CVE-2025-20145
📋 TL;DR
This vulnerability allows unauthenticated remote attackers to bypass egress ACLs on Cisco IOS XR devices when traffic flows between different line cards. Network administrators using affected Cisco IOS XR Software versions are impacted. The bypass could allow unauthorized traffic to pass through network boundaries.
💻 Affected Systems
- Cisco IOS XR Software
📦 What is this software?
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⚠️ Risk & Real-World Impact
Worst Case
Attackers could exfiltrate sensitive data, establish command and control channels, or pivot to internal networks by bypassing critical egress filtering.
Likely Case
Attackers could bypass security policies to send unauthorized traffic out of protected networks, potentially enabling data exfiltration or external communications.
If Mitigated
With proper network segmentation and defense-in-depth, the impact would be limited to specific network segments rather than entire environments.
🎯 Exploit Status
Exploitation requires sending traffic through affected device; 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-modular-ACL-u5MEPXMm
Restart Required: Yes
Instructions:
1. Review Cisco advisory for affected versions. 2. Download appropriate fixed software version. 3. Schedule maintenance window. 4. Backup configuration. 5. Install update following Cisco IOS XR upgrade procedures. 6. Verify ACL functionality post-upgrade.
🧯 If You Can't Patch
- Implement additional network segmentation to limit traffic flow between line cards
- Deploy inline security controls (firewalls/IPS) to monitor and block suspicious egress traffic
🔍 How to Verify
Check if Vulnerable:
Check Cisco IOS XR version against affected versions in Cisco advisory; verify if egress ACLs are configured on interfaces spanning different line cardsCheck Version:
show version | include Cisco IOS XRVerify Fix Applied:
Verify installed version matches fixed version from Cisco advisory; test ACL functionality with traffic crossing between line cards📡 Detection & Monitoring
Log Indicators:
- Unexpected traffic patterns bypassing ACLs
- ACL permit/deny counters showing anomalies
Network Indicators:
- Traffic that should be blocked by egress ACLs reaching external networks
- Unusual outbound connections from protected segments
SIEM Query:
Search for network traffic events where source/destination pairs match ACL deny rules but traffic appears to flow successfully