CVE-2026-55674: XSS
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 colorschemeid (or darkschemeid) 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 Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Discourseto a version that resolves this vulnerability.Fixed in 2026.1.6 - Upgrade
Upgrade
Discourseto a version that resolves this vulnerability.Fixed in 2026.5.2 - Upgrade
Upgrade
Discourseto a version that resolves this vulnerability.Fixed in 2026.6.1 - Upgrade
Upgrade
Discourseto a version that resolves this vulnerability.Fixed in 2026.7.0
Event History
Frequently Asked Questions
What is the severity of CVE-2026-55674?
CVE-2026-55674 has a severity rating of critical with a CVSS score of 9.3.
How do I fix CVE-2026-55674?
To mitigate CVE-2026-55674, update Discourse to versions 2026.1.6, 2026.5.2, 2026.6.1, or 2026.7.0.
What type of vulnerability is CVE-2026-55674?
CVE-2026-55674 is identified as a Cross-Site Scripting (XSS) vulnerability.
Who is affected by CVE-2026-55674?
Any Discourse user running versions prior to 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0 is at risk from CVE-2026-55674.
What is the impact of CVE-2026-55674?
CVE-2026-55674 allows unauthenticated attackers to inject arbitrary HTML into Discourse pages due to a flaw in cookie handling.