CVE-2026-55674 — CRITICAL (9.3)

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.

CVSS Score

9.3

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

NONE

User Interaction

REQUIRED

Scope

CHANGED

Confidentiality

HIGH

Integrity

HIGH

Availability

NONE

Related Weaknesses (CWE)

CWE-79

References

https://github.com/discourse/discourse/security/advisories/GHSA-qx4v-rg4v-pm2g

FAQ

What is CVE-2026-55674?

CVE-2026-55674 is a vulnerability with a CVSS score of 9.3 (CRITICAL). 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_sc...

How severe is CVE-2026-55674?

CVE-2026-55674 has been rated CRITICAL with a CVSS base score of 9.3/10. This is considered a critical vulnerability requiring immediate attention.

Is there a patch for CVE-2026-55674?

Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.