CVE-2021-34699: Cisco IOS

High severity, CVSS 7.7. EPSS: 1.2% chance of exploitation in the next 30 days.

A vulnerability in the TrustSec CLI parser of Cisco IOS and Cisco IOS XE Software could allow an authenticated, remote attacker to cause an affected device to reload. This vulnerability is due to an improper interaction between the web UI and the CLI parser. An attacker could exploit this vulnerability by requesting a particular CLI command to be run through the web UI. A successful exploit could allow the attacker to cause the device to reload, resulting in a denial of service (DoS) condition.

Affected products

• Cisco IOS: version 12.2(6)i1 only; version 15.0(1)sy only; version 15.0(1)sy1 only; version 15.0(1)sy2 only; version 15.0(1)sy3 only; version 15.0(1)sy4 only; …
• Cisco IOS XE: version 3.3.0se only; version 3.3.0xo only; version 3.3.1se only; version 3.3.1xo only; version 3.3.2se only; version 3.3.2xo only; …

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