CVE-2021-34699: Cisco IOS and IOS XE Software TrustSec CLI Parser Denial of Service Vulnerability

Severity: high (CVSS 7.7 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.2% 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-435

Description

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: 12.2(6)i1, 15.0(1)sy, 15.0(1)sy1, 15.0(1)sy2, 15.0(1)sy3, 15.0(1)sy4 (+509)
Cisco IOS XE: 3.3.0se, 3.3.0xo, 3.3.1se, 3.3.1xo, 3.3.2se, 3.3.2xo (+313)

References

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