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Security Advisory

USN-4916-1: Linux kernel vulnerabilities




Canonical Ubuntu

Versions Affected

  • Canonical Ubuntu 14.04
  • Canonical Ubuntu 16.04


It was discovered that the overlayfs implementation in the Linux kernel did not properly validate the application of file system capabilities with respect to user namespaces. A local attacker could use this to gain elevated privileges. (CVE-2021-3493)

Piotr Krysiuk discovered that the BPF JIT compiler for x86 in the Linux kernel did not properly validate computation of branch displacements in some situations. A local attacker could use this to cause a denial of service (system crash) or possibly execute arbitrary code. (CVE-2021-29154)

CVEs contained in this USN include: CVE-2021-29154, CVE-2021-3493.

Affected Cloud Foundry Products and Versions

Severity is high unless otherwise noted.

  • Xenial Stemcells
    • 456.x versions prior to 456.158
    • 621.x versions prior to 621.123
    • All other stemcells not listed.


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

  • 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


2021-04-29: Initial vulnerability report published.

Cloud Foundry Foundation Security Team Profile Image

Cloud Foundry Foundation Security Team, AUTHOR