CVEs / CVE-2021-3493
CVE-2021-3493: Linux Kernel Privilege Escalation Vulnerability
- Known exploited in the CISA KEV catalog since 20 Oct 2022
- high 7.8 CVSS 3.1 (NVD)
- EPSS 49.1% chance of exploitation in the next 30 days, higher than 98% of CVEs (30 Oct 2026)
- Last changed at its sources
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Summary
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
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.
Affected and fixed versions
| Product | Affected | Fixed in |
|---|---|---|
| Ubuntu linux kernel | from 5.8 kernel, before 5.8.0-50.56 | 5.8.0-50.56 |
| Ubuntu linux kernel | from 5.4 kernel, before 5.4.0-72.80 | 5.4.0-72.80 |
| Ubuntu linux kernel | from 4.15 kernel, before 4.15.0-142.146 | 4.15.0-142.146 |
| Ubuntu linux kernel | from 4.4 kernel, before 4.4.0-209.241 | 4.4.0-209.241 |
Exploitation
| In CISA KEV since | 20 Oct 2022 |
|---|---|
| Due date for US federal agencies | 10 Nov 2022 |
| Used in ransomware campaigns | Unknown |
| Required action | Apply updates per vendor instructions. |
Severity
| CVSS 3.1 | 7.8 highCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:HScored by NVD |
|---|---|
| Weakness | CWE-270, CWE-863 |
References
- CVE-2021-3493 on NVD
- CVE-2021-3493 in the CISA KEV catalog
- https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7c03e2cda4a584cadc398e8f6641ca9988a39d52 (cited by CISA)
- CVE-2021-3493 on OSV
- http://packetstormsecurity.com/files/162434/Kernel-Live-Patch-Security-Notice-LSN-0076-1.html Exploit, Third Party Advisory, VDB Entry
- http://packetstormsecurity.com/files/162866/Ubuntu-OverlayFS-Local-Privilege-Escalation.html Press/Media Coverage, Third Party Advisory, VDB Entry
- http://packetstormsecurity.com/files/165151/Ubuntu-Overlayfs-Local-Privilege-Escalation.html Exploit, Third Party Advisory, VDB Entry
- https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7c03e2cda4a584cadc398e8f6641ca9988a39d52 Mailing List, Patch, Third Party Advisory
- https://ubuntu.com/security/notices/USN-4917-1 Vendor Advisory
- https://www.openwall.com/lists/oss-security/2021/04/16/1 Mailing List, Third Party Advisory
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-3493 US Government Resource
Sources
Exploitation status from the CISA Known Exploited Vulnerabilities catalog. EPSS scores from FIRST. Descriptions, severity and references from the National Vulnerability Database. Open-source package versions from OSV (CC-BY 4.0). Text is shown as each source states it; Stackurity does not edit it. Check the vendor's advisory before acting.
This product uses data from the NVD API but is not endorsed or certified by the NVD.