CVE-2021-20844Network attack vector

Authenticated information disclosure via response header injection

Published Nov 24, 2021 · Updated Aug 3, 2024

HTTP response header injection in Yamaha router Web GUIs allows remote authenticated users to obtain sensitive information through a crafted page. Public advisories do not identify the affected header or the Web GUI operation that places untrusted scripting syntax into it. Exploitation requires a logged-in user to view an attacker-controlled page, and the disclosed information is unspecified.

CVSS severity5.7
Medium
EPSS probability0.93%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

HTTP response header injection in Yamaha router Web GUIs allows remote authenticated users to obtain sensitive information through a crafted page. Public advisories do not identify the affected header or the Web GUI operation that places untrusted scripting syntax into it. Exploitation requires a logged-in user to view an attacker-controlled page, and the disclosed information is unspecified.

The record

CVE
CVE-2021-20844
Published
Nov 24, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-644, T1189
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

Compare your product and version with the public record. A matching version still requires validation against your environment.

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

5.7NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:N/A:N
3.7JPCERT/CCCVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:L/I:L/A:N
3.5NIST NVDAV:N/AC:M/Au:S/C:P/I:N/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-644Improper Neutralization of HTTP Headers for Scripting Syntax
T1189Drive-by Compromise

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

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo