CVE-2021-3493

CRITICALNVD 8.89.0▲
EchelonGraph scoreHIGH confidence

Score elevated to 9.0 because this CVE is listed on the CISA Known Exploited Vulnerabilities catalog (added 2022-10-20), indicating real-world exploitation has been confirmed by US federal agencies. NVD baseline CVSS 8.8 retained for reference. Confidence: HIGH.

Triggered by: CISA KEV (actively exploited)
Sources: cisa_kev, epss, ghsa, nvd
Trending — 5 sources updated this weekExploited in the wild
9.0EG
EchelonGraph verdictPatch nowTreat as an emergency — this is being exploited.
  • Actively exploited in the wild (CISA-KEV)
CISA-KEV: ExploitedEPSS PROB: 49%CVSS: 8.8Exploit: cisa kev · ssvc active · Metasploit · epss top5pct · public exploitExposed: 0

A fix is available — apply it.

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 v3
8.8
EG Score
9.0(high)
EG Risk
81(Attend)
EG Risk 81/100SSVC: Attend

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity90% × 45%
Exploitation100% × 40%
Automatability0% × 15%
Action: Remediate soon — notable exploitation risk.
EPSS PROB
49%
EPSS %ILE
99%
KEV
⚠ Exploited

Published

April 17, 2021

Last Modified

October 28, 2025

Advisory Details (6)

Auto-updated Jun 2, 2026
Patch available. Sources: ubuntu.
generic

vfs: move cap_convert_nscap() call into vfs_setxattr() - kernel/git/torvalds/linux.git - Linux kernel source tree

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7c03e2cda4a584cadc398e8f6641ca9988a39d52
generic

Packet Storm

http://packetstormsecurity.com/files/165151/Ubuntu-Overlayfs-Local-Privilege-Escalation.html
generic

Packet Storm

http://packetstormsecurity.com/files/162866/Ubuntu-OverlayFS-Local-Privilege-Escalation.html
generic

Packet Storm

http://packetstormsecurity.com/files/162434/Kernel-Live-Patch-Security-Notice-LSN-0076-1.html
generic

oss-security - [CVE-2021-3493] Ubuntu Linux kernel overlayfs fs caps privilege escalation

https://www.openwall.com/lists/oss-security/2021/04/16/1
ubuntu Patch Available

USN-4917-1: Linux kernel vulnerabilities | Ubuntu security notices | Ubuntu

https://ubuntu.com/security/notices/USN-4917-1

Patch Availability(4)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntulinux-image-oem-20.04 (5.6.0.1054.50) @ focal2026-09-19ubuntu
ubuntulinux-image-virtual-hwe-20.04-edge (5.8.0.50.55) @ groovy2026-09-19ubuntu
ubuntugkeop (5.4.0-1009) @ focal2026-09-19ubuntu
ubuntulinux-image-virtual-lts-xenial (4.4.0.209.215) @ xenial2026-09-19ubuntu

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(4 across 4 ecosystems)
Debian:11(1)
PackageVulnerable rangeFixed inDependents
linux—5.10.38-1—
Debian:12(1)
PackageVulnerable rangeFixed inDependents
linux—5.10.38-1—
Debian:13(1)
PackageVulnerable rangeFixed inDependents
linux—5.10.38-1—
Debian:14(1)
PackageVulnerable rangeFixed inDependents
linux—5.10.38-1—

Weakness Classification(3)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

All Vendor Advisories

(4)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Data Freshness Timeline

(refreshed 96× in last 7d / 378× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 1,350 total refreshes for this CVE.

  1. 2026-09-19 03:53 UTCVendor advisory
  2. 2026-09-19 03:53 UTCGHSA enrichment
  3. 2026-09-18 23:55 UTCVendor advisory
  4. 2026-09-18 23:54 UTCGHSA enrichment
  5. 2026-09-18 19:56 UTCEG score recompute
  6. 2026-09-18 19:56 UTCVendor advisory
  7. 2026-09-18 19:56 UTCGHSA enrichment
  8. 2026-09-18 19:23 UTCEPSS rescore
  9. 2026-09-18 19:20 UTCCISA KEV update
  10. 2026-09-18 15:56 UTCGHSA enrichment
  11. 2026-09-18 14:15 UTCCISA KEV update
  12. 2026-09-18 11:53 UTCVendor advisory
  13. 2026-09-18 11:53 UTCGHSA enrichment
  14. 2026-09-18 07:54 UTCVendor advisory
  15. 2026-09-18 07:54 UTCGHSA enrichment
  16. 2026-09-18 03:55 UTCVendor advisory
  17. 2026-09-18 03:55 UTCGHSA enrichment
  18. 2026-09-17 23:56 UTCVendor advisory
  19. 2026-09-17 23:56 UTCGHSA enrichment
  20. 2026-09-17 19:57 UTCEG score recompute
  21. 2026-09-17 19:57 UTCVendor advisory
  22. 2026-09-17 19:57 UTCGHSA enrichment
  23. 2026-09-17 19:23 UTCEPSS rescore
  24. 2026-09-17 19:23 UTCEPSS rescore
  25. 2026-09-17 15:58 UTCVendor advisory
Show 75 more
  1. 2026-09-17 15:58 UTCGHSA enrichment
  2. 2026-09-17 11:59 UTCVendor advisory
  3. 2026-09-17 11:59 UTCGHSA enrichment
  4. 2026-09-17 08:00 UTCVendor advisory
  5. 2026-09-17 08:00 UTCGHSA enrichment
  6. 2026-09-17 04:01 UTCVendor advisory
  7. 2026-09-17 04:01 UTCGHSA enrichment
  8. 2026-09-17 00:02 UTCVendor advisory
  9. 2026-09-17 00:02 UTCGHSA enrichment
  10. 2026-09-16 20:03 UTCVendor advisory
  11. 2026-09-16 20:03 UTCGHSA enrichment
  12. 2026-09-16 16:05 UTCEG score recompute
  13. 2026-09-16 16:05 UTCVendor advisory
  14. 2026-09-16 16:04 UTCGHSA enrichment
  15. 2026-09-16 14:10 UTCCISA KEV update
  16. 2026-09-16 14:05 UTCEPSS rescore
  17. 2026-09-16 12:05 UTCVendor advisory
  18. 2026-09-16 12:05 UTCGHSA enrichment
  19. 2026-09-16 08:06 UTCEG score recompute
  20. 2026-09-16 08:05 UTCGHSA enrichment
  21. 2026-09-16 04:05 UTCGHSA enrichment
  22. 2026-09-16 00:05 UTCVendor advisory
  23. 2026-09-16 00:05 UTCGHSA enrichment
  24. 2026-09-15 20:05 UTCVendor advisory
  25. 2026-09-15 20:05 UTCGHSA enrichment
  26. 2026-09-15 16:05 UTCVendor advisory
  27. 2026-09-15 16:05 UTCGHSA enrichment
  28. 2026-09-15 12:06 UTCVendor advisory
  29. 2026-09-15 12:05 UTCGHSA enrichment
  30. 2026-09-15 08:06 UTCVendor advisory
  31. 2026-09-15 08:06 UTCGHSA enrichment
  32. 2026-09-15 04:07 UTCEG score recompute
  33. 2026-09-15 04:07 UTCVendor advisory
  34. 2026-09-15 04:07 UTCGHSA enrichment
  35. 2026-09-15 03:06 UTCEPSS rescore
  36. 2026-09-15 00:08 UTCVendor advisory
  37. 2026-09-15 00:08 UTCGHSA enrichment
  38. 2026-09-14 20:09 UTCVendor advisory
  39. 2026-09-14 20:09 UTCGHSA enrichment
  40. 2026-09-14 19:24 UTCCISA KEV update
  41. 2026-09-14 16:10 UTCVendor advisory
  42. 2026-09-14 16:10 UTCGHSA enrichment
  43. 2026-09-14 12:11 UTCVendor advisory
  44. 2026-09-14 12:11 UTCGHSA enrichment
  45. 2026-09-14 08:12 UTCVendor advisory
  46. 2026-09-14 08:12 UTCGHSA enrichment
  47. 2026-09-14 04:13 UTCVendor advisory
  48. 2026-09-14 04:13 UTCGHSA enrichment
  49. 2026-09-14 00:14 UTCVendor advisory
  50. 2026-09-14 00:14 UTCGHSA enrichment
  51. 2026-09-13 20:15 UTCVendor advisory
  52. 2026-09-13 20:15 UTCGHSA enrichment
  53. 2026-09-13 16:16 UTCVendor advisory
  54. 2026-09-13 16:16 UTCGHSA enrichment
  55. 2026-09-13 12:17 UTCVendor advisory
  56. 2026-09-13 12:17 UTCGHSA enrichment
  57. 2026-09-13 08:18 UTCVendor advisory
  58. 2026-09-13 08:17 UTCGHSA enrichment
  59. 2026-09-13 04:19 UTCVendor advisory
  60. 2026-09-13 04:19 UTCGHSA enrichment
  61. 2026-09-13 00:20 UTCVendor advisory
  62. 2026-09-13 00:20 UTCGHSA enrichment
  63. 2026-09-12 20:21 UTCVendor advisory
  64. 2026-09-12 20:21 UTCGHSA enrichment
  65. 2026-09-12 16:22 UTCEG score recompute
  66. 2026-09-12 16:22 UTCVendor advisory
  67. 2026-09-12 16:22 UTCGHSA enrichment
  68. 2026-09-12 14:57 UTCEPSS rescore
  69. 2026-09-12 12:23 UTCVendor advisory
  70. 2026-09-12 12:23 UTCGHSA enrichment
  71. 2026-09-12 08:23 UTCGHSA enrichment
  72. 2026-09-12 04:25 UTCVendor advisory
  73. 2026-09-12 04:25 UTCGHSA enrichment
  74. 2026-09-12 00:26 UTCVendor advisory
  75. 2026-09-12 00:26 UTCGHSA enrichment

Publicly available exploits

(6 references)

Working exploit code is in the public domain (1 Metasploit module) (5 GitHub PoCs). Defenders should treat patch urgency accordingly — public PoCs typically lead to mass-exploitation within 24-72 hours.

  • GitHub PoCAyham-Megdadi/Zero-Day-Legacy
    First seen Jul 5, 2026

    A vulnerable Boot-to-Root CTF lab machine simulating a hospital environment. Features a realistic 17-step attack chain including SQL Injection, XSS, Session Hijacking, SSH access, password cracking, privilege escalation via CVE-2021-3493, and full root compromise. Developed as a graduation project at Ajloun National University (ANU), awarded 97%.

    Open source ↗
  • GitHub PoCpuckiestyle/CVE-2021-3493
    First seen Oct 2, 2021
    Open source ↗
  • GitHub PoCinspiringz/CVE-2021-3493
    First seen Jul 7, 2021

    CVE-2021-3493 Ubuntu OverlayFS Local Privesc (Interactive Bash Shell & Execute Command Entered)

    Open source ↗
  • GitHub PoConeoy/CVE-2021-3493
    First seen Apr 22, 2021
    Open source ↗
  • GitHub PoCbriskets/CVE-2021-3493
    First seen Apr 19, 2021

    Ubuntu OverlayFS Local Privesc

    Open source ↗
  • Metasploitexploit/linux/local/cve_2021_3493_overlayfs✓ verified
    First seen Apr 12, 2021

    2021 Ubuntu Overlayfs LPE

    Open source ↗

Related CVEs(same vendor + same CWE)

Frequently asked(6)

What is CVE-2021-3493?
CVE-2021-3493 is a critical vulnerability published on April 17, 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…
When was CVE-2021-3493 disclosed?
CVE-2021-3493 was first published in the National Vulnerability Database on April 17, 2021, with the most recent update on October 28, 2025. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-3493 actively exploited?
Yes. CISA added CVE-2021-3493 to the Known Exploited Vulnerabilities catalog on October 20, 2022, affecting Linux Kernel. KEV listing indicates confirmed exploitation in the wild; this CVE warrants immediate patching attention.
What is the CVSS score of CVE-2021-3493?
CVE-2021-3493 has a CVSS v3 base score of 8.8 (NVD). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 9.0.
Which products are affected by CVE-2021-3493?
CVE-2021-3493 affects Linux Kernel. The full affected-products list, including version ranges and fixed versions, is shown in the Affected Packages section of this page.
How do I remediate CVE-2021-3493?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-3493, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

See which npm, PyPI, Go, and Maven packages are affected by CVE-2021-3493

Explore →

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