IRONSMITHINTEL
CRITICALCVSS9.8
|
Actively Exploited
|CISA KEV|CVE-2025-53521|Auth: none — unauthenticated|Reboot: required|Manual only

F5 BIG-IP Stack-Based Buffer Overflow Vulnerability

F5 BIG-IP APM contains a stack-based buffer overflow vulnerability that could allow a threat actor to achieve remote code execution.

Published Oct 15, 2025 · Updated May 16, 2026
Why patchRisk explained in plain English
Worst-case scenarioIf unpatched

A remote attacker, without authentication, can achieve full data confidentiality loss, arbitrary modification of data, complete denial of service or system unavailability. Federal agencies are required to remediate by 2026-03-30 under CISA BOD 22-01.

How the attack worksNo clicks needed

This is a Stack-based Buffer Overflow (CWE-121) vulnerability in F5 BIG-IP. 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. Exploitation requires remote network access, low attack complexity, no authentication required, and no user interaction required.

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Phishing link

🖼

Malicious file

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Server compromised

Am I affected?Quick check

Probably yes if any of these apply:

IT Security
Running big-ip access policy manager: 15.1.0 ≤ v < 15.1.10.8, 16.1.0 ≤ v < 16.1.6.1, 17.1.0 ≤ v < 17.1.3, 17.5.0 ≤ v < 17.5.1.3
Real-world incidentsWhat we've seen

CISA added this CVE to the Known Exploited Vulnerabilities catalog on 2026-03-27 based on evidence of active exploitation in the wild. Federal agencies required to remediate by 2026-03-30.

How to patch

Manual remediation steps

Apply the Vendor Patch

This vulnerability is in the CISA Known Exploited Vulnerabilities catalog — apply the vendor's security update as soon as possible.

CISA required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

References

    1
    Vendor advisory: https://my.f5.com/manage/s/article/K000160486
    1
    NVD entry: https://nvd.nist.gov/vuln/detail/CVE-2025-53521
    1
    CISA KEV: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-53521
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