CVE-2021-22991 F5 BIG-IP Traffic Management Microkernel Buffer Overflow
The Traffic Management Microkernel of BIG-IP ASM Risk Engine has a buffer overflow vulnerability, leading to a bypassing of URL-based access controls.
From the CISA KEV catalogue version 2026.11.06, with Cybergen analysis. Updated 6 Nov 2026.
Should You Worry?
- CISA confirmed exploitation in the wild and added it to the Known Exploited Vulnerabilities catalogue on 18 Jan 2022.
- Rated Critical severity (CVSS 9.8, scored by CISA).
- This product type is often exposed to the internet, which is where attackers scan for it first.
- It has been in the catalogue for 1,753 days. Systems still unpatched now have almost certainly been scanned for it.
What It Is
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 Versions
| Product | Versions |
|---|---|
| BIG-IP | 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 |
From the public CVE record, as supplied by the vendor. Always confirm against the vendor advisory.
What To Do Now
- 1
Find it
Search your asset inventory and external attack surface for F5 BIG-IP Traffic Management Microkernel. Include cloud images, appliances and anything a supplier runs for you.
Attack Surface Management - 2
- 3
Hunt for compromise
If an affected system was reachable before you patched, assume it may have been hit. Check logs, new accounts, web shells and outbound connections from the date of exposure.
Incident Response - 4
Prove it is fixed
Rescan or test the system after patching. Upgrades that fail silently and forgotten secondary instances are common.
Penetration Testing
Vendor Advisories
The Compliance Clock
General guidance, not legal advice. Your obligations depend on your sector, scope and jurisdiction.
Not Sure If You Are Exposed?
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