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CVE-2026-55674

Discourse: Cache poisoning/XSS via color scheme cookies

Critical9.3EPSS 0.59%
Published
Updated
Reserved
Assigned by
GitHub_M

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.

Scores

CVSS scores of CVE-2026-55674, by who scored it
Scored byCVSSScoreVector
GitHub_MCNA (assigner)3.1Critical9.3CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N
NVDNVD · Deferred3.1Critical9.3CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N
EPSS (exploitation in 30 days)
0.59% · top 52% of all CVEs (6 Nov 2026)
CISA SSVC
Exploitation: none · Automatable: no · Technical impact: total
Loading the EPSS history…

The list uses the assigner's score when there is one, then CISA's, then NVD's: Critical 9.3.

Weakness

Affected products

  • discourse · discourse

    • affected < 2026.1.6
    • affected >= 2026.5.0-latest, < 2026.5.2
    • affected >= 2026.6.0-latest, < 2026.6.1

References (1)

Sources

The same CVE in the primary databases and aggregators, to check against.

Badge for a README or a ticket

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Record last updated .