CVE-2026-55674
CriticalCVSS 9.3Summary
Prior to versions 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0 in Discourse, 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.
Risk Assessment
An attacker can execute arbitrary scripts in users' browsers, potentially leading to session theft, account takeover, or malware distribution.
Recommendation
Update Discourse to versions 2026.1.6, 2026.5.2, 2026.6.1, or 2026.7.0, which include the fix.
Original NVD description (English source)
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.