CVE-2021-34713: Cisco IOS XR

High severity, CVSS 7.4. EPSS: 0.4% chance of exploitation in the next 30 days.

A vulnerability in the Layer 2 punt code of Cisco IOS XR Software running on Cisco ASR 9000 Series Aggregation Services Routers could allow an unauthenticated, adjacent attacker to cause the affected line card to reboot. This vulnerability is due to incorrect handling of specific Ethernet frames that cause a spin loop that can make the network processors unresponsive. An attacker could exploit this vulnerability by sending specific types of Ethernet frames on the segment where the affected line cards are attached. A successful exploit could allow the attacker to cause the affected line card to reboot.

Affected products

• Cisco IOS XR: from 6.4, before 6.6.3 (fixed in 6.6.3); from 6.7, before 6.7.1 (fixed in 6.7.1); from 7.0, before 7.0.2 (fixed in 7.0.2); from 7.1, before 7.1.1 (fixed in 7.1.1)

Published 2021-09-09. Last modified 2026-06-17.