CVE-2021-3493

What the flaw is

The overlayfs stacking file system in Linux kernel does not properly validate the application of file capabilities against user namespaces, which could lead to privilege escalation.

Description as published by CISA. We have not independently reproduced it.

What CISA requires

Apply updates per vendor instructions.

This deadline is binding on US federal civilian agencies under BOD 22-01. It is not a legal deadline for anyone else, but it is a useful urgency signal — CISA sets it by how actively the flaw is being used, not by CVSS.

Public exploit code

206 public repositories referencing this CVE have been catalogued on GitHub. That volume usually means a reliable, widely-reproduced exploit. Treat this as a strong signal to prioritise patching, not as a verified working exploit — many such repositories are scanners, write-ups or forks rather than functional code.

• 0day404/vulnerability-poc
• 0xMarcio/cve
• 0xMat10/eJPT_Prep
• 0xWhoami35/root-kernel
• 0xabdoulaye/CTFs-Journey
• 0xfke/500-free-TryHackMe-rooms
• 0xkarthi/Tryhackme-Roadmap
• 0xneobyte/TryHackMe-Learning-Path-From-Beginner-to-Expert

Showing 8 of 206. Full list in the trickest/cve dataset.

Vendor advisories

• git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7c03e2cd
• nvd.nist.gov/vuln/detail/CVE-2021-3493

Primary sources

• NVD entry — CVSS score, CPE list and references
• CISA KEV catalog — the source for this page
• CVE Record at cve.org