CVE-2021-3493The 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.
Updated under an hour ago ()
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It affects Ubuntu linux kernel and 1 other product. Add what you run to find out whether that includes you.
CISA lists it as known exploited since Oct 20, 2022; federal agencies had to remediate by Nov 10, 2022. Treat that date as your deadline.
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Free account, 1 product
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.
- CVSS
- 8.8 HIGH (v3.1, CNA)CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
- Weakness (CWE)
- CWE-270
- Known exploited
- Added to CISA KEV Oct 20, 2022; federal remediation due Nov 10, 2022Apply updates per vendor instructions.
- EPSS (exploitation in the next 30 days)
- 49.17% (percentile 99)
- Assigned by
- canonical
- NVD analysis
- Analyzed
- Record last updated
- Oct 21, 2025
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
Ubuntu linux kernel ubuntu:linux_kernel (from the name) | from 5.8 kernel before 5.8.0-50.56; from 5.4 kernel before 5.4.0-72.80; from 4.15 kernel before 4.15.0-142.146; from 4.4 kernel before 4.4.0-209.241 | CNA record |
canonical ubuntu_linux canonical:ubuntu_linux | before 18.04; from 18.04.1 before 20.04; before 20.10 | NVD |
References
- https://ubuntu.com/security/notices/USN-4917-1x-refsource-misc, vendor-advisory
- https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7c03e2cda4a584cadc398e8f6641ca9988a39d52x-refsource-misc, mailing-list, patch, third-party-advisory
- https://www.openwall.com/lists/oss-security/2021/04/16/1x-refsource-misc, mailing-list, third-party-advisory
- http://packetstormsecurity.com/files/162434/Kernel-Live-Patch-Security-Notice-LSN-0076-1.htmlx-refsource-misc, exploit, third-party-advisory, vdb-entry
- http://packetstormsecurity.com/files/162866/Ubuntu-OverlayFS-Local-Privilege-Escalation.htmlx-refsource-misc, press/media-coverage, third-party-advisory, vdb-entry
- http://packetstormsecurity.com/files/165151/Ubuntu-Overlayfs-Local-Privilege-Escalation.htmlx-refsource-misc, exploit, third-party-advisory, vdb-entry
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-3493us-government-resource
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.