1. Ubuntu Security Notices
  2. USN-6560-1

USN-6560-1: OpenSSH vulnerabilities

Publication date

19 December 2023

Overview

Several security issues were fixed in OpenSSH.

Releases

Packages

  • openssh - secure shell (SSH) for secure access to remote machines

Details

Fabian Bäumer, Marcus Brinkmann, Jörg 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. (CVE-2023-48795)

Luci Stanescu discovered that OpenSSH incorrectly added destination
constraints when smartcard keys were added to ssh-agent, contrary to
expectations. This issue only affected Ubuntu 22.04 LTS, and Ubuntu 23.04.
(CVE-2023-28531)

Fabian Bäumer, Marcus Brinkmann, Jörg 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. (CVE-2023-48795)

Luci Stanescu discovered that OpenSSH incorrectly added destination
constraints when smartcard keys were added to ssh-agent, contrary to
expectations. This issue only affected Ubuntu 22.04 LTS, and Ubuntu 23.04.
(CVE-2023-28531)

Update instructions

In general, a standard system update will make all the necessary changes.

Learn more about how to get the fixes.

The problem can be corrected by updating your system to the following package versions:

Ubuntu Release Package Version
23.10 mantic openssh-client –  1:9.3p1-1ubuntu3.1
openssh-server –  1:9.3p1-1ubuntu3.1
23.04 lunar openssh-client –  1:9.0p1-1ubuntu8.6
openssh-server –  1:9.0p1-1ubuntu8.6
22.04 jammy openssh-client –  1:8.9p1-3ubuntu0.5
openssh-server –  1:8.9p1-3ubuntu0.5
20.04 focal openssh-client –  1:8.2p1-4ubuntu0.10
openssh-server –  1:8.2p1-4ubuntu0.10

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References

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