CVE-2025-53521

F5 BIG-IP: Stack-Based Buffer Overflow

As of , CVE-2025-53521 in F5 BIG-IP is on CISA's list of exploited vulnerabilities: CISA listed it on . Our patch-first group: Patch soon.

Exploited
Yes: CISA listed it on 27 March 2026
US federal deadline
30 March 20263 days after CISA listed it. US federal civilian agencies must fix it by then.
Used in ransomware campaigns
Not known to CISA
EPSS score
0.02Higher than 82% of the CVEs EPSS scores. EPSS estimates the chance of exploitation activity in the next 30 days.
Public exploit
None foundNeither Metasploit nor Exploit-DB lists one.
Fix
Vendor advice: my.f5.comLinks below, from CISA's entry.

What CISA says to do

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

CISA's required action

  • my.f5.comPlease adhere to F5’s guidelines to assess exposure and mitigate risks. Check for signs of potential compromise on all internet accessible…
  • my.f5.com
  • my.f5.com

What the flaw is

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

CISA's 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.

The CVE record's description, from f5

CVE published
15 October 2025
Assigned by
f5
CVSS
9.3 Critical (CVSS 4.0, from the CNA)
CWE-121
Stack-based Buffer Overflow
CISA SSVC, exploitation
active
CISA SSVC, automatable
yes
CISA SSVC, technical impact
total

Timeline

  1. The CVE record was published.
  2. CISA added it to its list of exploited vulnerabilities.
  3. CISA changed its entry. Edited: description.
  4. The US federal deadline to fix it.
  5. CISA changed its entry. Edited: weakness list, description and name.

BIG-IP: other exploited entries

VulnerabilityProductOur groupListedDeadlineEPSS
CVE-2022-1388Missing AuthenticationF5 BIG-IPPatch this weekRansomware use; Metasploit module; EPSS 0.990.99
CVE-2020-5902Traffic Management User Interface (TMUI) Remote Code ExecutionF5 BIG-IPPatch this weekRansomware use; Metasploit module; EPSS 0.990.99

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