# CVE-2025-53521: F5 BIG-IP stack-based buffer overflow in APM

Source: https://junglewise.ai/threats/cve-2025-53521-f5-big-ip-stack-based-buffer-overflow-in-apm  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2025-10-15. Updated: 2026-05-15  
License: CC BY 4.0 with a link back

CVE-2025-53521 · Severity: critical · CVSS 9.8 · Exploited in the wild · Published 2025-10-15

F5 BIG-IP Access Policy Manager (APM), a solution used to manage secure remote access to corporate applications, contains a critical security flaw. An unauthenticated attacker can exploit this vulnerability by sending malicious network traffic to a virtual server, potentially taking full control of the system. This vulnerability is known to be actively exploited in the wild, posing a significant risk to organizational data and network integrity.

Technologies: [F5 BIG-IP](https://junglewise.ai/threats/technologies/big-ip), [F5 Big-Ip Access Policy Manager](https://junglewise.ai/threats/technologies/big-ip-access-policy-manager). Vendors: [F5](https://junglewise.ai/threats/vendors/f5).

## Quick answers

**Is CVE-2025-53521 exploited in the wild?** Yes. CVE-2025-53521 is known to be exploited in the wild, first recorded on 27 March 2026. Treat it as urgent.

**How severe is CVE-2025-53521?** Critical severity, with a CVSS score of 9.8, published 15 October 2025.

**Which products and versions are affected?** F5 Big-Ip Access Policy Manager 15.1.0 to 15.1.10.7, 16.1.0 to 16.1.6.0, 17.1.0 to 17.1.2, 17.5.0 to 17.5.1.2.

**Is there a fix for CVE-2025-53521?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2025-53521 attacked?** It is attacked over the network, in a network appliance.

**Am I affected by CVE-2025-53521?** Check whether you run F5 BIG-IP or F5 Big-Ip Access Policy Manager at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A stack-based buffer overflow (CWE-121) exists in F5 BIG-IP when an Access Policy Manager (APM) policy is configured on a virtual server. The vulnerability is triggered by processing specific malicious network traffic, allowing an unauthenticated remote attacker to execute arbitrary code with high privileges. This flaw has been observed in active exploitation. Patches are available in versions 15.1.10.8, 16.1.6.1, 17.1.3, and 17.5.1.3; users are advised to update immediately or apply vendor-recommended mitigations.

## Affected products

- F5 BIG-IP Access Policy Manager (APM) 15.1.0 to 15.1.10.7, 16.1.0 to 16.1.6.0, 17.1.0 to 17.1.2, 17.5.0 to 17.5.1.2

## Timeline

- 2026-03-27: advisory: Initial publication and CISA KEV addition
- 2026-03-27: exploited: Confirmed active exploitation in the wild

## Related threats

- [F5 BIG-IP privilege escalation in TMUI](https://junglewise.ai/threats/cve-2026-66842-f5-big-ip-privilege-escalation-in-tmui)
- [F5 BIG-IP Configuration utility error message spoofing](https://junglewise.ai/threats/cve-2026-63020-f5-big-ip-configuration-utility-error-message-spoofing)
- [F5 BIG-IP denial of service in HTTP/2 profile memory management](https://junglewise.ai/threats/cve-2026-59762-f5-big-ip-denial-of-service-in-http-2-profile-memory-management)
- [F5 BIG-IP and BIG-IQ incorrect permission assignment in tmsh and iControl REST](https://junglewise.ai/threats/cve-2026-42937-f5-big-ip-and-big-iq-incorrect-permission-assignment-in-tmsh-and)
- [F5 BIG-IP Appliance mode restriction bypass via path traversal](https://junglewise.ai/threats/cve-2026-42930-f5-big-ip-appliance-mode-restriction-bypass-via-path-traversal)