How severe is CVE-2025-53521?

CVE-2025-53521 has a CVSS score of 9.8/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2025-53521?

Affected package information for CVE-2025-53521 is not yet fully mapped. Check the official advisory links for details.

How do I fix CVE-2025-53521?

No fixed version has been published for CVE-2025-53521 yet. Monitor the advisory for updates, apply mitigations recommended by the vendor, and use O3 Security to track when a fix becomes available in your stack.

Is CVE-2025-53521 actively exploited in the wild?

No public exploit code has been indexed for CVE-2025-53521 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2025-53521?

CVE-2025-53521 has an EPSS (Exploit Prediction Scoring System) score of 8.8%, placing it in the 93th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

Is CVE-2025-53521 in the CISA Known Exploited Vulnerabilities catalog?

Yes. CVE-2025-53521 (F5 BIG-IP Stack-Based Buffer Overflow Vulnerability) was added to CISA's Known Exploited Vulnerabilities (KEV) catalog on 2026-03-27. CISA required all US federal civilian agencies to remediate this vulnerability by 2026-03-30. The required action was: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable. Being listed in the KEV catalog is the strongest possible confirmation of active exploitation — treat this as a critical priority.

What type of vulnerability is CVE-2025-53521?

CVE-2025-53521 is classified as CWE-121 (CWE-121). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

Which products and versions are affected by CVE-2025-53521?

CVE-2025-53521 affects f5 big-ip access policy manager. Check the affected-products list on this page against your deployed version to confirm exposure.

When was CVE-2025-53521 published, and has it been updated?

CVE-2025-53521 was published on October 15, 2025 and was last updated on April 2, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

CISA KEV·Added 2026-03-27 — agencies required to remediate by 2026-03-30

CVE-2025-53521

CRITICAL

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…

Published

Oct 15, 2025

Updated

Apr 2, 2026

Affected

0 pkgs

Patched

None yet

Exploits

None indexed

EPSS Exploitation Probability

via FIRST.org ↗

8.8%probability of exploitation in next 30 days

Lower Risk93th percentile0.00%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

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

1 product · 4 configurations

Application

big-ip access policy managerf5

≥ 17.5.0 && < 17.5.1.3

range

Frequently Asked Questions

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.

O3 Security · Impact-Aware SCA

Is CVE-2025-53521 in your stack?

O3 detects CVE-2025-53521 across dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

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