Discourse: Cache poisoning/XSS via color scheme cookies

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-55674
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-17 16:16:58 UTC
Updated2026-08-18 15:16:55 UTC
DescriptionDiscourse 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.

Risk And Classification

Primary CVSS: v3.1 9.3 CRITICAL from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N

EPSS: 0.003370000 probability, percentile 0.265980000 (date 2026-08-18)

Problem Types: CWE-79 | CWE-79 CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary9.3CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N
3.1CNADECLARED9.3CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Changed
Confidentiality
High
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Discourse Discourse affected < 2026.1.6 Not specified
CNA Discourse Discourse affected >= 2026.5.0-latest, < 2026.5.2 Not specified
CNA Discourse Discourse affected >= 2026.6.0-latest, < 2026.6.1 Not specified

References

ReferenceSourceLinkTags
github.com/discourse/discourse/security/advisories/GHSA-qx4v-rg4v-pm2g [email protected] github.com
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

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