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
9.8
EchelonGraph verdictPatch nowTreat as an emergency — this is being exploited.
  • Actively exploited in the wild (CISA-KEV)
CISA-KEV: ExploitedEPSS: 61%CVSS: 9.8Exploit: NoneExposed: 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)
EPSS
99.1%
KEV
⚠ Exploited

Published

March 31, 2021

Last Modified

October 27, 2025

Advisory Details (2)

Auto-updated Jun 1, 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 53× in last 7d / 210× 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 376 total refreshes for this CVE.

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