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Untriaged
Permalink CVE-2026-55674
9.3 CRITICAL
  • CVSS version (CVSS): 3.1
  • Attack Vector (AV): Network (N)
  • Attack Complexity (AC): Low (L)
  • Privileges Required (PR): None (N)
  • User Interaction (UI): Required (R)
  • Scope (S): Changed (C)
  • Confidentiality (C): High (H)
  • Integrity (I): High (H)
  • Availability (A): None (N)
  • Modified Attack Vector (MAV): Network (N)
  • Modified Attack Complexity (MAC): Low (L)
  • Modified Privileges Required (MPR): None (N)
  • Modified User Interaction (MUI): Required (R)
  • Modified Confidentiality (MC): High (H)
  • Modified Scope (MS): Changed (C)
  • Modified Integrity (MI): High (H)
  • Modified Availability (MA): None (N)
created 6 days, 18 hours ago Activity log
  • Created suggestion 6 days, 18 hours ago
Discourse: Cache poisoning/XSS via color scheme cookies

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.

Affected products

discourse
  • ==>= 2026.6.0-latest, < 2026.6.1
  • ==>= 2026.5.0-latest, < 2026.5.2
  • ==< 2026.1.6

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