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Vulnerabilities

Vulnerability · CVE-2021-22991

F5 BIG-IP Traffic Management Microkernel Buffer Overflow

Published Mar 31, 2021 · catalog updated Jun 16, 2026 · F5 BIG-IP Traffic Management Microkernel

Patch now

CVE-2021-22991 is in the CISA known-exploited catalog, due Feb 1, 2022. Confirm F5 BIG-IP Traffic Management Microkernel against the vendor advisory and apply that fix. The CVSS score does not change the priority.

Gaps on this record

  • No version range is stored. A customer cannot check an installed version against this record.
Severity
Critical9.8
Known exploitation
CISA KEV and VulnCheck KEV
EPSS
61.06%
Remediation
Remediation guidance
Affected products
cpe f5/big-ip access policy manager · cpe f5/big-ip advanced firewall manager · vendor F5 BIG-IP Traffic Management Microkernel

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.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe f5/big-ip access policy managerversion unspecified
  • cpe f5/big-ip advanced firewall managerversion unspecified
  • vendor F5 BIG-IP Traffic Management Microkernelversion unspecified

How to fix CVE-2021-22991

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

CVE-2021-22991 is in the CISA known-exploited catalog, due Feb 1, 2022. Confirm F5 BIG-IP Traffic Management Microkernel against the vendor advisory and apply that fix. The CVSS score does not change the priority.

Which versions are affected?

Affected version ranges are not on this record. Apply updates per vendor instructions.

What should an analyst verify?

CWE-119: Buffer Overflow. EPSS 61.06%. The CISA KEV listing is the exploitation evidence. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Mar 31, 2021 · Catalog

    Detected

    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

  2. Jan 18, 2022 · CISA KEV

    Known exploited

    Apply updates per vendor instructions.

  3. Feb 1, 2022 · CISA KEV

    Remediation due

    Apply updates per vendor instructions.

  4. Jun 16, 2026 · Catalog

    Updated

    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

Sources

  • CISA KEVConfirmed exploitationCVE-2021-22991

    The Traffic Management Microkernel of BIG-IP ASM Risk Engine has a buffer overflow vulnerability, leading to a bypassing of URL-based access controls.

    cisa.gov
  • CVE.orgVulnerability recordCVE-2021-22991

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2021-22991

    30-day exploitation probability 61.1%

    first.org
  • NIST NVDVulnerability recordCVE-2021-22991

    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 ma

    nvd.nist.gov
  • VulnCheck KEVConfirmed exploitationCVE-2021-22991

    The Traffic Management Microkernel of BIG-IP ASM Risk Engine has a buffer overflow vulnerability, leading to a bypassing of URL-based access controls.

    vulncheck.com

References

Freshness

Last verified in this catalog Oct 17, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.