CVE-2023-20049
📋 TL;DR
An unauthenticated remote attacker can send crafted IPv4 BFD packets to cause line card resets on affected Cisco routers, resulting in denial of service. This affects Cisco ASR 9000, ASR 9902, and ASR 9903 routers running IOS XR Software with BFD hardware offload enabled.
💻 Affected Systems
- Cisco ASR 9000 Series Aggregation Services Routers
- Cisco ASR 9902 Compact High-Performance Routers
- Cisco ASR 9903 Compact High-Performance Routers
📦 What is this software?
Ios Xr by Cisco
Ios Xr by Cisco
Ios Xr by Cisco
⚠️ Risk & Real-World Impact
Worst Case
Multiple line cards reset simultaneously, causing widespread network outages and traffic loss across the affected router
Likely Case
Individual line card resets causing localized DoS for traffic passing through that specific card
If Mitigated
No impact if BFD hardware offload is disabled or devices are patched
🎯 Exploit Status
Exploitation requires sending malformed BFD packets to vulnerable devices
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Refer to Cisco Security Advisory for specific fixed releases
Vendor Advisory: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-bfd-XmRescbT
Restart Required: Yes
Instructions:
1. Review Cisco Security Advisory for fixed releases. 2. Upgrade IOS XR Software to recommended version. 3. Reload affected line cards after upgrade.
🔧 Temporary Workarounds
Disable BFD Hardware Offload
cisco-ios-xrDisable the BFD hardware offload feature on vulnerable line cards
configure
bfd
no hw-offload
🧯 If You Can't Patch
- Disable BFD hardware offload on all vulnerable line cards
- Implement network segmentation to restrict BFD traffic to trusted sources
🔍 How to Verify
Check if Vulnerable:
Check if BFD hardware offload is enabled: 'show bfd hw-offload' and verify IOS XR version against advisoryCheck Version:
show versionVerify Fix Applied:
Verify IOS XR version is at or above fixed release and BFD hardware offload status📡 Detection & Monitoring
Log Indicators:
- Line card reset messages
- BFD protocol errors
- Hardware exception logs
Network Indicators:
- Unexpected BFD packet floods
- Line card interface flapping
SIEM Query:
source="cisco-router" AND ("line card reset" OR "BFD error" OR "hardware exception")