Background exploitation KEV catalog No authentication
CVE-2021-22991

F5 BIG-IP Traffic Management Microkernel Buffer Overflow

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…

CheckOps priority index
8.2/10 Patch within 24 h
Severity9.8
Probability6.2
Exploitation4/5

Severity = CVSS. Probability = EPSS (FIRST). Exploitation = public signals: KEV, EUVD, ransomware, EPSS above 10 %, no account required.

EPSS · today 62.4% higher than 99.2% of CVEs
CVSS 3.1 9.8 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:
Exploited for 1,750 days 18 Jan 2022
CISA due date 01 Feb 2022 for US federal agencies

Exploitation probability EPSS · FIRST

05010026 Sep05 Oct15 Oct24 Oct02 Nov
EPSS probability (%)Percentile among all CVEs

Exploitation signals 4 / 5

  • KEV catalog (CISA)18 Jan 2022
  • Exploited in EUVD (ENISA)18 Jan 2022
  • Used by ransomwareno
  • EPSS above 10 %62.4%
  • No account, over the networkyes

What to do

Fix

Apply the vendor’s fix as soon as it is available.

CISA guidance: Apply updates per vendor instructions.

Meanwhile

Take the service off the internet or restrict access to it, watch the logs and look for signs of compromise.

Manufacturers (CRA)

Exploited vulnerability in your product: early warning to ENISA within 24 h, then notification within 72 h (Article 14 of the Cyber Resilience Act). The CRA explained

Description ENISA EUVD

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.

Affected products

BIG-IPBIG-IP Traffic Management Microkernel
Affected 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, 12.1.x before 12.1.5.3
Weaknesses (CWE)

Open source packages OSV

Affected libraries according to OSV, with fixed versions.

Timeline

  1. Published

  2. Exploitation reported (ENISA)

  3. Added to the KEV catalog

  4. CISA remediation due date

  5. EPSS peak: 62.4%

References

Other exploited vulnerabilities from the same vendor

  • CVE-2026-94127F5 BIG-IP APM Heap-based Buffer Overflow Vulnerability
    6.9 · Actively exploited
  • CVE-2025-53521F5 BIG-IP Stack-Based Buffer Overflow Vulnerability
    5.6 · Background exploitation
  • CVE-2023-46748F5 BIG-IP Configuration Utility SQL Injection Vulnerability
    4.8 · Background exploitation
  • CVE-2023-46747F5 BIG-IP Configuration Utility Authentication Bypass Vulnerability
    9.8 · Background exploitation
  • CVE-2022-1388F5 BIG-IP Missing Authentication Vulnerability
    9.9 · Background exploitation
  • CVE-2021-22986F5 BIG-IP and BIG-IQ Centralized Management iControl REST Remote Code Execution Vulnerability
    9.9 · Background exploitation

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Sources: CISA KEV · ENISA EUVD · FIRST EPSS · OSV. Public data aggregated by CheckOps, updated automatically. Source texts remain the property of their authors. All exploited vulnerabilities