CVE-2026-55674
Discourse: Cache poisoning/XSS via color scheme cookies
- State
- Published
- Severity
- 9.3 Critical
- Published
- Aug 17, 2026
- Updated
- Aug 18, 2026
- Reserved
- Jun 17, 2026
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 3.1 | 9.3 Critical | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N | GitHub_M |
Weaknesses
- CWE-79 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Affected Products
| Product | Versions |
|---|---|
discoursediscourse |
|
References
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