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 products 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 patch CVE-2025-53521?

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.

How do I detect CVE-2025-53521 across my infrastructure?

Inventory every f5 big-ip access policy manager deployment and check each version against the affected-products list above. Because the exploit targets the running system rather than your application code, also watch for remote code execution at the network and runtime layer — O3 flags the exploit behaviour from runtime telemetry and egress traffic even before a vulnerable build is confirmed.

How do I mitigate CVE-2025-53521 if there is no patch (or I can't update yet)?

Cut exposure now: restrict the management/admin interface to trusted networks, segment the device, and apply the vendor's recommended configuration mitigations and any WAF/IPS signature. O3's runtime protection blocks the exploit chain at execution, holding the line on unpatched or end-of-life systems until you can patch.

How does O3 Security protect against CVE-2025-53521?

O3 detects and blocks CVE-2025-53521 exploitation at runtime: eBPF exploit-chain detection, plus L7 egress monitoring that catches the post-exploitation callback and severs the attacker's outbound channel.

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 2.2%, placing it in the 81th 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 June 17, 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

Jun 17, 2026

Affected

0 pkgs

Patched

None yet

Exploits

None indexed

EPSS Exploitation Probability

via FIRST.org ↗

2.2%probability of exploitation in next 30 days

Lower Risk81th percentile-0.03%

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

Detection & mitigation playbook

Vendor / appliance

Detect
Inventory every f5 big-ip access policy manager deployment and check each version against the affected-products list above. Because the exploit targets the running system rather than your application code, also watch for remote code execution at the network and runtime layer — O3 flags the exploit behaviour from runtime telemetry and egress traffic even before a vulnerable build is confirmed.
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
Cut exposure now: restrict the management/admin interface to trusted networks, segment the device, and apply the vendor's recommended configuration mitigations and any WAF/IPS signature. O3's runtime protection blocks the exploit chain at execution, holding the line on unpatched or end-of-life systems until you can patch.
How O3 protects you
O3 detects and blocks CVE-2025-53521 exploitation at runtime: eBPF exploit-chain detection, plus L7 egress monitoring that catches the post-exploitation callback and severs the attacker's outbound channel.

Tailored to CVE-2025-53521. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

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 · Runtime Protection

Is CVE-2025-53521 being exploited in your environment?

O3's eBPF runtime sensors and L7 egress monitoring detect and block the CVE-2025-53521 exploit chain at execution — protecting unpatched and end-of-life systems until the vendor patch is applied.

Protect my workloads How runtime protection works