ReviewCritical

CVE-2026-55674

discourse

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...

CVSS: 9.3
EPSS: -
CISA KEV: Not listed
Published: 2026.08.18

PRIORITY ASSESSMENT

Review

The CVSS severity warrants an early asset and exposure review.

Known exploitationNot established by KEV

Exploit probability-

Technical severityCVSS 9.3

Vulnerability overview

Affected product and versions

Product: discourse
Affected versions: < 2026.1.6, >= >= 2026.5.0-latest, < 2026.5.2, >= >= 2026.6.0-latest, < 2026.6.1
Fixed versions: No verified fixed-version field is available yet

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide

1
Identify
Confirm that discourse and an affected version are present.
2
Prioritize
Combine exploitation signals with asset exposure and business criticality.
3
Remediate
Follow the vendor advisory or supported update path and preserve rollback options.
4
Verify
Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N
CWE: CWE-79