# CVE-2021-3493

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.

- Page: https://www.vulneraibility.com/cve/CVE-2021-3493
- CVSS: 8.8
- Known exploited: yes, in CISA KEV since 2022-10-20; CISA due date 2022-11-10
- EPSS: 49.17% (percentile 98.9)
- Public exploit code: 1 Metasploit module · 21 GitHub proofs of concept (first 2021-04-19)
- CISA SSVC: exploitation active, automatable no, technical impact total (assessed 2025-02-07)
- Weakness: CWE-270
- Published: 2021-04-17

## Affected versions

- Ubuntu linux kernel: affected >= 5.8 kernel and < 5.8.0-50.56; >= 5.4 kernel and < 5.4.0-72.80; >= 4.15 kernel and < 4.15.0-142.146; >= 4.4 kernel and < 4.4.0-209.241

A version outside these ranges is not a statement that it is unaffected.

## References

- [other] https://ubuntu.com/security/notices/USN-4917-1
- [other] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7c03e2cda4a584cadc398e8f6641ca9988a39d52
- [other] https://www.openwall.com/lists/oss-security/2021/04/16/1
- [other] http://packetstormsecurity.com/files/162434/Kernel-Live-Patch-Security-Notice-LSN-0076-1.html
- [other] http://packetstormsecurity.com/files/162866/Ubuntu-OverlayFS-Local-Privilege-Escalation.html
- [other] http://packetstormsecurity.com/files/165151/Ubuntu-Overlayfs-Local-Privilege-Escalation.html
- [other] https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-3493

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Summary, impact and action are written by the vulneraibility.com AI analysis pipeline from the CVE record, NVD, CISA and FIRST data; verify against the references.