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Security Advisory

USN-4906-1: Nettle vulnerability




Canonical Ubuntu

Versions Affected

  • Canonical Ubuntu 16.04
  • Canonical Ubuntu 18.04


It was discovered that Nettle incorrectly handled signature verification. A remote attacker could use this issue to cause Nettle to crash, resulting in a denial of service, or possibly force invalid signatures.

CVEs contained in this USN include: CVE-2021-20305.

Affected Cloud Foundry Products and Versions

Severity is medium unless otherwise noted.

  • cflinuxfs3
    • All versions prior to 0.235.0
  • Xenial Stemcells
    • 456.x versions prior to 456.158
    • 621.x versions prior to 621.123
    • All other stemcells not listed.
  • CF Deployment
    • All versions prior to 16.13.0


Users of affected products are strongly encouraged to follow the mitigations below. The Cloud Foundry project recommends upgrading the following releases:

  • cflinuxfs3
    • Upgrade all versions to 0.235.0 or greater
  • Xenial Stemcells
    • Upgrade 456.x versions to 456.158 or greater
    • Upgrade 621.x versions to 621.123 or greater
    • All other stemcells should be upgraded to the latest version available on
  • CF Deployment
    • Upgrade all versions to 16.13.0 or greater


2021-04-29: Initial vulnerability report published.

Cloud Foundry Foundation Security Team Profile Image

Cloud Foundry Foundation Security Team, AUTHOR