CVE-2025-53521 — Big-Ip Access Policy Manager
CRITICALCVE-2025-53521 is a critical-severity (CVSS 9.8) CWE-121 vulnerability in f5 big-ip access policy manager. It is in CISA's Known Exploited Vulnerabilities catalog (added 2026-03-27) — treat it as actively exploited and patch now. A fix is available — see the affected versions and patch details below.
When a BIG-IP APM access policy is configured on a virtual server, specific malicious traffic can lead to Remote Code Execution (RCE). Note: Software versions which have reached…
Exploitation Status
Actively exploited in the wild
- Confirmed by CISA's Known Exploited Vulnerabilities catalog on 2026-03-27. Federal agencies were required to remediate by 2026-03-30.
- 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-2025-53521.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2025-53521 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 395,249 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Description
When a BIG-IP APM access policy is configured on a virtual server, specific malicious traffic can lead to Remote Code Execution (RCE).
Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.
Affected Products
big-ip access policy managerf5Detection & mitigation playbook
Vendor / applianceDetect
Inventory every f5 big-ip access policy manager deployment and check each version against the affected-products list above.
Fix
Apply the f5 big-ip access policy manager security patch or hotfix for CVE-2025-53521 on the affected version, following the vendor advisory for your exact build.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands. Alongside that, restrict the management interface to trusted networks and apply the vendor's recommended configuration mitigations.
Frequently Asked Questions
Is CVE-2025-53521 being exploited in your environment?
Detect and block the exploit chain at execution, on systems you cannot patch yet.