Exploited vulnerability · CISA KEV

Is CVE-2025-53521 exploited? Yes: in CISA KEV since 27 Mar 2026

Gociux · F5 BIG-IP · data: CISA KEV, CVE record, FIRST EPSS

Yes. CVE-2025-53521, F5 BIG-IP Stack-Based Buffer Overflow Vulnerability, is being exploited in the wild. CISA added it to its Known Exploited Vulnerabilities catalog on 27 Mar 2026, 163 days after it was published. It affects F5 BIG-IP, an internet-facing product of the kind attackers use for initial access. If you run it, CISA's required action is: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

What it is

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

What to do

1. Check whether you run it. Look for BIG-IP in your asset inventory, including appliances and cloud images. Stack check lists every exploited F5 CVE at once.
2. Apply the fix. Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
3. If you can't patch today, take the affected service off the internet or restrict who can reach it, and check its logs for signs of compromise since 15 Oct 2025.
4. Get told next time. Email alerts when CISA adds a CVE for F5.

Other exploited CVEs in BIG-IP

• CVE-2022-1388: F5 BIG-IP Missing Authentication Vulnerability (10 May 2022)
• CVE-2020-5902: F5 BIG-IP Traffic Management User Interface (TMUI) Remote Code Execution Vulnerability (3 Nov 2021)

References

• my.f5.com/manage/s/article/K000160486
• my.f5.com/manage/s/article/K11438344
• nvd.nist.gov/vuln/detail/CVE-2025-53521

Sources: CISA KEV (exploitation, ransomware use, required action, due date), the CVE record (publication date, CVSS, CNA), NVD and FIRST EPSS (live score). More: all KEV additions in March 2026 · F5 scorecard · act-now radar.