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% (45th percentile of EPSS-scored CVEs). 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: 0.6%CVSS: 7.8Exploit: None knownExposed services: Not assessed

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
7.8HIGHmedium confidence
EG Risk
40
EG Risk 40/100CISA SSVC

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%
CISA SSVC: Track at low or medium mission impact; Track or Attend at high (mission-essential systems).
Action: A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.
EPSS PROB
0.6%
EPSS %ILE
45th
KEV
Not listed

CISA SSVCTrack at low or medium mission impact; Track or Attend at high (mission-essential systems).

A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.

Exploitation none (no KEV listing, exploit record or EPSS ≥ 50%) · Automatable unknown (not published for this CVE) · Technical impact partial (CVSS below 9.0). Mission impact is CISA's Mission & Well-being decision point, and only you can judge it: high means the affected system is essential to your organisation's mission, or its compromise could cause irreversible harm to people. CISA's decision table

Published

May 14, 2021

Last Modified

August 5, 2026

Advisory Details (6)

Auto-updated Aug 5, 2026
⚠️ Active exploitation confirmed. Patch available.
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(6)

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 / EcosystemFix (by version range) / 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 rangeFix by version rangeDependents
linux—
  • every version up to 5.10.24-1: fixed in 5.10.24-1
—
Debian:12(1)
PackageVulnerable rangeFix by version rangeDependents
linux—
  • every version up to 5.10.24-1: fixed in 5.10.24-1
—
Debian:13(1)
PackageVulnerable rangeFix by version rangeDependents
linux—
  • every version up to 5.10.24-1: fixed in 5.10.24-1
—
Debian:14(1)
PackageVulnerable rangeFix by version rangeDependents
linux—
  • every version up to 5.10.24-1: fixed in 5.10.24-1
—
Debian:9(1)
PackageVulnerable rangeFix by version rangeDependents
linux4.9.107-1 ... 4.9.88-1~bpo8+1 (69 versions)
  • every version up to 4.9.303-1: fixed in 4.9.303-1
—

Weakness Classification(1)

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

Additional Vendor Advisories

(3)

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 7× in last 7d / 34× 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 187 total refreshes for this CVE.

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

Related CVEs(same product + 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 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 0.6% probability of exploitation in the next 30 days (45th percentile of EPSS-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?
A fix for CVE-2021-33033 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2021-33033 are linked in the Vendor Advisories panel on this page.

Dependency Blast Radius

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