CISCO Security Advisory
Published Date: Not specified
CVE: CVE-2026-76505
Advisory Summary
🎯 ⚠️ Cisco IOS XR DoS Advisory for ASR 9000/9900 Series (IPv4 Unicast Processing)
🚨 ALARMS (Security Impact: High | CVE-2026-76505)
Cisco reports a high-severity Denial of Service (DoS) vulnerability in Cisco IOS XR Software affecting ASR 9000 and ASR 9900 Series Aggregation Services Routers, including ASR 9902 and ASR 9903 compact high-performance routers.
- Line card reset or shutdown
- Traffic loss while the line card recovers
- Potential persistent NP shutdown state under repeated triggering, requiring an explicit line card reload to restore traffic
- The flaw is in the IPv4 packet-processing path
- Crafted packets are received on an affected line card interface and incorrectly processed as for-us traffic
- Transit IPv4 traffic does not trigger the issue
- IPv6 traffic cannot trigger the vulnerability
- ✅ Cisco has released software updates to address the issue
- ❌ No workarounds are available
🧠 Actionable Guidance for Market Professionals
1. Verify device exposure: Identify affected platforms/line cards running vulnerable IOS XR versions (ASR 9000/9900 + ASR 9902/9903).
2. Plan controlled upgrades: Apply the official Cisco IOS XR fix via your change management window, prioritizing high-availability sites and edge/aggregation roles.
3. Hunt & reduce risk: Since the issue is triggered by crafted IPv4 packets to interfaces, review whether you can detect abnormal IPv4 unicast patterns at the edge/PE/aggregation layer (ACL/RTBH controls, sFlow/NetFlow telemetry, IDS/IPS coverage).
4. Prepare for impact: In environments where DoS could cause routing/adjacency instability, ensure operational runbooks cover line card reload procedures.
🔐 Vulnerability Name (for tracking): CVE-2026-76505
📌 Scope notes: IPv4 only; transit IPv4 not affected; IPv6 not affected.
Reference: Vendor Advisory