Fabian Bäumer

The issue, also known as a Terrapin attack, allows an attacker who can intercept traffic between the client and server to drop certain packets, potentially downgrading or disabling some security features. This could cause the client and server to end up with a connection that has reduced security.

The SSH transport protocol with certain OpenSSH extensions is vulnerable to a prefix truncation attack, known as the Terrapin attack. This attack allows a man-in-the-middle attacker to strip an arbitrary number of messages right after the initial key exchange, breaking SSH extension negotiation and downgrading connection security. The attack works by injecting arbitrary SSH MSG IGNORE messages during the initial key exchange and removing the same number of messages just after the initial key exchange has concluded. This is possible due to missing authentication of the excess SSH MSG IGNORE messages and the fact that the implicit sequence numbers used within the SSH protocol are only checked after the initial key exchange.

The issue is related to OS command injection in OpenSSH, which might occur if a user name or host name has shell metacharacters and this name is referenced by an expansion token in certain situations. For example, an untrusted Git repository can have a submodule with shell metacharacters in a user name or host name. The estimated number of potentially affected devices worldwide is around 116,742,290, mainly distributed in the United States, China, and other countries.

The issue is related to errors in key management in the ssh-agent tool of OpenSSH. It allows an attacker to disclose protected information by exploiting certain destination constraints that are not fully applied when adding PKCS#11-hosted private keys. Specifically, when destination constraints are specified, they are only applied to the first key, even if a PKCS#11 token returns multiple keys. This can be exploited by sending a specially crafted request to obtain sensitive information, which can then be used to launch further attacks against the affected system.