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Ubuntu Security Notice USN-6560-1
December 19, 2023
openssh vulnerabilities
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A security issue affects these releases of Ubuntu and its derivatives:
- Ubuntu 23.10
- Ubuntu 23.04
- Ubuntu 22.04 LTS
- Ubuntu 20.04 LTS
Summary:
Several security issues were fixed in OpenSSH.
Software Description:
- 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)
Update instructions:
The problem can be corrected by updating your system to the following
package versions:
Ubuntu 23.10:
   openssh-client                  1:9.3p1-1ubuntu3.1
   openssh-server                  1:9.3p1-1ubuntu3.1
Ubuntu 23.04:
   openssh-client                  1:9.0p1-1ubuntu8.6
   openssh-server                  1:9.0p1-1ubuntu8.6
Ubuntu 22.04 LTS:
   openssh-client                  1:8.9p1-3ubuntu0.5
   openssh-server                  1:8.9p1-3ubuntu0.5
Ubuntu 20.04 LTS:
   openssh-client                  1:8.2p1-4ubuntu0.10
   openssh-server                  1:8.2p1-4ubuntu0.10
In general, a standard system update will make all the necessary changes.
References:
   https://ubuntu.com/security/notices/USN-6560-1
   CVE-2023-28531, CVE-2023-48795
Package Information:
   https://launchpad.net/ubuntu/+source/openssh/1:9.3p1-1ubuntu3.1
   https://launchpad.net/ubuntu/+source/openssh/1:9.0p1-1ubuntu8.6
   https://launchpad.net/ubuntu/+source/openssh/1:8.9p1-3ubuntu0.5
   https://launchpad.net/ubuntu/+source/openssh/1:8.2p1-4ubuntu0.10