Threats / F5 / CVE-2025-53521
CVE-2025-53521
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-06-22
F5 BIG-IP vulnerability
F5 BIG-IP APM contains a stack-based buffer overflow vulnerability enabling remote code execution. The flaw is actively exploited in the wild.
Verdict
Today item — known-exploited.
A remotely exploitable stack buffer overflow in F5 BIG-IP APM permits unauthenticated attackers to execute arbitrary code with system privileges. Active exploitation confirms operational risk despite low EPSS probability.
01
Is it exploitable?
— the evidence, ranked above the scoreReported exploitation
7 independent public reports of in-the-wild exploitation are cataloged.Distinct reporting sources (vendor, incident response, government); open them for the underlying claims.
Exploited in the wild
Listed in the CISA Known Exploited Vulnerabilities catalog (added 2026-03-27).
Probability (EPSS)
EPSS 0.02246 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
Affected: F5, BIG-IP. Confirm exact fixed builds in the vendor advisory.
Weakness (CWE)
Mapped to CWE-121 Stack-based Buffer Overflow — weakness family: Memory safety.CWE assignment from the public NVD record; the weakness class drives how the flaw is exploited.
02
Who’s exploiting it?
— attribution turns risk into urgencyAttribution not established
No confirmed (advisory-backed) threat-actor attribution is established for this record. Absence of a named actor is not absence of compromise — see Coverage & confidence.
03
Why it matters
— the attack path, told twice: adversary, then board1
Front door — unauthenticated access narrative 1
Attacker
I craft a malicious input that overflows the stack buffer in BIG-IP APM to overwrite return addresses and inject shellcode.
Business
Attackers gain code execution on critical load balancing infrastructure, enabling lateral movement into protected networks and data exfiltration.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
I execute arbitrary commands with the privileges of the BIG-IP process to establish persistence and maintain access.
Business
Compromised BIG-IP instances become persistent footholds for ongoing reconnaissance and attacks against downstream systems.
3
Lateral reach — past segmentation narrative 3
Attacker
I pivot from the compromised BIG-IP to intercept, modify, or redirect traffic flowing through the load balancer.
Business
Business continuity is disrupted; customer data and transactions passing through BIG-IP are exposed to interception and manipulation.
04
What to do
— defensible action- Remediate per the vendor advisory — confirm the fixed build for your version and verify exposure.1
Say it to the boardA vulnerability with this evidence profile is a defensible budget line, not a backlog ticket — fund the change against the proof above.
05