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CVE-2025-53521

Critical 9.8 Exploited in the wild (KEV)

Confirmed active exploitation — CISA KEV catalog

Name
F5 BIG-IP Stack-Based Buffer Overflow Vulnerability
Added to catalog
Remediation due date (US federal)
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.

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.

Metrics

CVSS 3.1
9.8 (CRITICAL) Score source: CNA CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CVSS 4.0
9.3 (CRITICAL) Score source: CNA CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
EPSS — exploit probability
2% (percentile: 83) as of 1 November 2026
CWE
CWE-121

Affected products

f5: big-ip access policy manager

References