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Ubuntu Security Notice USN-6561-1
Ubuntu Security Notice 6561-1 - Fabian Bäumer, Marcus Brinkmann, Joerg Schwenk discovered that the SSH protocol was vulnerable to a prefix truncation attack. If a remote attacker was able to intercept SSH communications, extension negotiation messages could be truncated, possibly leading to certain algorithms and features being downgraded. This issue is known as the Terrapin attack. This update adds protocol extensions to mitigate this issue.
==========================================================================Ubuntu Security Notice USN-6561-1December 19, 2023libssh vulnerability==========================================================================A security issue affects these releases of Ubuntu and its derivatives:- Ubuntu 23.10- Ubuntu 23.04- Ubuntu 22.04 LTS- Ubuntu 20.04 LTSSummary:A security issue was fixed in libssh.Software Description:- libssh: A tiny C SSH libraryDetails:Fabian Bäumer, Marcus Brinkmann, Jörg Schwenk discovered that the SSHprotocol was vulnerable to a prefix truncation attack. If a remote attackerwas able to intercept SSH communications, extension negotiation messagescould be truncated, possibly leading to certain algorithms and featuresbeing downgraded. This issue is known as the Terrapin attack. This updateadds protocol extensions to mitigate this issue.Update instructions:The problem can be corrected by updating your system to the followingpackage versions:Ubuntu 23.10: libssh-4 0.10.5-3ubuntu1.1Ubuntu 23.04: libssh-4 0.10.4-2ubuntu0.2Ubuntu 22.04 LTS: libssh-4 0.9.6-2ubuntu0.22.04.2Ubuntu 20.04 LTS: libssh-4 0.9.3-2ubuntu2.4In general, a standard system update will make all the necessary changes.References: https://ubuntu.com/security/notices/USN-6561-1 CVE-2023-48795Package Information: https://launchpad.net/ubuntu/+source/libssh/0.10.5-3ubuntu1.1 https://launchpad.net/ubuntu/+source/libssh/0.10.4-2ubuntu0.2 https://launchpad.net/ubuntu/+source/libssh/0.9.6-2ubuntu0.22.04.2 https://launchpad.net/ubuntu/+source/libssh/0.9.3-2ubuntu2.4
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### Summary Russh v0.40.1 and earlier is vulnerable to a novel prefix truncation attack (a.k.a. Terrapin attack), which allows a man-in-the-middle attacker to strip an arbitrary number of messages right after the initial key exchange, breaking SSH extension negotiation (RFC8308) in the process and thus downgrading connection security. ### Mitigations To mitigate this protocol vulnerability, OpenSSH suggested a so-called "strict kex" which alters the SSH handshake to ensure a Man-in-the-Middle attacker cannot introduce unauthenticated messages as well as convey sequence number manipulation across handshakes. Support for strict key exchange has been added to Russh in the patched version. **Warning: To take effect, both the client and server must support this countermeasure.** As a stop-gap measure, peers may also (temporarily) disable the affected algorithms and use unaffected alternatives like AES-GCM instead until patches are available. ### Details The SSH specifications of Ch...