by Kastro
Paper/Archive/CVE-2026-55674

CVE-2026-55674

discourse discourse — Discourse: Cache poisoning/XSS via color scheme cookies

EPSS 0.6%CVSS 9.3
critical.is priorityof 100
38
CVSS 9.3 (CNA)9.3 / 10 × 3027.9Not in CISA KEV+300.0EPSS percentile 48.2.482 × 209.6No public exploit+100.0SSVC exploitation: none+100.0
Description · from the CVE record

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

ProductAffectedFixed inSource
discourse< 2026.1.6–CNA
discourse>= 2026.5.0-latest, < 2026.5.2–CNA
discourse>= 2026.6.0-latest, < 2026.6.1–CNA

Scores by source

GitHub_M (CNA)9.3CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N
CISA ADPSSVCExploitation: none · Automatable: no · Technical impact: total

References

refgithub.com/discourse/discourse/security/advisories/GHSA-qx4v-rg4v-pm2g