CVE-2026-55674
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.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.36%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
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 3.1
- 9.3 CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N
- EPSS
- 0.36% probability · 29th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-79
- Source
- security-advisories@github.com
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.