CVE-2025-53521 F5 BIG-IP: memory-safety flaw
In plain words: The program mishandles the memory it uses to keep track of data. A specially made input can scramble that memory. Usually lets an attacker crash the program or run their own code with its permissions.
Confirmed exploited by CISA on · US federal patch deadline Mar 30, 2026
What to do
- Install F5's security update for BIG-IP. If no update exists, follow the vendor's workaround or stop using the product until one ships.
- Patch edge devices first — attackers often start scanning for them within hours of a fix.
- Never expose the device's admin page to the internet.
- After patching a device that was exposed, follow the vendor's compromise checks, end active sessions and change passwords.
Who is affected
Work IT. Aimed mostly at company systems — you are affected through the companies you use, not your own phone.
What's at risk: They face the internet and guard the whole network, so a flaw here can hand attackers a way in — and these devices usually run no antivirus, so break-ins go unnoticed.
The details
- Official name
- F5 BIG-IP Stack-Based Buffer Overflow Vulnerability
- Product
- F5 BIG-IP
- CISA description
- F5 BIG-IP APM contains a stack-based buffer overflow vulnerability that could allow a threat actor to achieve remote code execution.
- Type of flaw
- Memory-safety flaw (CWE-121)
- Confirmed exploited
- Mar 27, 2026
- US federal patch deadline
- Mar 30, 2026
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Answering about CVE-2025-53521 ·
Questions about CVE-2025-53521
Is CVE-2025-53521 being exploited?
Yes. CISA added CVE-2025-53521 to its Known Exploited Vulnerabilities catalog on Mar 27, 2026, which means there is reliable evidence of real-world attacks.
How do I fix CVE-2025-53521?
Install F5's security update for BIG-IP. If no update exists, follow the vendor's workaround or stop using the product until one ships. Patch edge devices first — attackers often start scanning for them within hours of a fix.
Am I affected by CVE-2025-53521?
Only if you use F5 BIG-IP. Aimed mostly at company systems — you are affected through the companies you use, not your own phone.