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Weekly Signal
Live intelligence Updated 21 Aug 2026 · 22:11 UTC

F5 · Big-ip Access Policy Manager, Big-ip Advanced Firewall Manager, Big-ip Advanced Web Application Firewall +12 more

CVE-2021-22991

F5 BIG-IP Traffic Management Microkernel Buffer Overflow

Recommended action

Validate affected assets and exposure now, then remediate on an accelerated schedule. F5 Security advisory K56715231

View response plan
CVSS9.8
EPSS61.1%
KEVYes
ExploitationConfirmed exploitation
RemediationNot yet verified ↓

Assessment

Why it matters

CISA lists this vulnerability as known to be exploited; exploitation is confirmed; EPSS is 61.1%; technical severity is CVSS 9.8.

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.

Who should care

  • Teams operating Big-ip Access Policy Manager, Big-ip Advanced Firewall Manager, Big-ip Advanced Web Application Firewall +12 more
  • Vulnerability and exposure management teams
  • Security operations teams monitoring exploitation activity

Response plan

What I would do

  1. Confirm whether Big-ip Access Policy Manager, Big-ip Advanced Firewall Manager, Big-ip Advanced Web Application Firewall +12 more is present in the environment.
  2. Identify affected versions and establish whether vulnerable services are exposed or reachable.
  3. F5 Security advisory K56715231
  4. Review relevant security telemetry for evidence of attempted or successful exploitation.
  5. Document the remediation decision and track it to verified completion.

Treatment intelligence

Remediation intelligence

Not yet verified

Vendor sources are listed before government and third-party guidance. Confirm product applicability and change prerequisites before deployment.

Verification noteAutomated link verification has not completed for this guidance yet.

Advisory

Required Action

Technical details

CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CWE
CWE-119
Affected versions
F5 Big-ip Access Policy Manager (Start Including 12.1.0, End Excluding 12.1.5.3 | Start Including 13.1.0, End Excluding 13.1.3.6 | Start Including 14.1.0, End Excluding 14.1.4 | Start Including 15.1.0, End Excluding 15.1.2.1); F5 Big-ip Advanced Firewall Manager (Start Including 12.1.0, End Excluding 12.1.5.3 | Start Including 13.1.0, End Excluding 13.1.3.6 | Start Including 14.1.0, End Excluding 14.1.4 | Start Including 15.1.0, End Excluding 15.1.2.1); F5 Big-ip Advanced Web Application Firewall (Start Including 12.1.0, End Excluding 12.1.5.3 | Start Including 13.1.0, End Excluding 13.1.3.6 | Start Including 14.1.0, End Excluding 14.1.4 | Start Including 15.1.0, End Excluding 15.1.2.1); F5 Big-ip Analytics (Start Including 12.1.0, End Excluding 12.1.5.3 | Start Including 13.1.0, End Excluding 13.1.3.6 | Start Including 14.1.0, End Excluding 14.1.4 | Start Including 15.1.0, End Excluding 15.1.2.1); F5 Big-ip Application Acceleration Manager (Start Including 12.1.0, End Excluding 12.1.5.3 | Start Including 13.1.0, End Excluding 13.1.3.6 | Start Including 14.1.0, End Excluding 14.1.4 | Start Including 15.1.0, End Excluding 15.1.2.1); F5 Big-ip Application Security Manager (Start Including 12.1.0, End Excluding 12.1.5.3 | Start Including 13.1.0, End Excluding 13.1.3.6 | Start Including 14.1.0, End Excluding 14.1.4 | Start Including 15.1.0, End Excluding 15.1.2.1); F5 Big-ip Ddos Hybrid Defender (Start Including 12.1.0, End Excluding 12.1.5.3 | Start Including 13.1.0, End Excluding 13.1.3.6 | Start Including 14.1.0, End Excluding 14.1.4 | Start Including 15.1.0, End Excluding 15.1.2.1); F5 Big-ip Domain Name System (Start Including 12.1.0, End Excluding 12.1.5.3 | Start Including 13.1.0, End Excluding 13.1.3.6 | Start Including 14.1.0, End Excluding 14.1.4 | Start Including 15.1.0, End Excluding 15.1.2.1)
Fixed versions
F5 Big-ip Access Policy Manager (Fixed from 12.1.5.3, 13.1.3.6, 14.1.4, 15.1.2.1, 16.0.1.1); F5 Big-ip Advanced Firewall Manager (Fixed from 12.1.5.3, 13.1.3.6, 14.1.4, 15.1.2.1, 16.0.1.1); F5 Big-ip Advanced Web Application Firewall (Fixed from 12.1.5.3, 13.1.3.6, 14.1.4, 15.1.2.1, 16.0.1.1); F5 Big-ip Analytics (Fixed from 12.1.5.3, 13.1.3.6, 14.1.4, 15.1.2.1, 16.0.1.1); F5 Big-ip Application Acceleration Manager (Fixed from 12.1.5.3, 13.1.3.6, 14.1.4, 15.1.2.1, 16.0.1.1); F5 Big-ip Application Security Manager (Fixed from 12.1.5.3, 13.1.3.6, 14.1.4, 15.1.2.1, 16.0.1.1); F5 Big-ip Ddos Hybrid Defender (Fixed from 12.1.5.3, 13.1.3.6, 14.1.4, 15.1.2.1, 16.0.1.1); F5 Big-ip Domain Name System (Fixed from 12.1.5.3, 13.1.3.6, 14.1.4, 15.1.2.1, 16.0.1.1)
Published
31 March 2021
Attack vector
Network
Privileges required
None
User interaction
None

Signal timeline

  1. CVE published
  2. Added to CISA KEV
  3. Latest EPSS score: 61.1%
  4. Signal calculated at 80

External references

Live public intelligence This assessment combines public-source evidence. Validate the affected product, version and exposure against your own environment before making a risk decision.