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

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.

Published: 2021-09-23 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-34699 is rated Moderate Risk (53.2/100): CVSS High severity, with medium exploitation likelihood (EPSS 1.15%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-34699

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.70% 1.15% +0.45%
2 2025-12-28 0.79% 0.70% -0.08%
3 2025-12-27 — 0.79% —

Full EPSS history (16 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-34699

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.7 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.1 4.0 [email protected]
7.7 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.1 4.0 [email protected]
6.8 2.0 MEDIUM
AV:N/AC:L/Au:S/C:N/I:N/A:C Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:S)
A single authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:C)
Complete availability impact.
 8.0 6.9 [email protected]

Weakness enumeration for CVE-2021-34699

Affected software / configurations for CVE-2021-34699

Vendor Product Version Raw CPE
cisco ios 12.2\(6\)i1 cpe:2.3:o:cisco:ios:12.2\(6\)i1:*:*:*:*:*:*:*
cisco ios 15.0\(1\)sy cpe:2.3:o:cisco:ios:15.0\(1\)sy:*:*:*:*:*:*:*
cisco ios 15.0\(1\)sy1 cpe:2.3:o:cisco:ios:15.0\(1\)sy1:*:*:*:*:*:*:*
cisco ios 15.0\(1\)sy2 cpe:2.3:o:cisco:ios:15.0\(1\)sy2:*:*:*:*:*:*:*
cisco ios 15.0\(1\)sy3 cpe:2.3:o:cisco:ios:15.0\(1\)sy3:*:*:*:*:*:*:*
cisco ios 15.0\(1\)sy4 cpe:2.3:o:cisco:ios:15.0\(1\)sy4:*:*:*:*:*:*:*
cisco ios 15.0\(1\)sy5 cpe:2.3:o:cisco:ios:15.0\(1\)sy5:*:*:*:*:*:*:*
cisco ios 15.0\(1\)sy6 cpe:2.3:o:cisco:ios:15.0\(1\)sy6:*:*:*:*:*:*:*
cisco ios 15.0\(1\)sy7 cpe:2.3:o:cisco:ios:15.0\(1\)sy7:*:*:*:*:*:*:*
cisco ios 15.0\(1\)sy7a cpe:2.3:o:cisco:ios:15.0\(1\)sy7a:*:*:*:*:*:*:*
cisco ios 15.0\(1\)sy8 cpe:2.3:o:cisco:ios:15.0\(1\)sy8:*:*:*:*:*:*:*
cisco ios 15.0\(1\)sy9 cpe:2.3:o:cisco:ios:15.0\(1\)sy9:*:*:*:*:*:*:*
cisco ios 15.0\(1\)sy10 cpe:2.3:o:cisco:ios:15.0\(1\)sy10:*:*:*:*:*:*:*
cisco ios 15.0\(2\)ej cpe:2.3:o:cisco:ios:15.0\(2\)ej:*:*:*:*:*:*:*
cisco ios 15.0\(2\)ej1 cpe:2.3:o:cisco:ios:15.0\(2\)ej1:*:*:*:*:*:*:*
cisco ios 15.0\(2\)ek cpe:2.3:o:cisco:ios:15.0\(2\)ek:*:*:*:*:*:*:*
cisco ios 15.0\(2\)ek1 cpe:2.3:o:cisco:ios:15.0\(2\)ek1:*:*:*:*:*:*:*
cisco ios 15.0\(2\)ex cpe:2.3:o:cisco:ios:15.0\(2\)ex:*:*:*:*:*:*:*
cisco ios 15.0\(2\)ex1 cpe:2.3:o:cisco:ios:15.0\(2\)ex1:*:*:*:*:*:*:*
cisco ios 15.0\(2\)ex2 cpe:2.3:o:cisco:ios:15.0\(2\)ex2:*:*:*:*:*:*:*
cisco ios 15.0\(2\)ex3 cpe:2.3:o:cisco:ios:15.0\(2\)ex3:*:*:*:*:*:*:*
cisco ios 15.0\(2\)ex4 cpe:2.3:o:cisco:ios:15.0\(2\)ex4:*:*:*:*:*:*:*
cisco ios 15.0\(2\)ex5 cpe:2.3:o:cisco:ios:15.0\(2\)ex5:*:*:*:*:*:*:*
cisco ios 15.0\(2\)ex6 cpe:2.3:o:cisco:ios:15.0\(2\)ex6:*:*:*:*:*:*:*
cisco ios 15.0\(2\)ex7 cpe:2.3:o:cisco:ios:15.0\(2\)ex7:*:*:*:*:*:*:*
cisco ios 15.0\(2\)ex8 cpe:2.3:o:cisco:ios:15.0\(2\)ex8:*:*:*:*:*:*:*
cisco ios 15.0\(2\)ex10 cpe:2.3:o:cisco:ios:15.0\(2\)ex10:*:*:*:*:*:*:*
cisco ios 15.0\(2\)ex11 cpe:2.3:o:cisco:ios:15.0\(2\)ex11:*:*:*:*:*:*:*
cisco ios 15.0\(2\)ex12 cpe:2.3:o:cisco:ios:15.0\(2\)ex12:*:*:*:*:*:*:*
cisco ios 15.0\(2\)ex13 cpe:2.3:o:cisco:ios:15.0\(2\)ex13:*:*:*:*:*:*:*
cisco ios 15.0\(2\)ey cpe:2.3:o:cisco:ios:15.0\(2\)ey:*:*:*:*:*:*:*
cisco ios 15.0\(2\)ey1 cpe:2.3:o:cisco:ios:15.0\(2\)ey1:*:*:*:*:*:*:*
cisco ios 15.0\(2\)ey2 cpe:2.3:o:cisco:ios:15.0\(2\)ey2:*:*:*:*:*:*:*
cisco ios 15.0\(2\)ey3 cpe:2.3:o:cisco:ios:15.0\(2\)ey3:*:*:*:*:*:*:*
cisco ios 15.0\(2\)ez cpe:2.3:o:cisco:ios:15.0\(2\)ez:*:*:*:*:*:*:*
cisco ios 15.0\(2\)se cpe:2.3:o:cisco:ios:15.0\(2\)se:*:*:*:*:*:*:*
cisco ios 15.0\(2\)se1 cpe:2.3:o:cisco:ios:15.0\(2\)se1:*:*:*:*:*:*:*
cisco ios 15.0\(2\)se2 cpe:2.3:o:cisco:ios:15.0\(2\)se2:*:*:*:*:*:*:*
cisco ios 15.0\(2\)se3 cpe:2.3:o:cisco:ios:15.0\(2\)se3:*:*:*:*:*:*:*
cisco ios 15.0\(2\)se4 cpe:2.3:o:cisco:ios:15.0\(2\)se4:*:*:*:*:*:*:*
cisco ios 15.0\(2\)se5 cpe:2.3:o:cisco:ios:15.0\(2\)se5:*:*:*:*:*:*:*
cisco ios 15.0\(2\)se6 cpe:2.3:o:cisco:ios:15.0\(2\)se6:*:*:*:*:*:*:*
cisco ios 15.0\(2\)se7 cpe:2.3:o:cisco:ios:15.0\(2\)se7:*:*:*:*:*:*:*
cisco ios 15.0\(2\)se8 cpe:2.3:o:cisco:ios:15.0\(2\)se8:*:*:*:*:*:*:*
cisco ios 15.0\(2\)se9 cpe:2.3:o:cisco:ios:15.0\(2\)se9:*:*:*:*:*:*:*
cisco ios 15.0\(2\)se10 cpe:2.3:o:cisco:ios:15.0\(2\)se10:*:*:*:*:*:*:*
cisco ios 15.0\(2\)se10a cpe:2.3:o:cisco:ios:15.0\(2\)se10a:*:*:*:*:*:*:*
cisco ios 15.0\(2\)se11 cpe:2.3:o:cisco:ios:15.0\(2\)se11:*:*:*:*:*:*:*
cisco ios 15.0\(2\)se12 cpe:2.3:o:cisco:ios:15.0\(2\)se12:*:*:*:*:*:*:*
cisco ios 15.0\(2\)se13 cpe:2.3:o:cisco:ios:15.0\(2\)se13:*:*:*:*:*:*:*
cisco ios 15.0\(2\)se13a cpe:2.3:o:cisco:ios:15.0\(2\)se13a:*:*:*:*:*:*:*
cisco ios 15.0\(2\)se13b cpe:2.3:o:cisco:ios:15.0\(2\)se13b:*:*:*:*:*:*:*
cisco ios 15.0\(2a\)ex5 cpe:2.3:o:cisco:ios:15.0\(2a\)ex5:*:*:*:*:*:*:*
cisco ios 15.0\(2a\)se9 cpe:2.3:o:cisco:ios:15.0\(2a\)se9:*:*:*:*:*:*:*
cisco ios 15.1\(1\)sy cpe:2.3:o:cisco:ios:15.1\(1\)sy:*:*:*:*:*:*:*
cisco ios 15.1\(1\)sy1 cpe:2.3:o:cisco:ios:15.1\(1\)sy1:*:*:*:*:*:*:*
cisco ios 15.1\(1\)sy2 cpe:2.3:o:cisco:ios:15.1\(1\)sy2:*:*:*:*:*:*:*
cisco ios 15.1\(1\)sy3 cpe:2.3:o:cisco:ios:15.1\(1\)sy3:*:*:*:*:*:*:*
cisco ios 15.1\(1\)sy4 cpe:2.3:o:cisco:ios:15.1\(1\)sy4:*:*:*:*:*:*:*
cisco ios 15.1\(1\)sy5 cpe:2.3:o:cisco:ios:15.1\(1\)sy5:*:*:*:*:*:*:*
cisco ios 15.1\(1\)sy6 cpe:2.3:o:cisco:ios:15.1\(1\)sy6:*:*:*:*:*:*:*
cisco ios 15.1\(2\)sy cpe:2.3:o:cisco:ios:15.1\(2\)sy:*:*:*:*:*:*:*
cisco ios 15.1\(2\)sy1 cpe:2.3:o:cisco:ios:15.1\(2\)sy1:*:*:*:*:*:*:*
cisco ios 15.1\(2\)sy2 cpe:2.3:o:cisco:ios:15.1\(2\)sy2:*:*:*:*:*:*:*
cisco ios 15.1\(2\)sy3 cpe:2.3:o:cisco:ios:15.1\(2\)sy3:*:*:*:*:*:*:*
cisco ios 15.1\(2\)sy4 cpe:2.3:o:cisco:ios:15.1\(2\)sy4:*:*:*:*:*:*:*
cisco ios 15.1\(2\)sy4a cpe:2.3:o:cisco:ios:15.1\(2\)sy4a:*:*:*:*:*:*:*
cisco ios 15.1\(2\)sy5 cpe:2.3:o:cisco:ios:15.1\(2\)sy5:*:*:*:*:*:*:*
cisco ios 15.1\(2\)sy6 cpe:2.3:o:cisco:ios:15.1\(2\)sy6:*:*:*:*:*:*:*
cisco ios 15.1\(2\)sy7 cpe:2.3:o:cisco:ios:15.1\(2\)sy7:*:*:*:*:*:*:*
cisco ios 15.1\(2\)sy8 cpe:2.3:o:cisco:ios:15.1\(2\)sy8:*:*:*:*:*:*:*
cisco ios 15.1\(2\)sy9 cpe:2.3:o:cisco:ios:15.1\(2\)sy9:*:*:*:*:*:*:*
cisco ios 15.1\(2\)sy10 cpe:2.3:o:cisco:ios:15.1\(2\)sy10:*:*:*:*:*:*:*
cisco ios 15.1\(2\)sy11 cpe:2.3:o:cisco:ios:15.1\(2\)sy11:*:*:*:*:*:*:*
cisco ios 15.1\(2\)sy12 cpe:2.3:o:cisco:ios:15.1\(2\)sy12:*:*:*:*:*:*:*
cisco ios 15.1\(2\)sy13 cpe:2.3:o:cisco:ios:15.1\(2\)sy13:*:*:*:*:*:*:*
cisco ios 15.1\(2\)sy14 cpe:2.3:o:cisco:ios:15.1\(2\)sy14:*:*:*:*:*:*:*
cisco ios 15.1\(2\)sy15 cpe:2.3:o:cisco:ios:15.1\(2\)sy15:*:*:*:*:*:*:*
cisco ios 15.1\(2\)sy16 cpe:2.3:o:cisco:ios:15.1\(2\)sy16:*:*:*:*:*:*:*
cisco ios 15.1\(2\)sy16a cpe:2.3:o:cisco:ios:15.1\(2\)sy16a:*:*:*:*:*:*:*

References for CVE-2021-34699

cvelogic Threat Intelligence