Exploited CVEs / F5 / CVE-2025-53521
CVE-2025-53521
F5 BIG-IP Stack-Based Buffer Overflow Vulnerability. Exploitation in the wild is confirmed by CISA, not predicted. Federal agencies were required to remediate by 2026-03-30 (that deadline has passed); treat that date as the outer bound for your own environment. Check the vendor security advisory for the fix.
Risk summary
Actively exploited F5 BIG-IP vulnerability, Critical severity, CVSS 9.8. Added to the CISA KEV catalog 2026-03-27.
Senserva AI Opinion for CVE-2025-53521
A stack-based buffer overflow in F5 BIG-IP APM offers remote code execution on the appliance that terminates your VPN and application access sessions, rated Critical at CVSS 9.8 and confirmed exploited since 2026-03-27. BIG-IP devices sit in front of critical applications and hold session and credential material in memory. The APM module scoping means access-policy deployments are the exposed subset of the BIG-IP fleet.
Do this: Update BIG-IP systems running APM first and confirm their management interfaces are not internet-reachable.
AI-generated from public data, 2026-07-07. Verify against the vendor advisory before acting.
Senserva AI Opinion and rich prompt for CVE-2025-53521
Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.
Updated August 14, 2026. Data refreshed on every build from MSRC, CISA KEV, and FIRST EPSS.
Full tracking and change history for CVE-2025-53521
- Published
- 2026-03-27
- Last revised
- 2026-03-27
- Changes tracked
- 1
Published and last-revised dates are authoritative, from Microsoft MSRC (or the CISA KEV date-added). Senserva additionally records day-to-day changes from 2026-07-07, refreshed several times a day; the change count reflects that forward-only tracking.
- 2026-03-27 added to the CISA KEV catalog by CISA
- 2026-07-17 CVSS 0.0 to 9.8; EPSS first scored at 2.2%
Recorded by Senserva on the dates shown, from CISA KEV and FIRST EPSS. This is what moved and when, which neither the vendor advisory nor NVD publishes.
CISA required action
Federal (BOD 22-01) remediation due date: 2026-03-30 (past due).
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
Official fix for CVE-2025-53521
Check the vendor's security advisory channel for the patched BIG-IP versions and workarounds.
Common questions about CVE-2025-53521
Is CVE-2025-53521 actively exploited?
Yes. CVE-2025-53521 was added to the CISA Known Exploited Vulnerabilities (KEV) catalog on 2026-03-27, which means exploitation in the wild has been confirmed, not predicted. Its EPSS 30-day exploitation probability is 2.2%.
What is the CISA deadline and required action for CVE-2025-53521?
CISA set the federal (BOD 22-01) remediation due date at 2026-03-30, which has passed; treat any unremediated system as overdue. The verbatim 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.
What fixes CVE-2025-53521?
Check the vendor's security advisory for the patched BIG-IP versions and any workarounds. KEV listing makes this a fix-first item: patch it ahead of higher-CVSS issues nobody is exploiting.
Can I ask my own AI about CVE-2025-53521?
Yes. This page includes a free, ready-to-paste AI prompt containing CVE-2025-53521's key facts: severity, CVSS, EPSS, the KEV date, the CISA due date, and the required action. Copy it into Claude, ChatGPT, or Copilot; the data is refreshed twice a day (5 AM and 3 PM US Central).
Scope and sources
- More exploited F5 CVEs
All F5 exploited CVEs on one page: F5 vulnerabilities actively exploited.
- Authoritative references
Every actively exploited CVE, searchable with due dates and CSV export: the exploited-CVE tracker. The newest additions: exploited this week.