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Security Advisory

USN-6561-1: libssh vulnerability

USN-6561-1: libssh vulnerability




Canonical Ubuntu

Versions Affected

  • Canonical Ubuntu 22.04


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. Update Instructions: Run `sudo pro fix USN-6561-1` to fix the vulnerability. The problem can be corrected by updating your system to the following package versions: libssh-gcrypt-dev – 0.9.3-2ubuntu2.4 libssh-4 – 0.9.3-2ubuntu2.4 libssh-gcrypt-4 – 0.9.3-2ubuntu2.4 libssh-dev – 0.9.3-2ubuntu2.4 libssh-doc – 0.9.3-2ubuntu2.4 No subscription required

CVEs contained in this USN include: CVE-2023-48795.

Affected Cloud Foundry Products and Versions

Severity is medium unless otherwise noted.

  • cflinuxfs4
    • All versions prior to 1.62.0
  • Jammy Stemcells
    • 1.x versions prior to 1.340
    • All other stemcells not listed.
  • CF Deployment
    • All versions with Jammy Stemcells prior to 1.340


Users of affected products are strongly encouraged to follow the mitigations below.

The Cloud Foundry project recommends upgrading the following releases:

  • cflinuxfs4
    • Upgrade all versions to 1.62.0 or greater
  • Jammy Stemcells
    • Upgrade 1.x versions to 1.340 or greater
    • All other stemcells should be upgraded to the latest version available on
  • CF Deployment
    • For all versions, upgrade Jammy Stemcells to 1.340 or greater


2024-04-04: Initial vulnerability report published.

Cloud Foundry Foundation Security Team Profile Image

Cloud Foundry Foundation Security Team, AUTHOR