CVE-2021-22991

CRITICALNVD 9.89.8—
EchelonGraph scoreHIGH confidence

Score elevated to 9.8 because this CVE is listed on the CISA Known Exploited Vulnerabilities catalog (added 2022-01-18), indicating real-world exploitation has been confirmed by US federal agencies. NVD baseline CVSS 9.8 retained for reference. Confidence: HIGH.

Triggered by: CISA KEV (actively exploited)
Sources: cisa_kev, epss, ghsa, nvd
Trending — 4 sources updated this weekExploited in the wild
9.8EG
EchelonGraph verdictPatch nowTreat as an emergency — this is being exploited.
  • Actively exploited in the wild (CISA-KEV)
CISA-KEV: ExploitedEPSS PROB: 61%CVSS: 9.8Exploit: cisa kev · ssvc active · epss top5pct · epss highExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

On BIG-IP versions 16.0.x before 16.0.1.1, 15.1.x before 15.1.2.1, 14.1.x before 14.1.4, 13.1.x before 13.1.3.6, and 12.1.x before 12.1.5.3, undisclosed requests to a virtual server may be incorrectly handled by the Traffic Management Microkernel (TMM) URI normalization, which may trigger a buffer overflow, resulting in a DoS attack. In certain situations, it may theoretically allow bypass of URL based access control or remote code execution (RCE). Note: Software versions which have reached End of Software Development (EoSD) are not evaluated.

CVSS v3
9.8
EG Score
9.8(high)
EG Risk
99(Act)
EG Risk 99/100SSVC: Act

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
Severity98% × 45%
Exploitation100% × 40%
Automatability100% × 15%
Action: Fix now — active exploitation, automatable, high impact.
EPSS PROB
61%
EPSS %ILE
99%
KEV
⚠ Exploited

Published

March 31, 2021

Last Modified

October 27, 2025

Advisory Details (2)

Auto-updated Sep 17, 2026
⚠️ Active exploitation confirmed. Patch available. Sources: cisa.
cisa Patch Available🔴 Active Exploitation

Known Exploited Vulnerabilities Catalog | CISA

Known Exploited Vulnerabilities Catalog | CISA. Listed in CISA Known Exploited Vulnerabilities catalog.

https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-22991
generic

myF5

https://support.f5.com/csp/article/K56715231

Weakness Classification(3)

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

Data Freshness Timeline

(refreshed 52× in last 7d / 225× 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 814 total refreshes for this CVE.

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

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Frequently asked(6)

What is CVE-2021-22991?
CVE-2021-22991 is a critical vulnerability published on March 31, 2021. On BIG-IP versions 16.0.x before 16.0.1.1, 15.1.x before 15.1.2.1, 14.1.x before 14.1.4, 13.1.x before 13.1.3.6, and 12.1.x before 12.1.5.3, undisclosed requests to a virtual server may be incorrectly handled by the Traffic Management Microkernel (TMM) URI normalization, which may trigger a buffer…
When was CVE-2021-22991 disclosed?
CVE-2021-22991 was first published in the National Vulnerability Database on March 31, 2021, with the most recent update on October 27, 2025. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-22991 actively exploited?
Yes. CISA added CVE-2021-22991 to the Known Exploited Vulnerabilities catalog on January 18, 2022, affecting F5 BIG-IP Traffic Management Microkernel. KEV listing indicates confirmed exploitation in the wild; this CVE warrants immediate patching attention.
What is the CVSS score of CVE-2021-22991?
CVE-2021-22991 has a CVSS v3 base score of 9.8 (NVD).
Which products are affected by CVE-2021-22991?
CVE-2021-22991 affects F5 BIG-IP Traffic Management Microkernel. 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-2021-22991?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-22991, 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.

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