How severe is CVE-2021-22991?

CVE-2021-22991 has a CVSS score of 9.8/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-22991?

Affected package information for CVE-2021-22991 is not yet fully mapped. Check the official advisory links for details.

How do I fix CVE-2021-22991?

No fixed version has been published for CVE-2021-22991 yet. Monitor the advisory for updates, apply mitigations recommended by the vendor, and use O3 Security to track when a fix becomes available in your stack.

Is CVE-2021-22991 actively exploited in the wild?

Yes. There are 3 known exploit references for CVE-2021-22991, including 3 in-the-wild exploitations observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-22991?

CVE-2021-22991 has an EPSS (Exploit Prediction Scoring System) score of 73.1%, placing it in the 99th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. A score above 50% indicates significantly elevated exploitation risk — immediate patching is strongly recommended.

Is CVE-2021-22991 in the CISA Known Exploited Vulnerabilities catalog?

Yes. CVE-2021-22991 (F5 BIG-IP Traffic Management Microkernel Buffer Overflow) was added to CISA's Known Exploited Vulnerabilities (KEV) catalog on 2022-01-18. CISA required all US federal civilian agencies to remediate this vulnerability by 2022-02-01. The required action was: Apply updates per vendor instructions. Being listed in the KEV catalog is the strongest possible confirmation of active exploitation — treat this as a critical priority.

What type of vulnerability is CVE-2021-22991?

CVE-2021-22991 is classified as Buffer Overflow (CWE-119). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

Which products and versions are affected by CVE-2021-22991?

CVE-2021-22991 affects f5 big-ip access policy manager; f5 big-ip advanced firewall manager; f5 big-ip advanced web application firewall; f5 big-ip analytics, and 10 more product(s). Check the affected-products list on this page against your deployed version to confirm exposure.

When was CVE-2021-22991 published, and has it been updated?

CVE-2021-22991 was published on March 31, 2021 and was last updated on October 27, 2025. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

CISA KEV·Added 2022-01-18 — agencies required to remediate by 2022-02-01

CVE-2021-22991

CRITICAL

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…

Published

Mar 31, 2021

Updated

Oct 27, 2025

Affected

0 pkgs

Patched

None yet

Exploits

3 known

EPSS Exploitation Probability

via FIRST.org ↗

73.1%probability of exploitation in next 30 days

Very High Risk99th percentile0.00%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Description

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

14 products · 70 configurations

Application

big-ip access policy managerf5

≥ 16.0.0 && < 16.0.1.1

range

Application

big-ip advanced firewall managerf5

≥ 16.0.0 && < 16.0.1.1

range

Application

big-ip advanced web application firewallf5

≥ 16.0.0 && < 16.0.1.1

range

Application

big-ip analyticsf5

≥ 16.0.0 && < 16.0.1.1

range

Application

big-ip application acceleration managerf5

≥ 16.0.0 && < 16.0.1.1

range

Application

big-ip application security managerf5

≥ 16.0.0 && < 16.0.1.1

range

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

On BIG-IP versions 16.0.x before 16.0.1.1, 15.1.x before 15.1.2.1, 14.1.…

packetstormsecurity.comAPIMar 2021

On BIG-IP versions 16.0.x before 16.0.1.1, 15.1.x before 15.1.2.1, 14.1.…

unit42.paloaltonetworks.comAPIJul 2021

On BIG-IP versions 16.0.x before 16.0.1.1, 15.1.x before 15.1.2.1, 14.1.…

cisa.govCISAJan 2022

Frequently Asked Questions

O3 Security · Impact-Aware SCA

Is CVE-2021-22991 in your stack?

O3 detects CVE-2021-22991 across dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

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