CVE-2023-26040Network attack vector

Stored XSS via unescaped chat excerpt tags

Published Mar 17, 2023 · Updated Feb 25, 2025

Cross-site scripting in Discourse tests-passed builds after 3.1.0.beta2 and before 3.1.0.beta3 allows remote attackers to execute script. The replace-emoji helper passed chat excerpt text to htmlSafe without first escaping non-Markdown tags, causing Ember to render attacker-controlled markup. Exploitation requires a user to edit the malicious chat message or reply to it, after which the injected script runs in the Discourse browser origin.

CVSS severity6.5
Medium
EPSS probability0.35%
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 tests-passed builds after 3.1.0.beta2 and before 3.1.0.beta3 allows remote attackers to execute script. The replace-emoji helper passed chat excerpt text to htmlSafe without first escaping non-Markdown tags, causing Ember to render attacker-controlled markup. Exploitation requires a user to edit the malicious chat message or reply to it, after which the injected script runs in the Discourse browser origin.

The record

CVE
CVE-2023-26040
Published
Mar 17, 2023
Updated
Feb 25, 2025
Vendor
Discourse
Product
Discourse
Classifications
CWE-79, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 17, 2023CVE publishedPublication date reported by the CVE source.
  2. Feb 25, 2025Record 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=tests-passed > 3.1.0.beta2, < 3.1.0.beta3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Discourse · Discourseversion=tests-passed > 3.1.0.beta2, < 3.1.0.beta3

Published CVSS scores

6.1NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
6.5GitHub CNACVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L

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')
T1203Exploitation for Client 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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