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Actively exploited in the wild. This CVE is on the CISA Known Exploited Vulnerabilities list — treat remediation as urgent. Federal remediation due by 1 Feb 2022.
Big Ip Access Policy ManagerApplication · F5

CVE-2021-22991

CRITICAL · 9.8 CVSS v3.1 Published 2021-03-31
Fix available
A fix is available. Upgrade to 12.1.5.3 / 13.1.3.6 or later.
See remediation →
100/100
Remediation priority · Urgent
In the wild High EPSS Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

A buffer overflow vulnerability exists in the F5 BIG-IP Traffic Management Microkernel (TMM) URI normalization component. Specifically, undisclosed requests to a virtual server are incorrectly handled during URI normalization, triggering a buffer overflow. This can cause denial of service and potentially allow URL-based access control bypass or remote code execution in certain conditions.

MitigationUpgrade BIG-IP to version 16.0.1.1, 15.1.2.1, 14.1.4, 13.1.3.6, or 12.1.5.3 or later. Alternatively, apply the relevant hotfix patch provided by F5.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Big Ip Access Policy ManagerApplication
Affected:>= 12.1.0, < 12.1.5.3>= 13.1.0, < 13.1.3.6>= 14.1.0, < 14.1.4>= 15.1.0, < 15.1.2.1>= 16.0.0, < 16.0.1.1
Big Ip Advanced Firewall ManagerApplication
Affected:>= 12.1.0, < 12.1.5.3>= 13.1.0, < 13.1.3.6>= 14.1.0, < 14.1.4>= 15.1.0, < 15.1.2.1>= 16.0.0, < 16.0.1.1
Big Ip Advanced Web Application FirewallApplication
Affected:>= 12.1.0, < 12.1.5.3>= 13.1.0, < 13.1.3.6>= 14.1.0, < 14.1.4>= 15.1.0, < 15.1.2.1>= 16.0.0, < 16.0.1.1
Big Ip AnalyticsApplication
Affected:>= 12.1.0, < 12.1.5.3>= 13.1.0, < 13.1.3.6>= 14.1.0, < 14.1.4>= 15.1.0, < 15.1.2.1>= 16.0.0, < 16.0.1.1
Big Ip Application Acceleration ManagerApplication
Affected:>= 12.1.0, < 12.1.5.3>= 13.1.0, < 13.1.3.6>= 14.1.0, < 14.1.4>= 15.1.0, < 15.1.2.1>= 16.0.0, < 16.0.1.1
Big Ip Application Security ManagerApplication
Affected:>= 12.1.0, < 12.1.5.3>= 13.1.0, < 13.1.3.6>= 14.1.0, < 14.1.4>= 15.1.0, < 15.1.2.1>= 16.0.0, < 16.0.1.1
Big Ip Ddos Hybrid DefenderApplication
Affected:>= 12.1.0, < 12.1.5.3>= 13.1.0, < 13.1.3.6>= 14.1.0, < 14.1.4>= 15.1.0, < 15.1.2.1>= 16.0.0, < 16.0.1.1
Big Ip Domain Name SystemApplication
Affected:>= 12.1.0, < 12.1.5.3>= 13.1.0, < 13.1.3.6>= 14.1.0, < 14.1.4>= 15.1.0, < 15.1.2.1>= 16.0.0, < 16.0.1.1

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify BIG-IP system version
    Run command 'tmsh show sys version' or check the BIG-IP Configuration utility under System > Software Management > ISO Image. Alternatively, run 'bigstart status' and review the version banner at login.
    Affected if The installed version falls within any of these ranges: 12.1.0 to 12.1.5.2, 13.1.0 to 13.1.3.5, 14.1.0 to 14.1.3, 15.1.0 to 15.1.2.0, or 16.0.0 to 16.0.1.0.
  2. Determine installed BIG-IP modules
    Run 'tmsh list sys module' or check System > Resource > Modules in the Configuration utility. Identify which of these modules are provisioned: Access Policy Manager, Advanced Firewall Manager, Advanced Web Application Firewall, Analytics, Application Acceleration Manager, Application Security Manager, DDoS Hybrid Defender, or Domain Name System.
    Affected if Any affected module is provisioned on a system with a vulnerable version.
  3. Verify virtual server exposure
    Run 'tmsh list ltm virtual' to list all configured virtual servers. Check the 'destination' and 'mask' addresses to determine if they accept external traffic. Review the 'profiles' applied to each virtual server.
    Affected if Virtual servers exist and are reachable via network paths that include the TMM processing path.
  4. Confirm TMM is active
    Run 'tmsh show ltm' to verify the Traffic Management Microkernel is running. Check 'tmsh show sys tmm' for TMM status and ensure the 'TMM' process is in a running state.
    Affected if TMM is active and processing traffic for virtual servers on a vulnerable version.

The environment is affected if the BIG-IP version is 12.1.0-12.1.5.2, 13.1.0-13.1.3.5, 14.1.0-14.1.3, 15.1.0-15.1.2.0, or 16.0.0-16.0.1.0 AND any of the affected modules (APM, AFM, AWM, Analytics, AAM, ASM, DDoS Hybrid Defender, DNS) are provisioned with active virtual servers.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 12.1.5.3 / 13.1.3.6 / 14.1.4 or later
Fixed in 12.1.5.313.1.3.614.1.4
Interim mitigation

Upgrade BIG-IP to version 16.0.1.1, 15.1.2.1, 14.1.4, 13.1.3.6, or 12.1.5.3 or later. Alternatively, apply the relevant hotfix patch provided by F5.

Recommended fix High confidence

Upgrade to 12.1.5.3, 13.1.3.6, 14.1.4, or 15.1.2.1 (or 16.0.1.1 if on 16.0.x)

  1. 1. Identify the current BIG-IP version by running `tmsh show sys version` or checking the web management console.
  2. 2. Determine which BIG-IP module(s) (APM, AFM, AWAF, Analytics, AAM, ASM, DDoS Hybrid Defender, DNS) are deployed, as all are affected.
  3. 3. Backup the BIG-IP configuration using `tmsh save sys config` or via the web management console.
  4. 4. Download the appropriate hotfix from the F5 downloads page (support.f5.com) corresponding to your current major version: 12.1.5.3, 13.1.3.6, 14.1.4, or 15.1.2.1.
  5. 5. Upload and install the hotfix via `tmsh install sys software` or through the web management console under Software Management > ISO/Import.
  6. 6. Reboot the BIG-IP device to apply the update.
  7. 7. Verify the version after reboot using `tmsh show sys version` to confirm the patch level matches the fixed release.
  8. 8. Test critical applications and access policies to ensure normal operation.
Caveat Review F5 release notes for any changes to TMM behavior or URL normalization that may affect existing access policies or URL-based access control configurations

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Big Ip Access Policy Manager Exploited in the wild — priority engagement
  • Consultation8.0 h
  • Implementation12.0 h
  • Testing16.0 h
  • Review / QA8.0 h
44.0 hours of engineering $7,600
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-22991 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data