CVE-2025-20133
📋 TL;DR
An unauthenticated remote attacker can cause Cisco Secure Firewall ASA and FTD devices to stop responding to Remote Access SSL VPN authentication requests by sending a crafted request, resulting in a denial-of-service condition. This affects organizations using these devices for VPN access.
💻 Affected Systems
- Cisco Secure Firewall ASA Software
- Cisco Secure Firewall FTD Software
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
Complete VPN service disruption preventing all remote access, requiring device reboot to restore functionality.
Likely Case
Temporary VPN service outage affecting remote users until traffic subsides or device recovers.
If Mitigated
Minimal impact with proper network segmentation and monitoring allowing quick detection and response.
🎯 Exploit Status
Crafting malicious authentication request requires understanding of protocol but no authentication needed
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Cisco advisory for specific fixed versions
Vendor Advisory: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-vpn-dos-mfPekA6e
Restart Required: Yes
Instructions:
1. Review Cisco advisory for affected versions 2. Download appropriate fixed software version 3. Apply patch during maintenance window 4. Verify VPN functionality post-update
🔧 Temporary Workarounds
Disable Remote Access SSL VPN
allTemporarily disable the vulnerable feature if not essential
no webvpn
no enable outside
Restrict VPN Access
allLimit VPN access to trusted IP ranges using ACLs
access-list VPN-ACL permit ip trusted-net any
access-group VPN-ACL in interface outside
🧯 If You Can't Patch
- Implement network segmentation to isolate VPN traffic
- Deploy intrusion prevention system with DoS protection rules
🔍 How to Verify
Check if Vulnerable:
Check device version against affected versions in Cisco advisoryCheck Version:
show version | include VersionVerify Fix Applied:
Verify installed version matches fixed version from advisory and test VPN connectivity📡 Detection & Monitoring
Log Indicators:
- Multiple authentication failures
- VPN service restart events
- High CPU/memory usage on VPN process
Network Indicators:
- Unusual spike in VPN authentication requests
- VPN service unresponsive to legitimate requests
SIEM Query:
source="cisco-asa" AND (event_id=722051 OR event_id=722041) AND message="Authentication failed" count>10 per 60s