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A vulnerability in the Layer 3 multicast feature of Cisco IOS XR Software for Cisco ASR 9000 Series Aggregation Services Routers, ASR 9902 Compact High-Performance Routers, and ASR 9903 Compact High-Performance Routers could allow an unauthenticated, remote attacker to cause a line card to reset, resulting in a denial of service (DoS) condition. This vulnerability is due to the incorrect handling of malformed IPv4 multicast packets that are received on line cards where the interface has either an IPv4 access control list (ACL) or a QoS policy applied. An attacker could exploit this vulnerability by sending crafted IPv4 multicast packets through an affected device. A successful exploit could allow the attacker to cause line card exceptions or a hard reset. Traffic over that line card would be lost while the line card reloads.
Use CWE-20, Cisco vendor hub and Ios Xr product page to widen CVE-2025-20146 into its surrounding weakness, vendor, and product context.
Compare it with CVE-2025-20363, CVE-2025-20138 and CVE-2025-20154 for nearby disclosures in the same product family. Additional editorial context is available in The Weekly Cybersecurity Brief: January 30th, 2026.