CVE-2021-20843Network attack vector

Router setting changes via cross-site script inclusion

Published Nov 24, 2021 · Updated Aug 3, 2024

Cross-site script inclusion in Yamaha RTX830, NVR510, NVR700W, and RTX1210 Web GUIs allows remote authenticated users to alter settings. While a GUI session is open, a malicious external page triggers unintended Web GUI functions in the authenticated browser; Yamaha has not identified the affected handler. Exploitation requires a logged-in administrator to visit the attacker-controlled page, and the resulting action can change router configuration.

CVSS severity4.8
Medium
EPSS probability0.67%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site script inclusion in Yamaha RTX830, NVR510, NVR700W, and RTX1210 Web GUIs allows remote authenticated users to alter settings. While a GUI session is open, a malicious external page triggers unintended Web GUI functions in the authenticated browser; Yamaha has not identified the affected handler. Exploitation requires a logged-in administrator to visit the attacker-controlled page, and the resulting action can change router configuration.

The record

CVE
CVE-2021-20843
Published
Nov 24, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-829, T1204
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Nov 24, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

3.5NIST NVDAV:N/AC:M/Au:S/C:N/I:P/A:N
5.4NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
4.8JPCERT/CC JVNCVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:N/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-829Inclusion of Functionality from Untrusted Control Sphere
T1204User Execution

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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