CVE-2021-33909

HIGHNVD 7.87.8—
EchelonGraph scoreMEDIUM confidence

Score 7.8 from GitHub Security Advisory (severity: HIGH) published 2022-05-24. NVD baseline CVSS 7.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
Elevated
7.8
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 10%CVSS: 7.8Exploit: NoneExposed: 0

A fix is available — apply it.

fs/seq_file.c in the Linux kernel 3.16 through 5.13.x before 5.13.4 does not properly restrict seq buffer allocations, leading to an integer overflow, an Out-of-bounds Write, and escalation to root by an unprivileged user, aka CID-8cae8cd89f05.

CVSS v3
7.8
EG Score
7.8(medium)
EPSS
95.0%
KEV
Not listed

Published

July 20, 2021

Last Modified

November 21, 2024

References (40)

Vendor Advisories for CVE-2021-33909(13)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Patch Availability(23)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntulinux-oem-20.04b (5.10.0.1038.40) @ focal2026-05-26ubuntu
ubuntulowlatency-4.4 (4.4.0-168) @ xenial2026-05-26ubuntu
ubuntulinux-virtual-hwe-20.04-edge (5.11.0.25.27) @ hirsute2026-05-26ubuntu
ubuntukernel-image-5.8.0-63-generic-lpae-di (5.8.0-63.71) @ groovy2026-05-26ubuntu
ubuntulinux-modules-5.4.0-1021-gkeop (5.4.0-1021.22) @ focal2026-05-26ubuntu
ubuntuvlan-modules-4.15.0-151-generic-di (4.15.0-151.157~16.04.1) @ xenial2026-05-26ubuntu
ubuntuoem (4.15.0-1063) @ bionic2026-05-26ubuntu
redhatredhat-virtualization-host-0:4.4.7-20210715.1.el8_42021-07-22redhat
redhatkpatch-patch2021-07-21redhat
redhatkernel-rt-0:3.10.0-1160.36.2.rt56.1179.el72021-07-21redhat
redhatkernel-0:3.10.0-1160.36.2.el72021-07-21redhat
redhatkernel-0:3.10.0-1062.52.2.el72021-07-21redhat
redhatredhat-virtualization-host-0:4.3.17-20210713.0.el7_92021-07-21redhat
redhatkernel-0:3.10.0-693.90.2.el72021-07-20redhat
redhatkernel-0:3.10.0-327.98.2.el72021-07-20redhat
redhatkernel-0:3.10.0-514.90.2.el72021-07-20redhat
redhatkernel-0:3.10.0-957.78.2.el72021-07-20redhat
redhatkernel-0:4.18.0-305.10.2.el8_42021-07-20redhat
redhatkernel-0:4.18.0-147.51.2.el8_12021-07-20redhat
redhatkernel-rt-0:4.18.0-193.60.2.rt13.112.el8_22021-07-20redhat
redhatkernel-0:4.18.0-193.60.2.el8_22021-07-20redhat
redhatkernel-0:2.6.32-754.41.2.el62021-07-20redhat
redhatkernel-rt-0:4.18.0-305.10.2.rt7.83.el8_42021-07-20redhat

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.

Weakness Classification(3)

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

Additional Vendor Advisories

(12)

Vendors that published advisories for this CVE beyond the curated set above. Broader coverage but minimal per-row detail — click through for the original advisory.

Data Freshness Timeline

(refreshed 8× in last 7d / 43× 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.

  1. 2026-07-12 05:44 UTCEPSS rescore
  2. 2026-07-12 05:44 UTCEPSS rescore
  3. 2026-07-11 08:25 UTCEPSS rescore
  4. 2026-07-11 08:25 UTCEPSS rescore
  5. 2026-07-09 19:07 UTCEPSS rescore
  6. 2026-07-08 15:12 UTCEPSS rescore
  7. 2026-07-07 13:43 UTCEPSS rescore
  8. 2026-07-06 16:25 UTCEPSS rescore
  9. 2026-07-06 02:21 UTCEPSS rescore
  10. 2026-07-05 02:28 UTCEPSS rescore
  11. 2026-07-05 02:28 UTCEPSS rescore
  12. 2026-07-04 06:29 UTCEPSS rescore
  13. 2026-07-04 06:29 UTCEPSS rescore
  14. 2026-07-01 15:04 UTCEPSS rescore
  15. 2026-06-30 23:20 UTCEPSS rescore
  16. 2026-06-30 23:20 UTCEPSS rescore
  17. 2026-06-30 23:00 UTCOSV refresh
  18. 2026-06-28 14:05 UTCEPSS rescore
  19. 2026-06-28 04:54 UTCEPSS rescore
  20. 2026-06-28 04:54 UTCEPSS rescore
  21. 2026-06-27 03:06 UTCEPSS rescore
  22. 2026-06-25 13:48 UTCEPSS rescore
  23. 2026-06-25 13:48 UTCEPSS rescore
  24. 2026-06-24 14:03 UTCEPSS rescore
  25. 2026-06-24 14:03 UTCEPSS rescore
Show 58 more
  1. 2026-06-23 21:31 UTCEPSS rescore
  2. 2026-06-23 21:31 UTCEPSS rescore
  3. 2026-06-22 14:24 UTCEPSS rescore
  4. 2026-06-22 14:24 UTCEPSS rescore
  5. 2026-06-21 14:55 UTCEPSS rescore
  6. 2026-06-21 01:58 UTCEPSS rescore
  7. 2026-06-21 01:58 UTCEPSS rescore
  8. 2026-06-19 19:24 UTCEPSS rescore
  9. 2026-06-19 19:24 UTCEPSS rescore
  10. 2026-06-18 17:51 UTCEPSS rescore
  11. 2026-06-18 17:51 UTCEPSS rescore
  12. 2026-06-17 17:51 UTCEPSS rescore
  13. 2026-06-16 17:51 UTCEPSS rescore
  14. 2026-06-16 17:51 UTCEPSS rescore
  15. 2026-06-15 17:46 UTCEPSS rescore
  16. 2026-06-14 23:15 UTCEPSS rescore
  17. 2026-06-13 22:58 UTCEPSS rescore
  18. 2026-06-13 22:58 UTCEPSS rescore
  19. 2026-06-13 01:46 UTCOSV refresh
  20. 2026-06-12 23:10 UTCEPSS rescore
  21. 2026-06-12 23:10 UTCEPSS rescore
  22. 2026-06-11 13:58 UTCEPSS rescore
  23. 2026-06-10 22:16 UTCEPSS rescore
  24. 2026-06-10 13:20 UTCEPSS rescore
  25. 2026-06-08 14:15 UTCEPSS rescore
  26. 2026-06-08 14:15 UTCEPSS rescore
  27. 2026-06-07 15:23 UTCEPSS rescore
  28. 2026-06-07 15:23 UTCEPSS rescore
  29. 2026-06-05 22:45 UTCEPSS rescore
  30. 2026-06-05 06:09 UTCEPSS rescore
  31. 2026-06-05 06:09 UTCEPSS rescore
  32. 2026-06-04 13:10 UTCEPSS rescore
  33. 2026-06-04 13:10 UTCEPSS rescore
  34. 2026-06-02 20:11 UTCEPSS rescore
  35. 2026-06-02 20:11 UTCEPSS rescore
  36. 2026-06-01 13:50 UTCEPSS rescore
  37. 2026-06-01 13:50 UTCEPSS rescore
  38. 2026-05-31 22:29 UTCEPSS rescore
  39. 2026-05-31 22:29 UTCEPSS rescore
  40. 2026-05-31 00:15 UTCEPSS rescore
  41. 2026-05-31 00:15 UTCEPSS rescore
  42. 2026-05-29 13:42 UTCEPSS rescore
  43. 2026-05-29 13:42 UTCEPSS rescore
  44. 2026-05-28 13:43 UTCEPSS rescore
  45. 2026-05-28 13:43 UTCEPSS rescore
  46. 2026-05-27 13:39 UTCEPSS rescore
  47. 2026-05-27 13:39 UTCEPSS rescore
  48. 2026-05-27 13:39 UTCEPSS rescore
  49. 2026-05-26 13:42 UTCEPSS rescore
  50. 2026-05-26 13:20 UTCEG score recompute
  51. 2026-05-26 13:20 UTCVendor advisory
  52. 2026-05-26 13:20 UTCEG score recompute
  53. 2026-05-26 13:20 UTCVendor advisory
  54. 2026-05-26 13:20 UTCGHSA enrichment
  55. 2026-05-26 13:20 UTCGHSA enrichment
  56. 2026-05-26 07:17 UTCEPSS rescore
  57. 2026-05-26 07:17 UTCEPSS rescore
  58. 2026-05-26 07:17 UTCEPSS rescore

Publicly available exploits

(4 references)

Working exploit code is in the public domain (4 GitHub PoCs). Defenders should treat patch urgency accordingly — public PoCs typically lead to mass-exploitation within 24-72 hours.

  • GitHub PoCChrisTheCoolHut/CVE-2021-33909
    First seen Sep 2, 2021

    CVE-2021-33909 Sequoia

    Open source ↗
  • GitHub PoCbbinfosec43/CVE-2021-33909
    First seen Jul 26, 2021

    Exploit code for CVE-2021-33909,Just a dump of removed https://github.com/AmIAHuman/ repo

    Open source ↗
  • GitHub PoCLiang2580/CVE-2021-33909
    First seen Jul 21, 2021

    Sequoia exploit (7/20/21)

    Open source ↗
  • GitHub PoCbaerwolf/cve-2021-33909
    First seen Jul 21, 2021

    This module fixes an issue in the kernels filesystem layer (CVE-2021-33909) by kprobe-replacing vulnerable functions during runtime

    Open source ↗

Related CVEs(same vendor + same CWE)

Frequently asked(5)

What is CVE-2021-33909?
CVE-2021-33909 is a high vulnerability published on July 20, 2021. fs/seq_file.c in the Linux kernel 3.16 through 5.13.x before 5.13.4 does not properly restrict seq buffer allocations, leading to an integer overflow, an Out-of-bounds Write, and escalation to root by an unprivileged user, aka CID-8cae8cd89f05.
When was CVE-2021-33909 disclosed?
CVE-2021-33909 was first published in the National Vulnerability Database on July 20, 2021, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-33909 actively exploited?
CVE-2021-33909 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 95.0% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-33909?
CVE-2021-33909 has a CVSS v3 base score of 7.8 (NVD).
How do I remediate CVE-2021-33909?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-33909, 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

Explore the affected products and dependency analysis for CVE-2021-33909

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