CVE-2026-55674

Discourse: Cache poisoning/XSS via color scheme cookies

Published: Aug 17, 2026Updated: Sep 18, 2026 Sources: CVE List NVDCWE-79

9.3CRITICAL

Description

Discourse is an open-source discussion platform. Prior to 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0, an unauthenticated attacker could send a single request with a crafted color_scheme_id (or dark_scheme_id) cookie to inject arbitrary HTML into a Discourse page. Because the cookie value was rendered into a color scheme tag without escaping, the attacker could break out of the attribute and inject a tag that bypassed Discourse's nonce-based Content Security Policy, resulting in arbitrary JavaScript execution in visitors' browsers. This issue is fixed in versions 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0.

No summary for this CVE yet.

CVSS Vector Breakdown

Exploitability

AV:NAttack Vector

Network

AC:LAttack Complexity

Low

PR:NPrivileges Required

None

UI:RUser Interaction

Required

Scope

S:CScope

Changed

Impact

C:HConfidentiality

High

I:HIntegrity

High

A:NAvailability

None

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Weaknesses

CWE-79

Affected Products

discourse

commercial·USaka discourse.org

discourse

Web & CMS Plugins

Exploitability

No known exploits, KEV entries, or remediation guidance available for this vulnerability yet.

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Attack Graph

Products CVE Techniques Tactics

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MITRE ATT&CK

2 techniques

Execution

Initial Access

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References

https://github.com/discourse/discourse/security/advisories/GHSA-qx4v-rg4v-pm2g

github.com

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