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We found out that in contrast to public knowledge, the Pre-Shared Key (PSK) authentication method in main mode of IKEv1 is susceptible to offline dictionary attacks. This requires only a single active Man-in-the-Middle attack. Thus, if low entropy passwords are used as PSKs, this can easily be broken.

This week at the USENIX Security conference, Dennis Felsch will present our research paper on IPsec attacks: The Dangers of Key Reuse: Practical Attacks on IPsec IKE. [alternative link to the paper]

In his blog post, Dennis showed how to attack the public key encryption based authentication methods of IKEv1 (PKE & RPKE) and how to use this attack against IKEv2 signature based authentication method. In this blog post, I will focus on another interesting finding regarding IKEv1 and the Pre-Shared Key authentication.

IPsec and Internet Key Exchange (IKE)

IPsec enables cryptographic protection of IP packets. It is commonly used to build VPNs (Virtual Private Networks). For key establishment, the IKE protocol is used. IKE exists in two versions, each with different modes, different phases, several authentication methods, and conﬁguration options. Therefore, IKE is one of the most complex cryptographic protocols in use.

In version 1 of IKE (IKEv1), four authentication methods are available for Phase 1, in which initial authenticated keying material is established: Two public key encryption based methods, one signature based method, and a PSK (Pre-Shared Key) based method.

The relationship between IKEv1 Phase 1, Phase 2, and IPsec ESP. Multiple simultaneous Phase 2 connections can be established from a single Phase 1 connection. Grey parts are encrypted, either with IKE derived keys (light grey) or with IPsec keys (dark grey). The numbers at the curly brackets denote the number of messages to be exchanged in the protocol.

Pre-Shared Key authentication

As shown above, Pre-Shared Key authentication is one of three authentication methods in IKEv1. The authentication is based on the knowledge of a shared secret string. In reality, this is probably some sort of password.

The IKEv1 handshake for PSK authentication looks like the following (simplified version):

In the first two messages, the session identifier (inside HDR) and the cryptographic algorithms (proposals) are selected by initiator and responder.

In messages 3 and 4, they exchange ephemeral Diffie-Hellman shares and nonces. After that, they compute a key k by using their shared secret (PSK) in a PRF function (e.g. HMAC-SHA1) and the previously exchanged nonces. This key is used to derive additional keys (k_a, k_d, k_e). The key k_d is used to compute MAC_I over the session identifier and the shared diffie-hellman secret g^xy. Finally, the key k_e is used to encrypt ID_I (e.g. IPv4 address of the peer) and MAC_I.

Weaknesses of PSK authentication

It is well known that the aggressive mode of authentication in combination with PSK is insecure and vulnerable against off-line dictionary attacks, by simply eavesedropping the packets. For example, in strongSwan it is necessary to set the following configuration flag in order to use it:

charon.i_dont_care_about_security_and_use_aggressive_mode_psk=yes

For the main mode, we found a similar attack when doing some minor additional work. For that, the attacker needs to waits until a peer A (initiator) tries to connect to another peer B (responder). Then, the attacker acts as a man-in-the middle and behaves like the peer B would, but does not forward the packets to B.

From the picture above it should be clear that an attacker who acts as B can compute (g^xy) and receives the necessary public values session ID, n_I, n_R. However, the attacker does not know the PSK. In order to mount a dictionary attack against this value, he uses the nonces, and computes a candidate for k for every entry in the dictionary. It is necessary to make a key derivation for every k with the values of the session identifiers and shared Diffie-Hellmann secret the possible keys k_a, k_d and k_e. Then, the attacker uses k_e in order to decrypt the encrypted part of message 5. Due to ID_I often being an IP address plus some additional data of the initiator, the attacker can easily determine if the correct PSK has been found.

Who is affected?

This weakness exists in the IKEv1 standard (RFC 2409). Every software or hardware that is compliant to this standard is affected. Therefore, we encourage all vendors, companies, and developers to at least ensure that high-entropy Pre-Shared Keys are used in IKEv1 configurations.

In order to verify the attack, we tested the attack against strongSWAN 5.5.1.

Proof-of-Concept

We have implemented a PoC that runs a dictionary attack against a network capture (pcapng) of a IKEv1 main mode session. As input, it also requires the Diffie-Hellmann secret as described above. You can find the source code at github. We only tested the attack against strongSWAN 5.5.1. If you want to use the PoC against another implementation or session, you have to adjust the idHex value in main.py.

Responsible Disclosure

We reported our ﬁndings to the international CERT at July 6th, 2018. We were informed that they contacted over 250 parties about the weakness. The CVE ID for it is CVE-2018-5389 [cert entry].

Credits

On August 10th, 2018, we learned that this attack against IKEv1 main mode with PSKs was previously described by David McGrew in his blog post Great Cipher, But Where Did You Get That Key?. We would like to point out that neither we nor the USENIX reviewers nor the CERT were obviously aware of this.
On August 14th 2018, Graham Bartlett (Cisco) email us that he presented the weakness of PSK in IKEv2 in several public presentations and in his book.
On August 15th 2018, we were informed by Tamir Zegman that John Pliam described the attack on his web page in 1999.

FAQs

Do you have a name, logo, any merchandising for the attack?
No.
Have I been attacked?
We mentioned above that such an attack would require an active man-in-the-middle attack. In the logs this could look like a failed connection attempt or a session timed out. But this is a rather weak indication and no evidence for an attack.
What should I do?
If you do not have the option to switch to authentication with digital signatures, choose a Pre-Shared Key that resists dictionary attacks. If you want to achieve e.g. 128 bits of security, configure a PSK with at least 19 random ASCII characters. And do not use something that can be found in public databases.
Am I safe if I use PSKs with IKEv2?
No, interestingly the standard also mentions that IKEv2 does not prevent against off-line dictionary attacks.
Where can I learn more?
You can read the paper. [alternative link to the paper]
What else does the paper contain?
The paper contains a lot more details than this blogpost. It explains all authentication methods of IKEv1 and it gives message flow diagrams of the protocol. There, we describe a variant of the attack that uses the Bleichenbacher oracles to forge signatures to target IKEv2.

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Social engineering is a nontechnical method of breaking into a system or network. It's the process of deceiving users of a system and convincing them to perform acts useful to the hacker, such as giving out information that can be used to defeat or bypass security mechanisms. Social engineering is important to understand because hackers can use it to attack the human element of a system and circumvent technical security measures. This method can be used to gather information before or during an attack.

A social engineer commonly uses the telephone or Internet to trick people into revealing sensitive information or to get them to do something that is against the security policies of the organization. By this method, social engineers exploit the natural tendency of a person to trust their word, rather than exploiting computer security holes. It's generally agreed that users are the weak link in security; this principle is what makes social engineering possible.

The most dangerous part of social engineering is that companies with authentication processes, firewalls, virtual private networks, and network monitoring software are still wide open to attacks, because social engineering doesn't assault the security measures directly. Instead, a social-engineering attack bypasses the security measures and goes after the human element in an organization.

Types of Social Engineering-Attacks

There are two types of Social Engineering attacks

Human-Based

Human-based social engineering refers to person-to-person interaction to retrieve the desired information. An example is calling the help desk and trying to find out a password.

Computer-Based

Computer-based social engineering refers to having computer software that attempts to retrieve the desired information. An example is sending a user an email and asking them to reenter a password in a web page to confirm it. This social-engineering attack is also known as phishing.

Human-Based Social Engineering

Human-Based further categorized as follow:

Impersonating an Employee or Valid User

In this type of social-engineering attack, the hacker pretends to be an employee or valid user on the system. A hacker can gain physical access by pretending to be a janitor, employee, or contractor. Once inside the facility, the hacker gathers information from trashcans, desktops, or computer systems.

Posing as an Important User

In this type of attack, the hacker pretends to be an important user such as an executive or high-level manager who needs immediate assistance to gain access to a computer system or files. The hacker uses intimidation so that a lower-level employee such as a help desk worker will assist them in gaining access to the system. Most low-level employees won't question someone who appears to be in a position of authority.

Using a Third Person

Using the third-person approach, a hacker pretends to have permission from an authorized source to use a system. This attack is especially effective if the supposed authorized source is on vacation or can't be contacted for verification.

Calling Technical Support

Calling tech support for assistance is a classic social-engineering technique. Help desk and technical support personnel are trained to help users, which makes them good prey for social-engineering attacks.

Shoulder Surfing

Shoulder surfing is a technique of gathering passwords by watching over a person's shoulder while they log in to the system. A hacker can watch a valid user log in and then use that password to gain access to the system.

Dumpster Diving

Dumpster diving involves looking in the trash for information written on pieces of paper or computer printouts. The hacker can often find passwords, filenames, or other pieces of confidential information.

Computer-Based Social Engineering

Computer-based social-engineering attacks can include the following:

Email attachments
Fake websites
Pop-up windows

Insider Attacks

If a hacker can't find any other way to hack an organization, the next best option is to infiltrate the organization by getting hired as an employee or finding a disgruntled employee to assist in the attack. Insider attacks can be powerful because employees have physical access and are able to move freely about the organization. An example might be someone posing as a delivery person by wearing a uniform and gaining access to a delivery room or loading dock. Another possibility is someone posing as a member of the cleaning crew who has access to the inside of the building and is usually able to move about the offices. As a last resort, a hacker might bribe or otherwise coerce an employee to participate in the attack by providing information such as passwords.

Identity Theft

A hacker can pose as an employee or steal the employee's identity to perpetrate an attack. Information gathered in dumpster diving or shoulder surfing in combination with creating fake ID badges can gain the hacker entry into an organization. Creating a persona that can enter the building unchallenged is the goal of identity theft.

Phishing Attacks

Phishing involves sending an email, usually posing as a bank, credit card company, or other financial organization. The email requests that the recipient confirm banking information or reset passwords or PINs. The user clicks the link in the email and is redirected to a fake website. The hacker is then able to capture this information and use it for financial gain or to perpetrate other attacks. Emails that claim the senders have a great amount of money but need your help getting it out of the country are examples of phishing attacks. These attacks prey on the common person and are aimed at getting them to provide bank account access codes or other confidential information to the hacker.

Online Scams

Some websites that make free offers or other special deals can lure a victim to enter a username and password that may be the same as those they use to access their work system.
The hacker can use this valid username and password once the user enters the information in the website form. Mail attachments can be used to send malicious code to a victim's system, which could automatically execute something like a software keylogger to capture passwords. Viruses, Trojans, and worms can be included in cleverly crafted emails to entice a victim to open the attachment. Mail attachments are considered a computer-based social-engineering attack.Related links

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Welcome to my 2nd tutorial of the series of networking. In this video I've briefly described peer to peer network (P2P). Moreover, you'll see how to make a peer to peer network? How it's working? How we can intercept traffic over the network by using Wireshark? and many more. Wireshark tool is integrated with eNSP so it'll be installed automatically when you install the eNSP. On the other hand, you can install the Wireshark for your personal use from its website.

What is Peer to Peer (P2P) network?

As when devices are connected with each other for the sake of communication that'll be known as a Network. Now what is peer to peer network? In P2P network each and every device is behaving like a server and a client as well. Moreover They are directly connected with each other in such a way that they can send and received data to other devices at the same time and there is no need of any central server in between them.

There is a question that mostly comes up into our minds that Is it possible to capture data from the network? So the answer is yes. We can easily captured data from the network with the help of tools that have been created for network troubleshooting, so whenever there will be some issues happening to the network so we fixed that issues with the help of tools. Most usable tool for data capturing that every network analyst used named Wireshark but there are so many other tools available over the internet like SmartSniff, Ethereal, Colasoft Capsa Network Analyze, URL Helper, SoftX HTTP Debugger and many more.

What is Wireshark?

Wireshark is an open source network analyzer or sniffer used to capture packets from the network and tries to display the brief information about the packets. It is also used for software and communication protocol development. Moreover, Wireshark is the best tool to intercept the traffic over the network.

Figura 2: Bad Guys Never Sleep

Curiosamente, en esa charla hablaba de las estafa de los BitCoins usando la imagen de personas populares, que al cabo del tiempo han hecho con mi imagen. Así que ten mucho cuidado con tu dinero y no te creas todas las Fake News que veas por la red.

El segundo vídeo que so dejo es una entrevista que me hizo hace muy pocos días el periodista Juan Gómez para el programa de radio Nueva Dimensión donde hablamos de de hacking, de los riesgos de privacidad, la inteligencia artificial usada para suplantar personas, etcétera...

Figura 3: Entrevista a Chema Alonso en Nueva Dimensión

Mucho e lo que hablamos se basa en la conferencia que dicté como Keynote en el Security Innovation Day 2019 de ElevenPaths, que si no las visto la tienes aquí mismo. Mucho de lo que cuento en la entrevista lo puedes ver en directo con demos.

Figura 4: Keynote de Chema Alonso en Security Innovation Day 2019

Y por último, un nuevo Podcast de ElevenPaths Radio, en este caso con Josep Albors de ESET y Andrés Naranjo, aka TheXXLMan, hablando de Ciberseguridad & Gaming, que, estoy convencido, a los gamers os resultará más que interesante.

Figura 5: ElevenPaths Radio: Ciberseguridad & Gaming

Y nada más, si queréis contactar con alguno de nosotros, ya sabéis que gracias a ESET puedes conseguir 100 Tempos gratis en MyPublicInbox.

Saludos Malignos!

Autor: Chema Alonso (Contactar con Chema Alonso)