CVE-2021-41095Network attack vector

XSS via unescaped watched-word error interpolation

Published Sep 27, 2021 · Updated Aug 4, 2024

Cross-site scripting in Discourse 2.7.7 and earlier and 2.8.0.beta1 through 2.8.0.beta6 allows remote attackers to execute JavaScript. NewPostManager and WatchedWordsValidator insert matched blocked words into localized error strings without HTML escaping before browser rendering. Exploitation requires an HTML-tag watched word, a modified or disabled default Content Security Policy, and a user who renders the crafted error; script execution can read or alter browser-accessible forum data.

CVSS severity4.2
Medium
EPSS probability0.58%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in Discourse 2.7.7 and earlier and 2.8.0.beta1 through 2.8.0.beta6 allows remote attackers to execute JavaScript. NewPostManager and WatchedWordsValidator insert matched blocked words into localized error strings without HTML escaping before browser rendering. Exploitation requires an HTML-tag watched word, a modified or disabled default Content Security Policy, and a user who renders the crafted error; script execution can read or alter browser-accessible forum data.

The record

CVE
CVE-2021-41095
Published
Sep 27, 2021
Updated
Aug 4, 2024
Vendor
Discourse
Product
Discourse
Classifications
CWE-79, T1059.007
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 27, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=<= 2.7.7
  2. Affected versionversion=>= 2.8.0.beta1, <= 2.8.0.beta6

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Discourse · Discourseversion=<= 2.7.7; version=>= 2.8.0.beta1, <= 2.8.0.beta6

Published CVSS scores

4.2GitHub, Inc.CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:N
4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/A:N
6.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1059.007Command and Scripting Interpreter: JavaScript

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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