No exploitation reported

CVE-2021-40120

No exploitation reported by the sources we read.

Published2021-11-04
WeaknessCWE-20 · CWE-78

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

A vulnerability in the web-based management interface of certain Cisco Small Business RV Series Routers could allow an authenticated, remote attacker with administrative privileges to inject arbitrary commands into the underlying operating system and execute them using root-level privileges. This vulnerability is due to insufficient validation of user-supplied input. An attacker could exploit this vulnerability by sending malicious input to a specific field in the web-based management interface of an affected device. A successful exploit could allow the attacker to execute arbitrary commands on the underlying Linux operating system as a user with root-level privileges.

Timeline

dates in UTC

2021-11-0416:15CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 21:37 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-40120?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-40120?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD

Cisco application extension platform

Branch	Affected	Fixed in	Source
1.5	= 1.5.1.13	no fix published	NVD

Cisco ios xrversion to verify

Branch	Affected	Fixed in	Source
4.2	= 4.2.3.06	no fix published	NVD

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

Advisories and patches

tools.cisco.comVendor Advisory

Detection

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: none listed

Sources

CISA-ADPSSVC decisionnone2024-11-07
OpenCVESSVC decisionnone—
CNACVSS 3.16.5read 2026-10-23
NVDCVSS 3.17.2read 2026-10-23
NVDCVSS 2.09read 2026-10-23
CNAweakness (CWE)CWE-20read 2026-10-23
NVDweakness (CWE)CWE-78read 2026-10-23
FIRST EPSSEPSS score2.0 %2026-10-22

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
Published: 2021-11-04
Last Modified: 2026-06-17
NVD status: Modified

Frequently asked questions

What is CVE-2021-40120?

Is CVE-2021-40120 actively exploited?

Active exploitation of CVE-2021-40120 has not been confirmed. Its EPSS score was 2.0% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-40120?

CVE-2021-40120 has a CVSS v3 base score of 7.2 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H.

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