CVE-2021-1621: Cisco IOS XE Software Interface Queue Wedge Denial of Service Vulnerability

Severity: high (CVSS 7.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-09-23 · updated 2026-06-17
Weakness: CWE-399

Description

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

How to fix

Upgrade to a fixed version: Cisco IOS XE 17.3.1. Check the vendor advisory for mitigations.

References

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