CVE-2021-22991
CRITICALCVE-2021-22991 is a critical-severity (CVSS 9.8) Buffer Overflow vulnerability. It is in CISA's Known Exploited Vulnerabilities catalog (added 2022-01-18) — treat it as actively exploited and patch now. No vendor fix is recorded yet; mitigation options are listed below.
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…
Exploitation Status
Actively exploited in the wild
- Confirmed by CISA's Known Exploited Vulnerabilities catalog on 2022-01-18. Federal agencies were required to remediate by 2022-02-01.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA (KEV catalog and SSVC triage) for CVE-2021-22991.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-22991 by exploitation likelihood (EPSS) against impact (CVSS). In the shaded patch-first corner (EPSS 50%+, CVSS 7.0+).
Where this sits among everything scored
Of 395,249 CVEs with a current EPSS score, this one falls in the 50–90% band (highlighted). Counts from FIRST.org, log-scaled.
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
big-ip access policy managerf5big-ip advanced firewall managerf5big-ip advanced web application firewallf5big-ip analyticsf5big-ip application acceleration managerf5big-ip application security managerf5Research 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.…
On BIG-IP versions 16.0.x before 16.0.1.1, 15.1.x before 15.1.2.1, 14.1.…
On BIG-IP versions 16.0.x before 16.0.1.1, 15.1.x before 15.1.2.1, 14.1.…
Detection & mitigation playbook
VulnerabilityDetect
Identify every host running the affected component and compare the installed build against the fixed version below — for source-built or distro-packaged software the version string, not a lockfile, is the source of truth (`dpkg -l`, `rpm -q`, or the binary's own `--version`).
Remediation status
No fixed release is recorded for CVE-2021-22991 yet. Track the upstream advisory, and apply the exposure-reduction steps below in the meantime.
Mitigate without a patch
Constrain what reaches the vulnerable code: limit the size and shape of untrusted input, isolate the affected component in a sandboxed or least-privileged process, and enable the platform's memory-safety mitigations (ASLR, stack protector, hardened allocator) so an out-of-bounds access is more likely to fail closed than to be exploitable.
Frequently Asked Questions
Is CVE-2021-22991 in your dependencies?
Find it across , including transitive dependencies.