CVE-2021-33033

HIGHNVD 7.87.8—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 7.8 under NVD CVSS v3. EPSS exploit probability: 0.6%, top 56% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
7.8EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 1%CVSS: 7.8Exploit: None knownExposed: 0

A fix is available — apply it.

The Linux kernel before 5.11.14 has a use-after-free in cipso_v4_genopt in net/ipv4/cipso_ipv4.c because the CIPSO and CALIPSO refcounting for the DOI definitions is mishandled, aka CID-ad5d07f4a9cd. This leads to writing an arbitrary value.

CVSS v3
7.8
EG Score
7.8(medium)
EG Risk
40(Track)
EG Risk 40/100SSVC: Track

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
Severity78% × 45%
Exploitation1% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
1%
EPSS %ILE
45%
KEV
Not listed

Published

May 14, 2021

Last Modified

August 5, 2026

Advisory Details (6)

Auto-updated Aug 5, 2026
⚠️ Active exploitation confirmed. No patch confirmed yet.
generic

cipso,calipso: resolve a number of problems with the DOI refcounts - kernel/git/torvalds/linux.git - Linux kernel source tree

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ad5d07f4a9cd671233ae20983848874731102c08
generic

net: mac802154: Fix general protection fault - kernel/git/torvalds/linux.git - Linux kernel source tree

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=1165affd484889d4986cf3b724318935a0b120d8
generic🔴 Active Exploitation
https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.11.7
generic
https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.11.14
generic

KASAN: use-after-free Read in cipso_v4_genopt

https://syzkaller.appspot.com/bug?id=96e7d345748d8814901c91cd92084ed04b46701e
generic

SyzScope - KASAN: use-after-free Read in cipso_v4_genopt

https://sites.google.com/view/syzscope/kasan-use-after-free-read-in-cipso_v4_genopt

Vendor Advisories for CVE-2021-33033(5)

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

Patch Availability(7)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntulinux-image-virtual-hwe-20.04-edge (5.8.0.55.60) @ groovy2026-05-26ubuntu
ubuntulinux-image-azure (4.15.0.1115.88) @ trusty2026-05-26ubuntu
ubuntulinux-image-lowlatency (4.4.0.222.229) @ xenial2026-05-26ubuntu
redhatkernel-rt-0:4.18.0-348.rt7.130.el82021-11-09redhat
redhatkernel-0:4.18.0-348.el82021-11-09redhat
redhatkernel-0:3.10.0-1160.36.2.el72021-07-21redhat
redhatkernel-rt-0:3.10.0-1160.36.2.rt56.1179.el72021-07-21redhat

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

(5 across 5 ecosystems)
Debian:11(1)
PackageVulnerable rangeFixed inDependents
linux—5.10.24-1—
Debian:12(1)
PackageVulnerable rangeFixed inDependents
linux—5.10.24-1—
Debian:13(1)
PackageVulnerable rangeFixed inDependents
linux—5.10.24-1—
Debian:14(1)
PackageVulnerable rangeFixed inDependents
linux—5.10.24-1—
Debian:9(1)
PackageVulnerable rangeFixed inDependents
linux4.9.107-1 ... 4.9.88-1~bpo8+1 (69 versions)4.9.303-1—

Weakness Classification(1)

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

Additional Vendor Advisories

(4)

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 9× in last 7d / 40× 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 137 total refreshes for this CVE.

  1. 2026-08-21 03:53 UTCOSV refresh
  2. 2026-08-20 22:52 UTCEPSS rescore
  3. 2026-08-19 17:01 UTCEPSS rescore
  4. 2026-08-18 13:45 UTCEPSS rescore
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  17. 2026-08-05 19:14 UTCEPSS rescore
  18. 2026-08-05 18:50 UTCEG score recompute
  19. 2026-08-05 18:50 UTCVendor advisory
  20. 2026-08-05 18:50 UTCGHSA enrichment
  21. 2026-08-04 21:48 UTCOSV refresh
  22. 2026-08-04 15:06 UTCEPSS rescore
  23. 2026-08-04 10:34 UTCEPSS rescore
  24. 2026-08-03 10:33 UTCEPSS rescore
  25. 2026-08-02 02:24 UTCEPSS rescore
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  1. 2026-08-02 02:24 UTCEPSS rescore
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  10. 2026-07-23 14:16 UTCEPSS rescore
  11. 2026-07-23 14:16 UTCEPSS rescore
  12. 2026-07-23 02:01 UTCEG score recompute
  13. 2026-07-22 22:48 UTCEG score recompute
  14. 2026-07-22 14:06 UTCEPSS rescore
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  21. 2026-07-19 02:27 UTCEPSS rescore
  22. 2026-07-18 19:59 UTCOSV refresh
  23. 2026-07-18 10:02 UTCEPSS rescore
  24. 2026-07-18 10:02 UTCEPSS rescore
  25. 2026-07-16 17:00 UTCEPSS rescore
  26. 2026-07-16 17:00 UTCEPSS rescore
  27. 2026-07-15 16:55 UTCEPSS rescore
  28. 2026-07-15 01:58 UTCEPSS rescore
  29. 2026-07-13 22:27 UTCEPSS rescore
  30. 2026-07-13 06:10 UTCEPSS rescore
  31. 2026-07-12 05:44 UTCEPSS rescore
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  44. 2026-07-01 15:04 UTCEPSS rescore
  45. 2026-07-01 03:18 UTCOSV refresh
  46. 2026-06-30 23:20 UTCEPSS rescore
  47. 2026-06-30 23:20 UTCEPSS rescore
  48. 2026-06-29 14:04 UTCEPSS rescore
  49. 2026-06-28 14:05 UTCEPSS rescore
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  66. 2026-06-18 17:51 UTCEPSS rescore
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  68. 2026-06-17 17:51 UTCEPSS rescore
  69. 2026-06-16 17:51 UTCEPSS rescore
  70. 2026-06-16 17:51 UTCEPSS rescore
  71. 2026-06-15 17:46 UTCEPSS rescore
  72. 2026-06-14 23:15 UTCEPSS rescore
  73. 2026-06-13 22:58 UTCEPSS rescore
  74. 2026-06-13 22:58 UTCEPSS rescore
  75. 2026-06-13 05:43 UTCOSV refresh

Related CVEs(same vendor + same CWE)

Frequently asked(5)

What is CVE-2021-33033?
CVE-2021-33033 is a high vulnerability published on May 14, 2021. The Linux kernel before 5.11.14 has a use-after-free in cipsov4genopt in net/ipv4/cipso_ipv4.c because the CIPSO and CALIPSO refcounting for the DOI definitions is mishandled, aka CID-ad5d07f4a9cd. This leads to writing an arbitrary value.
When was CVE-2021-33033 disclosed?
CVE-2021-33033 was first published in the National Vulnerability Database on May 14, 2021, with the most recent update on August 5, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-33033 actively exploited?
CVE-2021-33033 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 1% probability of exploitation in the next 30 days, which ranks it in the top 55.4% of all scored CVEs.
What is the CVSS score of CVE-2021-33033?
CVE-2021-33033 has a CVSS v3 base score of 7.8 (NVD).
How do I remediate CVE-2021-33033?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-33033, 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-2021-33033

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