CVE-2021-1621: Cisco IOS XE

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 XE Software could allow an unauthenticated, adjacent attacker to cause a queue wedge on an interface that receives specific Layer 2 frames, resulting in a denial of service (DoS) condition. This vulnerability is due to improper handling of certain Layer 2 frames. An attacker could exploit this vulnerability by sending specific Layer 2 frames on the segment the router is connected to. A successful exploit could allow the attacker to cause a queue wedge on the interface, resulting in a DoS condition.

Affected products

• Cisco IOS XE: before 17.3.1 (fixed in 17.3.1)

Published 2021-09-23. Last modified 2026-06-17.