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CVE-2026-55674— Discourse: Cache poisoning/XSS via color scheme cookies

CVSS 9.3 · Critical
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I. Basic Information for CVE-2026-55674

Vulnerability Information
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Vulnerability Title
Discourse: Cache poisoning/XSS via color scheme cookies
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
在Web页面生成时对输入的转义处理不恰当(跨站脚本)
Source: CVE Program / CVE List V5

Affected Products

VendorProductAffected VersionsCPESubscribe
discoursediscourse < 2026.1.6 -

II. Public POCs for CVE-2026-55674

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III. Intelligence Information for CVE-2026-55674

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Vendor Advisories for CVE-2026-55674 (1)

Same Patch Batch · discourse · 2026-08-17 · 4 CVEs total

CVE-2026-539605.3 MEDIUMDiscourse: Hidden first-post excerpt is emitted in Q&A schema JSON-LD
CVE-2026-557044.3 MEDIUMDiscourse: Shared-draft titles and excerpts leak through group post serialization
CVE-2026-598294.3 MEDIUMDiscourse: Review queue exposes flag-related private message excerpts to category group mo

IV. Related Vulnerabilities

Same product: discourse
Same vendor: discourse
Same weakness: CWE-79

V. Comments for CVE-2026-55674

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