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Vulnerabilities CVE-2026-55674

CVE-2026-55674

Critical
Open
TLP:CLEAR

Discourse: Cache poisoning/XSS via color scheme cookies

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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.

Details

CVSS Score
9.3
EPSS Score
0.34%

26.6th percentile

CVSS Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N
Confidence
90%
Published
Aug 17, 2026
Last Modified
Aug 18, 2026
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