Stormshield Network Security

CVSS v3.1 Overall Score: 6.4      

Analysis

Impacted version

The Terrapin attack is a vulnerability in the SSH protocol itself. It results in the compromised client mistakenly perceiving that the server does not support recent signature algorithms used in user authentication. This vulnerability can be exploited through a man-in-the-middle (MitM) attack.

The vulnerability impacts all SSH connections and is specifically focused on the OpenSSH implementation. The vulnerable OpenSSH configurations are:

• chacha20-poly1305@openssh.com
• Any AES(128|192|256)-cbc ciphers
• Any MACs that use Encrypt-then-MAC (EtM), such as hmac-(sha2-512|sha2-256|sha1|sha1-96|md5-96|md5)-etm@openssh.com and umac-(128|64)-etm@openssh.com

Note that : AES(128|192|256)-cbc ciphers, hmac-(sha1|sha1-96|md5-96|md5)-etm@openssh.com and umac-64-etm@openssh.com MACs are usually deactivated by default.

The risk associated with this vulnerability is mitigated if the deployment recommendations for SNS, as describe in the installation guide, have been respected.

• All SNS versions

Workaround solution

Solution

It’s important to note that the default OpenSSH configurations is vulnerable to this attack because it allow the use of the ChaCha20-Poly1305 cipher. Mitigating this vulnerability involves disabling or removing these vulnerable configurations. Please follow these steps:

• Open an SSH connection to the firewall.
• Edit the file ConfigFiles/system.
  • In the [SSHCiphers] section, set the values to 0 for the following Ciphers:
    • chacha20-poly1305@openssh.com
    • CBC suites (aes128-cbc, aes192-cbc, and aes256-cbc).
  • In the [SSHMACs] section, set the values to 0 for the following MACs:
    • hmac-sha1-etm@openssh.com
    • hmac-sha2-256-etm@openssh.com
    • hmac-sha2-512-etm@openssh.com
    • umac-64-etm@openssh.com
    • umac-128-etm@openssh.com
    • hmac-sha1-96-etm@openssh.com
    • hmac-md5-etm@openssh.com
    • hmac-md5-96-etm@openssh.com
• Once you’ve made these adjustments, reboot the SNS.

The following versions will fix this vulnerability:

• SNS 4.7.4
• SNS 4.6.11
• SNS 4.3.24
• SNS 3.11.28
• SNS 3.7.40