CVE-2025-20219
📋 TL;DR
This vulnerability allows unauthenticated remote attackers to bypass access control rules on Cisco ASA/FTD firewalls by sending traffic to loopback interfaces that should have been blocked. It affects organizations using Cisco Secure Firewall ASA Software and Cisco Secure Firewall Threat Defense Software with vulnerable configurations.
💻 Affected Systems
- Cisco Secure Firewall Adaptive Security Appliance (ASA) Software
- Cisco Secure Firewall Threat Defense (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
Attackers could bypass critical security controls, potentially accessing restricted internal networks or services through the firewall's loopback interface.
Likely Case
Limited information exposure or unauthorized access to services configured on loopback interfaces, but constrained by existing network segmentation.
If Mitigated
Minimal impact if loopback interfaces have no sensitive services or are protected by additional security layers.
🎯 Exploit Status
Exploitation requires knowledge of loopback interface configurations and targeting specific traffic patterns.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Refer to Cisco Security Advisory for fixed versions
Vendor Advisory: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asa-ftd-acl-bypass-mtPze9Yh
Restart Required: No
Instructions:
1. Review Cisco Security Advisory for affected versions. 2. Upgrade to recommended fixed release. 3. Apply configuration changes if specified in advisory.
🔧 Temporary Workarounds
Restrict Loopback Interface Access
allApply additional access control rules or remove unnecessary rules from loopback interfaces
access-list LOOPBACK-ACL extended deny ip any any
access-group LOOPBACK-ACL in interface loopbackX
🧯 If You Can't Patch
- Implement network segmentation to isolate loopback interfaces from untrusted networks
- Deploy intrusion prevention systems to detect and block exploitation attempts
🔍 How to Verify
Check if Vulnerable:
Check Cisco ASA/FTD version against affected versions listed in Cisco Security AdvisoryCheck Version:
show version | include VersionVerify Fix Applied:
Verify upgraded to fixed version and test loopback interface ACL enforcement📡 Detection & Monitoring
Log Indicators:
- Unexpected traffic to loopback interfaces
- ACL bypass events in firewall logs
Network Indicators:
- Traffic patterns targeting loopback IP addresses that should be blocked
SIEM Query:
firewall_event:bypass AND interface:loopback*