CVE-2021-3493

Published: 15 April 2021

The overlayfs implementation in the linux kernel did not properly validate with respect to user namespaces the setting of file capabilities on files in an underlying file system. Due to the combination of unprivileged user namespaces along with a patch carried in the Ubuntu kernel to allow unprivileged overlay mounts, an attacker could use this to gain elevated privileges.

From the Ubuntu Security Team

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.

Notes

issue is specific to Ubuntu or any other distribution that
patched the kernel to allow unprivileged overlay mounts, prior to
the 5.11 commit (459c7c565ac36b) that permits it upstream.

Status

Severity score breakdown

References

• https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-3493
• https://ubuntu.com/security/notices/USN-4915-1
• https://ubuntu.com/security/notices/USN-4916-1
• https://ubuntu.com/security/notices/USN-4917-1
• https://www.openwall.com/lists/oss-security/2021/04/16/1
• NVD
• Launchpad
• Debian