The most common means of communication in this group is social network, a public email service and instant messaging system. The owner of the resource that provides the communication service has full control over the information exchanged by the correspondents and, at his own discretion, can easily carry out an attack at any time.

Unlike previous scenarios based on the technical and technological aspects of communications, in this case the attack is based on mental aspects, namely, on the rooting in the minds of users of the concept of ignoring information security requirements.

Will encryption save?

Consider the case of a standard HTTP transaction. In this case, the attacker can quite easily break the original TCP connection into two new ones: one between himself and the client, the other between himself and the server. This is fairly easy to do, since very rarely the connection between the client and the server is direct, and in most cases they are connected through a number of intermediate servers. A MITM attack can be carried out on any of these servers.

However, if the client and server communicate over HTTPS - a protocol that supports encryption - a man-in-the-middle attack can also be carried out. With this type of connection, TLS or SSL is used to encrypt requests, which, it would seem, makes the channel secure from sniffing and MITM attacks. An attacker can create two independent SSL sessions for each TCP connection. The client establishes an SSL connection with the attacker, who in turn creates a connection with the server. The browser in such cases usually warns that the certificate is not signed by a trusted certificate authority, but ordinary users of older browsers can easily bypass this warning. In addition, an attacker may have a certificate signed by a root CA (for example, such certificates are sometimes used for DLP) and not generate warnings. In addition, there are a number of attacks on HTTPS. Thus, the HTTPS protocol cannot be considered secure from MITM attacks by ordinary users. [ ] There are a number of measures that prevent some of the MITM attacks on https sites, in particular, HSTS , which prohibits the use of http connections from sites, Certificate pinning and HTTP Public Key Pinning , which prohibit certificate substitution.

MITM attack detection

To detect a man-in-the-middle attack, network traffic must be analyzed. For example, to detect an SSL attack, you should pay attention to the following parameters:

• Server IP
• DNS server
• X.509 server certificate
  • Is the certificate self-signed?
  • Is the certificate signed by a certificate authority?
  • Has the certificate been revoked?
  • Has the certificate changed recently?
  • Have other clients on the Internet received the same certificate?

MITM attack implementations

The listed programs can be used to carry out man-in-the-middle attacks, as well as to detect them and test the system for vulnerabilities.

see also

• Aspidistra (English) - British radio transmitter used during World War II "invasions", a variant of the MITM attack.
• The Babington Plot (English) - a conspiracy against Elizabeth I, during which Walsingham intercepted correspondence.

Other attacks

• Man in the Browser is a type of attack in which an attacker is able to instantly change transaction parameters, change pages completely transparently to the victim.
• "Meet-in-the-middle attack" - a cryptographic attack that, like the birthday attack, uses a trade-off between time and memory.
• "Loss in the middle" (Miss in the middle attack) is an effective method of the so-called impossible differential cryptanalysis.
• Relay attack - A variant of a MITM attack based on forwarding an intercepted message to a valid recipient, but not to the intended recipient.
• A rootkit is a program designed to hide traces of the presence of an intruder.

Write a review on the article "Attack of the intermediary"

Literature

Links

• www.all.net/CID/Attack/Attack74.html
• www.nag.ru/2003/0405/0405.shtml
• www.schneier.com/blog/archives/2006/04/rfid_cards_and.html

An excerpt characterizing the attack of the middleman

“Quartire, quartire, logement,” said the officer, looking down at the little man with a condescending and good-natured smile. – Les Francais sont de bons enfants. Que diable! Voyons! Ne nous fachons pas, mon vieux, [Apartments, apartments… The French are good guys. Damn it, let's not quarrel, grandfather.] - he added, patting the frightened and silent Gerasim on the shoulder.
– A ca! Dites donc, on ne parle donc pas francais dans cette boutique? [Well, doesn't anyone speak French here, too?] he added, looking around and meeting Pierre's eyes. Pierre moved away from the door.
The officer again turned to Gerasim. He demanded that Gerasim show him the rooms in the house.
"No master - don't understand... my yours..." said Gerasim, trying to make his words clearer by speaking them backwards.
The French officer, smiling, spread his hands in front of Gerasim's nose, making it feel that he did not understand him either, and, limping, went to the door where Pierre was standing. Pierre wanted to move away in order to hide from him, but at that very moment he saw Makar Alekseich leaning out of the kitchen door opening with a pistol in his hands. With the cunning of a madman, Makar Alekseevich looked at the Frenchman and, raising his pistol, took aim.
- Aboard!!! - the drunk shouted, pressing the trigger of the pistol. The French officer turned around at the cry, and at the same moment Pierre rushed at the drunk. While Pierre grabbed and raised the pistol, Makar Alekseich finally hit the trigger with his finger, and a shot rang out that deafened and doused everyone with powder smoke. The Frenchman turned pale and rushed back to the door.
Having forgotten his intention not to reveal his knowledge of the French language, Pierre, snatching the pistol and throwing it away, ran up to the officer and spoke to him in French.
- Vous n "etes pas blesse? [Are you injured?] - he said.
“Je crois que non,” the officer answered, feeling himself, “mais je l "ai manque belle cette fois ci,” he added, pointing to the chipped plaster in the wall. “Quel est cet homme? [It seems not ... but this once it was close. Who is this man?] - looking sternly at Pierre, the officer said.
- Ah, je suis vraiment au desespoir de ce qui vient d "arriver, [Ah, I really am in despair over what happened,] - Pierre said quickly, completely forgetting his role. - C" est un fou, un malheureux qui ne savait pas ce qu "il faisait. [This is an unfortunate madman who did not know what he was doing.]
The officer went up to Makar Alekseevich and seized him by the collar.
Makar Alekseich, with parted lips, as if falling asleep, swayed, leaning against the wall.
“Brigand, tu me la payeras,” said the Frenchman, withdrawing his hand.
– Nous autres nous sommes clements apres la victoire: mais nous ne pardonnons pas aux traitres, [Robber, you will pay me for this. Our brother is merciful after the victory, but we do not forgive the traitors,] he added with gloomy solemnity in his face and with a beautiful energetic gesture.
Pierre continued to persuade the officer in French not to exact from this drunken, insane man. The Frenchman listened in silence, without changing his gloomy look, and suddenly turned to Pierre with a smile. He looked at him silently for a few seconds. His handsome face took on a tragically tender expression, and he held out his hand.
- Vous m "avez sauve la vie! Vous etes Francais, [You saved my life. You are a Frenchman,]" he said. For a Frenchman, this conclusion was undeniable. Only a Frenchman could do a great deed, and saving his life, m r Ramball "I capitaine du 13 me leger [Monsieur Rambal, captain of the 13th light regiment] was, without a doubt, the greatest deed.
But no matter how undoubted this conclusion and the officer’s conviction based on it, Pierre considered it necessary to disappoint him.
“Je suis Russe, [I am Russian],” Pierre said quickly.
- Ti ti ti, a d "autres, [tell it to others] - said the Frenchman, waving his finger in front of his nose and smiling. - Tout a l "heure vous allez me conter tout ca," he said. – Charme de rencontrer un compatriote. Eh bien! qu "allons nous faire de cet homme? [Now you will tell me all this. It is very nice to meet a compatriot. Well! what should we do with this man?] - he added, addressing Pierre, already as his brother. If only Pierre was not a Frenchman, having once received this highest title in the world, he could not renounce it, said the expression on the face and tone of the French officer. To the last question, Pierre once again explained who Makar Alekseich was, explained that just before their arrival this a drunken, insane man dragged away a loaded pistol, which they did not have time to take away from him, and asked that his deed be left without punishment.
The Frenchman stuck out his chest and made a royal gesture with his hand.
- Vous m "avez sauve la vie. Vous etes Francais. Vous me demandez sa grace? Je vous l" accorde. Qu "on emmene cet homme, [You saved my life. You are a Frenchman. Do you want me to forgive him? I forgive him. Take this man away,] the French officer said quickly and energetically, taking by the arm what he had produced for saving his life into Pierre's French, and went with him to the house.
The soldiers who were in the yard, hearing the shot, went into the passage, asking what had happened, and expressing their readiness to punish the guilty; but the officer severely stopped them.
“On vous demandera quand on aura besoin de vous, [When needed, you will be called,” he said. The soldiers left. The batman, who had meanwhile been in the kitchen, approached the officer.
“Capitaine, ils ont de la soupe et du gigot de mouton dans la cuisine,” he said. - Faut il vous l "apporter? [The captain has soup and roast lamb in the kitchen. Would you like to bring it?]
- Oui, et le vin, [Yes, and wine,] - said the captain.

The French officer, together with Pierre, entered the house. Pierre considered it his duty to assure the captain again that he was not a Frenchman, and wanted to leave, but the French officer did not want to hear about it. He was so courteous, amiable, good-natured and truly grateful for saving his life that Pierre did not have the courage to refuse him and sat down with him in the hall, in the first room into which they entered. To Pierre's assertion that he was not a Frenchman, the captain, obviously not understanding how it was possible to refuse such a flattering title, shrugged his shoulders and said that if he certainly wants to be known as a Russian, then so be it, but that he, despite then, all the same forever connected with him by a feeling of gratitude for saving a life.
If this person had been gifted with at least some ability to understand the feelings of others and had guessed about Pierre's feelings, Pierre would probably have left him; but the lively impenetrability of this man to everything that was not himself defeated Pierre.
- Francais ou prince russe incognito, [Frenchman or Russian prince incognito,] - said the Frenchman, looking at Pierre's dirty, but thin underwear and the ring on his hand. - Je vous dois la vie je vous offre mon amitie. Un Francais n "oublie jamais ni une insulte ni un service. Je vous offre mon amitie. Je ne vous dis que ca. [I owe you my life, and I offer you friendship. A Frenchman never forgets insults or services. I offer my friendship to you, I say no more.]
In the sounds of his voice, in the expression of his face, in the gestures of this officer, there was so much good nature and nobility (in the French sense) that Pierre, responding with an unconscious smile to the smile of the Frenchman, shook the outstretched hand.
- Capitaine Ramball du treizieme leger, decore pour l "affaire du Sept, [Captain Ramball, thirteenth light regiment, cavalier of the Legion of Honor for the cause of the seventh of September,] - he introduced himself with a smug, uncontrollable smile that wrinkled his lips under his mustache. - Voudrez vous bien me dire a present, a qui "j" ai l "honneur de parler aussi agreablement au lieu de rester a l" ambulance avec la balle de ce fou dans le corps. [Will you be so kind as to tell me now who I am with I have the honor of talking so pleasantly, instead of being at the dressing station with this madman's bullet in his body?]
Pierre answered that he could not say his name, and, blushing, began, trying to invent a name, to talk about the reasons why he could not say this, but the Frenchman hastily interrupted him.
“De grace,” he said. - Je comprends vos raisons, vous etes officier ... officier superieur, peut etre. Vous avez porte les armes contre nous. Ce n "est pas mon affaire. Je vous dois la vie. Cela me suffit. Je suis tout a vous. Vous etes gentilhomme? [Complete, please. I understand you, you are an officer ... a staff officer, maybe. You served against us It's none of my business. I owe you my life. That's enough for me, and I'm all yours. Are you a nobleman?] - he added with a hint of a question. Pierre tilted his head. - Votre nom de bapteme, s "il vous plait? Je ne demande pas davantage. Monsieur Pierre, dites vous… Parfait. C "est tout ce que je desire savoir. [Your name? I don't ask anything else. Mr. Pierre, did you say? Fine. That's all I need.]
When roast lamb, scrambled eggs, a samovar, vodka and wine from a Russian cellar, which the French had brought with them, were brought, Ramball asked Pierre to take part in this dinner and immediately, eagerly and quickly, like a healthy and hungry man, began to eat, chewing quickly with his strong teeth, constantly smacking his lips and saying excellent, exquis! [wonderful, excellent!] His face was flushed and covered with sweat. Pierre was hungry and gladly took part in the dinner. Morel, the orderly, brought a pot of warm water and put a bottle of red wine in it. In addition, he brought a bottle of kvass, which he took from the kitchen for testing. This drink was already known to the French and got the name. They called the kvass limonade de cochon (pork lemonade), and Morel praised this limonade de cochon he found in the kitchen. But since the captain had wine obtained during the passage through Moscow, he provided kvass to Morel and took up a bottle of Bordeaux. He wrapped the bottle up to the neck in a napkin and poured himself and Pierre wine. The satisfaction of hunger and wine enlivened the captain still more, and he did not stop talking during dinner.
- Oui, mon cher monsieur Pierre, je vous dois une fiere chandelle de m "avoir sauve ... de cet enrage ... J" en ai assez, voyez vous, de balles dans le corps. En voila une (on pointed to his side) a Wagram et de deux a Smolensk, - he showed the scar that was on his cheek. - Et cette jambe, comme vous voyez, qui ne veut pas marcher. C "est a la grande bataille du 7 a la Moskowa que j" ai recu ca. Sacre dieu, c "etait beau. Il fallait voir ca, c" etait un deluge de feu. Vous nous avez taille une rude besogne; vous pouvez vous en vanter, nom d "un petit bonhomme. Et, ma parole, malgre l" atoux que j "y ai gagne, je serais pret a recommencer. Je plains ceux qui n" ont pas vu ca. [Yes, my dear Mr. Pierre, I am obliged to light a good candle for you for saving me from this madman. You see, I've had enough of the bullets that I have in my body. Here is one near Wagram, the other near Smolensk. And this leg, you see, that doesn't want to move. This is during the big battle of the 7th near Moscow. O! it was wonderful! You should have seen it, it was a deluge of fire. You have given us a hard job, you can boast. And by God, despite this trump card (he pointed to the cross), I would be ready to start all over again. I pity those who did not see it.]
- J "y ai ete, [I was there] - said Pierre.
- Bah, vraiment! Eh bien, tant mieux, said the Frenchman. - Vous etes de fiers ennemis, tout de meme. La grande redoute a ete tenace, nom d "une pipe. Et vous nous l" avez fait cranement payer. J "y suis alle trois fois, tel que vous me voyez. Trois fois nous etions sur les canons et trois fois on nous a culbute et comme des capucins de cartes. Oh!! c" etait beau, monsieur Pierre. Vos grenadiers ont ete superbes, tonnerre de Dieu. Je les ai vu six fois de suite serrer les rangs, et marcher comme a une revue. Les beaux hommes! Notre roi de Naples, qui s "y connait a crie: bravo! Ah, ah! soldat comme nous autres! - he said, smiling, ate a moment of silence. - Tant mieux, tant mieux, monsieur Pierre. Terribles en bataille ... galants ... - he winked with a smile, - avec les belles, voila les Francais, monsieur Pierre, n "est ce pas? [Ba, really? All the better. You are dashing enemies, I must admit. The big redoubt held up well, dammit. And you made us pay dearly. I've been there three times, as you can see. Three times we were on the cannons, three times we were knocked over like card soldiers. Your grenadiers were great, by God. I saw how their ranks closed six times and how they marched exactly to the parade. Wonderful people! Our Neapolitan king, who ate the dog in these cases, shouted to them: bravo! - Ha, ha, so you are our brother soldier! “So much the better, so much the better, Monsieur Pierre. Terrible in battle, kind to beauties, here are the French, Monsieur Pierre. Is not it?]
To such an extent, the captain was naively and good-naturedly cheerful, and wholehearted, and pleased with himself, that Pierre almost winked himself, looking at him cheerfully. Probably, the word "galant" made the captain think about the position of Moscow.

In this article, we will try to figure out the theory of man-in-the-middle attacks and some practical points that will help prevent these types of attacks. This will help us understand the risk that such intrusions pose to our privacy, as MitM attacks allow us to intrude on communications and listen in on our conversations.

Understanding how the internet works

To understand the man-in-the-middle attack, you must first understand how the Internet itself works. The main points of interaction: clients, routers, servers. The most common communication protocol between a client and a server is the Hypertext Transfer Protocol (HTTP). Web surfing with a browser, e-mail, instant messaging - all done through HTTP.

When you type in your browser's address bar, the client (you) sends a request to display a web page to the server. The packet (HTTP GET request) is sent through multiple routers to the server. The server then responds with a web page that is sent to the client and displayed on its monitor. HTTP messages must be transmitted in secure mode to ensure confidentiality and anonymity.

Figure 1. Client-server interaction

Securing the communication protocol

A secure communication protocol must have each of the following properties:

1. privacy- Only the intended recipient can read the message.
2. Authenticity- the identity of the interacting parties is proven.
3. Integrity- confirmation that the message has not been modified in transit.

If at least one of these rules is not followed, the entire protocol is compromised.

Man-in-the-middle attack over HTTP protocol

An attacker can easily carry out a man-in-the-middle attack using a technique called ARP spoofing. Anyone on your Wi-Fi network can send you a fake ARP packet, causing you to unknowingly send all your traffic through an attacker instead of a router.

After that, the attacker takes full control over the traffic and can monitor requests sent in both directions.

Figure 2. Man-in-the-middle attack scheme

To prevent such attacks, a secure version of the HTTP protocol was created. Transport Layer Security (TLS) and its predecessor, Secure Socket Layer (SSL), are cryptographic protocols that provide secure communication over a network. Hence, the secure protocol will be called HTTPS. You can see how the secure protocol works by typing in the address bar of your browser (note the S in https).

Man-in-the-middle attack on poorly implemented SSL

Modern SSL uses a good encryption algorithm, but it doesn't matter if it's not implemented correctly. If a hacker can intercept the request, they can change it by removing the "S" from the requested URL, thereby bypassing SSL.

Such interception and modification of the request can be noticed. For example, if you request https://login.yahoo.com/ and the response is http://login.yahoo.com/ , this should raise suspicion. At the time of writing, such an attack actually works on the Yahoo email service.

Figure 3. Intercepting and modifying a request

To prevent such an attack, servers can implement HTTP Strict Transport Security (HSTS), a mechanism that enforces a forced secure connection over the HTTPS protocol. In this case, if an attacker modifies the request by removing the “S” from the URL, the server will still redirect the user with a 302 redirect to a page with a secure protocol.

Figure 4. Scheme of HSTS operation

This way of implementing SSL is vulnerable to another type of attack - the attacker creates an SSL connection to the server, but tricks the user into using HTTP.

Figure 5. Attack scheme for HSTS

To prevent such attacks, modern browsers like Chrome, Firefox, and Tor monitor sites that use HSTS and enforce a client-side SSL connection with them. In this case, an attacker conducting a man-in-the-middle attack will have to create an SSL connection with the victim.

Figure 6. Scheme of the attack, where the attacker establishes an SSL connection with the victim

In order to secure an SLL connection to a user, an attacker must know how to act as a server. Let's understand the technical aspects of SSL.

Understanding SSL

From a hacker's point of view, compromising any communication protocol comes down to finding a weak link among the components listed above (privacy, authenticity, and integrity).

SSL uses an asymmetric encryption algorithm. In symmetric encryption, the problem is that the same key is used to encrypt and decrypt data, this approach is not acceptable for Internet protocols, since an attacker can trace this key.

Asymmetric encryption, on the other hand, involves 2 keys for each side: the public key used to encrypt and the private key used to decrypt the data.

Figure 7. Work of public and private keys

How does SSL provide the three properties required for secure communications?

1. Since asymmetric cryptography is used to encrypt data, SSL provides a private connection. This encryption is not so easy to crack and go unnoticed.
2. The server proves its legitimacy by sending the client an SSL certificate issued by a certificate authority, a trusted third party.

If an attacker somehow manages to get hold of the certificate, he can create the conditions for a man-in-the-middle attack. Thus, it will create 2 connections - with the server and with the victim. The server in this case thinks that the attacker is a normal client, and the victim has no way to identify the attacker, since he provided a certificate proving that he is a server.

Your messages reach and arrive in encrypted form, but pass along the chain through the cybercriminal's computer, where he has complete control.

Figure 8. Scheme of the attack if the attacker has a certificate

The certificate need not be forged if the attacker has the ability to compromise the victim's browser. In this case, it can insert a self-signed certificate that will be trusted by default. This is how most man-in-the-middle attacks are implemented. In more complex cases, the hacker must go the other way - forge the certificate.

Problems of certificate authorities

The certificate sent by the server is issued and signed by a certificate authority. Each browser has a list of trusted CAs and you can add or remove them. The problem here is that if you decide to remove the large authorities, you will not be able to visit sites that use certificates signed by these authorities.

Certificates and CAs have always been the weakest link in an HTTPS connection. Even if everything was implemented correctly and each certificate authority has a solid authority, it is still difficult to come to terms with the fact that you have to trust many third parties.

Today there are more than 650 organizations capable of issuing certificates. If an attacker hacks any of them, he will get any certificates he wants.

Even when there was only one certificate authority, VeriSign, there was a problem - the people who were supposed to prevent man-in-the-middle attacks were selling interception services.

Also, many certificates were created by hacking certificate authorities. Various techniques and tricks have been used to force the attacked user to trust fraudulent certificates.

Criminalistics

Because the attacker sends fake ARP packets, you can't see his IP address. Instead, you need to pay attention to the MAC address, which is specific to each device on the network. If you know your router's MAC address, you can compare it to the default gateway's MAC address to find out if it's really your router or an intruder.

For example, on Windows, you can use the ipconfig command in the command line (CMD) to see the IP address of your default gateway (last line):

Figure 9 Using the ipconfig command

Then use the arp -a command to find out the MAC address of this gateway:

Figure 10. Using the arp –a command

But there is another way to notice an attack - if you were monitoring the network activity at the time it started and watching the ARP packets. For example, you can use Wireshark for this purpose, this program will notify you if the MAC address of the default gateway has changed.

Note: If an attacker correctly spoofs MAC addresses, it will become a big problem to trace him.

Conclusion

SSL is a protocol that forces an attacker to do a lot of work to carry out an attack. But it won't protect you from government-sponsored attacks or qualified hacker organizations.

The task of the user is to protect their browser and computer in order to prevent the insertion of a fake certificate (a very common technique). You should also pay attention to the list of trusted certificates and remove those you do not trust.

10/18/2016 | Vladimir Khazov

The plans of the FSB, the Ministry of Telecom and Mass Communications and the Ministry of Industry and Trade to implement the provisions of the Yarovaya Law in terms of intercepting and decrypting the correspondence of Russians are no longer just plans, but are already beginning to be put into action by an order to prepare an expert opinion on the possibility of intercepting WhatsApp, Viber, Facebook Messenger, Telegram, Skype messages using MITM attacks and demonstration of a prototype of such a tool.

We wrote about the scheme for organizing a "legitimate" MITM attack in a previous article. Today we will dwell in more detail on the very principle of such an attack and how to implement it.

What is a MITM attack

Man In The Middle (MITM) translates as "man in the middle." This term refers to a network attack, when an attacker is between an Internet user and the application that he accesses. Not physically, of course, but with the help of special software. It is presented to the user by the requested application (it can be a website or an Internet service), imitates work with it, does it in such a way that it gives the impression of normal operation and information exchange.

The target of the attack is the user's personal data, such as login credentials to various systems, bank details and card numbers, personal correspondence and other confidential information. In most cases, financial applications (bank clients, online banks, payment and money transfer services), company SaaS services, e-commerce sites (online stores) and other sites where authorization is required to enter the system are attacked.

Information obtained by an attacker can be used for various purposes, including illegal money transfers, account switching, interception of personal correspondence, buying at someone else's expense, compromising and blackmail.

In addition, after stealing credentials and hacking into the system, criminals can install in corporate network malicious software for organizing the theft of intellectual property (patents, projects, databases) and causing economic damage by deleting important data.

A MITM attack can be compared to a postman who, during the delivery of your correspondence, opens the letter, rewrites its contents for personal use, or even, by forging handwriting, adds something of his own, and then seals the envelope and delivers it to the addressee as if nothing had happened . Moreover, if you encrypted the text of the letter, and you want to personally inform the addressee of the decryption code, the postman will present himself as the addressee so that you will not even notice the substitution.

How a MITM attack is carried out

The execution of a MITM attack consists of two phases: interception and decryption.

• Interception

The first stage of the attack is to intercept traffic from the user to the intended target and direct it to the attacker's network.

The most common and easiest way to intercept is a passive attack, when an attacker creates Wi-Fi points with free access (without password and authorization). At the moment when a user connects to such a point, the attacker has access to all traffic passing through it, and can extract any data from it for interception.

The second method is active interception, which can be carried out by one of the following options:

IP spoofing– substitution of the target IP address in the packet header with the address of the attacker. As a result, users, instead of going to the requested URL, end up on the attacker's site.

ARP spoofing– substitution of the host's real MAC address with the attacker's address in the victim's ARP table. As a result, the data sent by the user to the IP address of the required node gets to the address of the attacker.

DNS spoofing - infecting the DNS cache, infiltrating the DNS server, and spoofing the match record of the website address. As a result, the user tries to access the requested site, but receives the attacker's site address from the DNS server.

• Decryption

After interception, two-way SSL traffic must be decrypted, and this must be done in such a way that the user and the resource requested by him do not notice the interference.

There are several methods for this:

HTTPS spoofing– a fake certificate is sent to the victim's browser when a connection to the site is established via the HTTPS protocol. This certificate contains the digital signature of the compromised application, which causes the browser to accept the connection with the attacker as trusted. Once such a connection is established, the attacker has access to any data entered by the victim before it is passed to the application.

SSL BEAST(browser exploit against SSL/TLS) – the attack exploits an SSL vulnerability in TLS versions 1.0 and 1.2. The victim's computer is infected with malicious JavaScript that intercepts encrypted cookies sent to the web application. This compromises the "ciphertext block chaining" encryption mode in such a way that the attacker gets the decrypted cookies and authentication keys.

SSL hijacking– transmission of fake authentication keys to the user and application at the time of the start of the TCP session. This gives the appearance of a secure connection, when in fact the "man in the middle" is in control of the session.

SSL stripping- Downgrades the connection from secure HTTPS to plain HTTP by intercepting the TLS authentication sent by the application to the user. The attacker provides the user with unencrypted access to the site, while he himself maintains a secure session with the application, gaining the opportunity to see the transmitted data of the victim.\

Protection against MITM attacks

Reliable protection against MITM attacks is possible when the user takes several preventive actions and uses a combination of encryption and authentication methods by web application developers.

User actions:

• Avoid connecting to Wi-Fi hotspots that do not have password protection. Disable feature automatic connection to known access points - an attacker can disguise his Wi-Fi as legal.
• Pay attention to the browser notification about the transition to an insecure site. Such a message may indicate that you have been taken to a fake site of an attacker or that there are problems with the protection of a legitimate site.
• End the session with the application (logout) if it is not in use.
• Do not use public networks (cafe, park, hotel, etc.) for confidential transactions ( business correspondence, financial transactions, purchases in online stores, etc.).
• Use an up-to-date antivirus on your computer or laptop, it will help protect against attacks using malicious software.

Developers of web applications and websites should use the secure protocols TLS and HTTPS, which greatly complicate spoofing attacks by encrypting the transmitted data. Also, their use prevents interception of traffic in order to obtain authorization parameters and access keys.

It is considered good practice to protect TLS and HTTPS not only for authorization pages, but also for all other sections of the site. This reduces the chance of an attacker stealing a user's cookies while navigating through insecure pages after logging in.

Protection against MITM attacks is the responsibility of the user and telecom operator. For the user, the most important thing is not to lose vigilance, use only proven methods of accessing the Internet, and choose sites with HTTPS encryption to transfer personal data. Telecom operators can be recommended to use Deep Packet Inspection (DPI) systems to detect anomalies in data networks and prevent spoofing attacks.

Government agencies plan to use the MITM attack to protect citizens, and not to cause damage, unlike attackers. The interception of personal messages and other user traffic is carried out within the framework of the current legislation, is carried out by the decision of the judicial authorities to combat terrorism, drug trafficking and other prohibited activities. For ordinary users, "legitimate" MITM attacks are not dangerous.

You can almost always achieve the desired result in several ways. This also applies to the field of information security. Sometimes, to achieve the goal, you can brute, independently look for holes and develop sploits, or listen to what is transmitted over the network. And last option is often optimal. That is why today we will talk about tools that will help to catch valuable information for us from network traffic, using MITM attacks for this.

MITMf

Let's start with one of the more interesting candidates. This is a whole framework for man-in-the-middle attacks, built on top of sergio-proxy. Recently included in Kali Linux. To install it yourself, just clone the repository and run a couple of commands:

# setup.sh # pip install -r requirements.txt

# pip install -r requirements.txt

It has an architecture that can be extended by plug-ins. Among the main ones are the following:

• Spoof - allows you to redirect traffic using ARP / DHCP spoofing, ICMP redirects and modify DNS queries;
• Sniffer - this plugin monitors login attempts for various protocols;
• BeEFAutorun - allows you to automatically run BeEF modules based on the type of OS and client browser;
• AppCachePoison - performs a cache poisoning attack;
• SessionHijacking - hijacks sessions and saves received cookies in the firelis profile;
• BrowserProfiler - tries to get a list of plugins used by the browser;
• FilePwn - allows you to replace files sent over HTTP using Backdoor Factory and BDFProxy;
• Inject - injects arbitrary content into an HTML page;
• jskeylogger - Injects a JavaScript keylogger into client pages.

If this functionality is not enough for you, then you can always add your own by implementing the appropriate extension.

putty rider

Another noteworthy utility. True, unlike all the other tools considered today, it is very narrowly specialized. As the author of the project himself says, he was inspired to create such a utility by the fact that during penetration tests the most important data was located on Linux / UNIX servers, to which admins connected via SSH / Telnet / rlogin. And in most cases, accessing the administrators' machine was much easier than accessing the target server. Having penetrated the system administrator's machine, all that remains is to make sure that PuTTY is running and use this tool to build a reverse bridge to the attacker.

The utility allows not only to sniff "communication" between the administrator and remote server(including passwords), but also execute arbitrary shell commands within a given session. And all this will happen absolutely transparently for the user (administrator). If you are interested in technical details, for example, how the implementation of the PuTTY process is implemented, I recommend that you read the author's presentation.

A rather old utility that was born more than eight years ago. Designed to clone sessions by stealing cookies. For session hijacking, it has basic skills to detect hosts (in case of connecting to an open wireless network or habu) and conduct ARP poisoning. The only problem is that today, unlike eight years ago, almost all large companies like Yahoo or Facebook use SSL encryption, which makes this tool completely useless. Despite this, there are still enough resources on the Web that do not use SSL, so it's too early to write off the utility. Its advantages include the fact that it automatically integrates into Firefox and creates a separate profile for each intercepted session. Source is available in the repository, and you can build it yourself using the following sequence of commands:

# apt-get install build-essential libwxgtk2.8-dev libgtk2.0-dev libpcap-dev # g++ $(wx-config --cppflags --libs) -lpcap -o sessionthief *.cpp # setcap cap_net_raw,cap_net_admin=eip sessionthief

# apt-get install build-essential libwxgtk2.8-dev libgtk2.0-dev libpcap-dev # g++ $(wx-config --cppflags --libs) -lpcap -o sessionthief *.cpp # setcap cap_net_raw,cap_net_admin=eip sessionthief

Proxy Fuzz

ProzyFuzz has nothing to do directly with MITM attacks. As you can guess from the name, the tool is designed for fuzzing. This is a small non-deterministic network fuzzer implemented in python that randomly changes the contents of network traffic packets. Supports TCP and UDP protocols. Can be configured to fuzz only one side. Useful when you need to quickly test some network application (or protocol) and develop a PoC. Usage example:

Python proxyfuzz -l -r -p

python proxyfuzz -l -r -p

The list of options includes:

• w - sets the number of requests sent before fuzzing starts;
• c - fuzz only the client (otherwise both sides);
• s - fuzz only the server (otherwise both sides);
• u - UDP protocol (otherwise TCP is used).

The Middler

Presented at the DEF CON conference, a utility for carrying out MITM attacks on various protocols. The alpha version supported the HTTP protocol and had three cool plugins in its arsenal:

• plugin-beef.py - injects the Browser Exploitation Framework (BeEF) into any HTTP request coming from the local network;
• plugin-metasploit.py - injects into unencrypted (HTTP) requests an IFRAME that loads browser exploits from Metasploit;
• plugin-keylogger.py - Injects a JavaScript onKeyPress event handler for all text fields that will be sent over HTTPS, causing the browser to send the user's password character-by-character to the attacker's server before the entire form is submitted.

The Middler not only automatically analyzes network traffic and finds cookies in it, but also independently requests them from the client, that is, the process is automated to the maximum. The program guarantees the collection of all unprotected accounts in computer network(or public hotspot) to whose traffic it has access. For the program to work correctly, the following packages must be installed on the system: Scapy, libpcap, readline, libdnet, python-netfilter. Unfortunately, the repository has not been updated for a long time, so you will have to add new functionality yourself.

A console utility that allows you to interactively examine and modify HTTP traffic. Thanks to such skills, the utility is used not only by penetration testers / hackers, but also by ordinary developers who use it, for example, to debug web applications. It can be used to get detailed information about what requests the application makes and what responses it receives. Also, mitmproxy can help you learn how some REST APIs work, especially poorly documented ones.

Installation is extremely simple:

$ sudo aptitude install mitmproxy

It is worth noting that mitmproxy also allows you to intercept HTTPS traffic by issuing a self-signed certificate to the client. A good example of how to set up traffic interception and modification can be found.

Dsniff

Well, this utility is generally one of the first things that should come to mind as soon as you hear
"MITM attack". The tool is quite old, but continues to be actively updated, which is good news. It makes no sense to talk in detail about its capabilities; over the fourteen years of its existence, it has been covered on the network more than once. For example, in a guide like this:

or instructions from our website:

Lastly..

As usual, we have not considered all the utilities, but only the most popular ones, there are still many little-known projects that we might talk about someday. As you can see, there is no shortage of tools for carrying out MITM attacks, and, which happens not so often, one of the cool tools is implemented under Windows. There is nothing to say about nix systems - a whole variety. So I guess you can always find the right hijacking tool.
someone else's credentials. Oops, that is, for testing purposes.

Attack "man in the middle" (Eng. Man in the middle, MitM-attack) - a term in cryptography, denoting a situation where an attacker is able to read and modify messages exchanged by correspondents at will, and none of the latter can guess about his presence in the channel.

A method of compromising a communication channel, in which an attacker, having connected to a channel between counterparties, actively intervenes in the transmission protocol, deleting, distorting information or imposing false information.

Attack principle:

Let's say object "A" plans to send some information to object "B". Object "C" has knowledge about the structure and properties of the data transfer method used, as well as the fact of the planned transmission of the actual information that "C" plans to intercept.

To perform an attack, "C" is "represented" to object "A" as "B", and to object "B" as "A". Object "A", mistakenly believing that it is sending information to "B", sends it to object "C".

Object "C", having received the information, and having performed some actions with it (for example, copying or modifying for its own purposes) sends the data to the recipient itself - "B"; object "B", in turn, believes that the information was received by him directly from "A".

An example of a MitM attack:

Suppose Alice is in financial trouble and using an instant messaging program decides to ask John for a sum of money by sending a message:

Alice: John, hi!
Alice: Please send the encryption key, there is a small request!
John: Hello! Wait a second!

But, at this time, Mr. X, who, while analyzing traffic with a sniffer, noticed this message, and the words "encryption key", aroused curiosity. That's why he decided to intercept the following messages and replace them with the data he needed, and when he received the following message:

John: Here is my key: 1111_D

He changed John's key to his own, and sent a message to Alice:

John: Here is my key: 6666_M

Alice, unaware and thinking it is John's key, using the private key 6666_M, sends encrypted messages to John:

Alice: John, I'm in trouble and I need money urgently, please transfer $300 to my account: Z12345. Thank you. p.s. My key: 2222_A

Having received the message, Mister-X decrypts it using his key, reads it, and rejoicing, changes Alice's account number and encryption key to his own, encrypts the message with the key 1111_D, and sends John a message:

Alice: John, I have problems and I urgently need money, please transfer $300 to my account: Z67890. Thank you. p.s. My key: 6666_A

After receiving the message, John decrypts it using the key. 1111_D, and without even a doubt, will transfer money to the account Z67890...

And so Mr. X made $300 using the man-in-the-middle attack, but Alice now has to explain that she didn't get the money... And John? John has to prove to Alice that he sent them...

Implementation:

A similar type of attack is used in some software products for listening to the network, for example:

NetStumbler- a program with which you can collect a lot of useful data about a wireless network and solve some problems associated with its operation. NetStumbler allows you to determine the range of the network and help you accurately direct the antenna for communication over long distances. For each found access point, you can find out the MAC address, signal-to-noise ratio, the name of the service and the degree of its security. If the traffic is not encrypted, then the ability of the program to detect unauthorized connections will be useful.

dsniff- is a set of programs for network audit and penetration checks, provides passive network monitoring to search for data of interest (passwords, e-mail addresses, files, etc.), interception of network traffic that is normally inaccessible for analysis (for example, on a switched network), as well as the possibility of organizing MITM attacks to intercept SSH and HTTPS sessions by exploiting the shortcomings of PKI.

Cain & Abel- a free program that allows you to recover lost passwords for operating systems Windows family. Several recovery modes are supported: brute-force brute-force cracking, dictionary selection, viewing passwords hidden by asterisks, etc. There are also options for password detection by intercepting information packets and their subsequent analysis, recording network conversations, cache analysis, and others.

Ettercap- is a sniffer, packet interceptor and registrar for local Ethernet networks, which supports active and passive analysis of many protocols, as well as "tossing" own data into an existing connection and filtering "on the fly" without disturbing the synchronization of the connection. The program allows you to intercept SSH1, HTTPS and other secure protocols and provides the ability to decrypt passwords for the following protocols: TELNET, ftp, POP, RLOGIN, SSH1, icq, SMB, Mysql, HTTP, NNTP, X11, NAPSTER, IRC, RIP, BGP, SOCKS 5, IMAP 4, VNC, LDAP, NFS, SNMP, HALF LIFE, QUAKE 3, MSN, YMSG.

KARMA- a set of utilities for assessing the security of wireless clients, is a wireless sniffer that, by passively listening to 802.11 Probe Request frames, allows you to discover clients and their preferred / trusted networks. A fake access point can then be created for one of the requested networks, to which it can be automatically connected. High-level fake services can be used to steal personal data or exploit client-side vulnerabilities on the host.

airjack- a set of programs that, according to experts from the field of WiFi hacking, is best tool to generate various 802.11 frames. AirJack includes a number of utilities designed to detect a hidden ESSID, send session termination frames with a fake MAC, perform MitM attacks and modify it.

Opposition:

To avoid attacks of this type, it is enough for subscribers "A" and "B" to transfer digital signatures of public encryption keys to each other using a reliable channel. Then, when comparing key signatures in encryption sessions, it will be possible to establish with which key the data was encrypted, and whether the keys have been spoofed.