# CVE-2026-55674 — discourse

> As of 2026-08-18, CVE-2026-55674 is a CRITICAL-severity vulnerability in discourse, CVSS v3.1 9.3, EPSS 0.5% (46.6th percentile). No Threadlinqs-tracked threat campaign has been attributed to CVE-2026-55674 as of 2026-08-18; the identifier is re-checked against the Threadlinqs threat corpus on every daily ingest.

**Last updated:** 2026-08-18

## What is CVE-2026-55674?

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.

The record classifies CVE-2026-55674 under weakness class [CWE-79](https://intel.threadlinqs.com/cwe/CWE-79). Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs a user to take an action first, and has high impact on confidentiality, integrity. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 56 days ago.

## Severity and exploitation probability

- **CVSS v3.1 base score:** 9.3 — CRITICAL (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N`)
- **EPSS (FIRST):** 0.5% probability of exploitation in the next 30 days, higher than 46.6% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 6.5/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-08-17, last modified 2026-08-18

## Is CVE-2026-55674 being exploited?

It currently carries a trending score of 33 in the Threadlinqs vulnerability feed.

## Affected products and versions

- **discourse**: discourse

## How to fix CVE-2026-55674

No vendor patch reference has been recorded for CVE-2026-55674 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-55674

No threat campaign in the Threadlinqs corpus currently references CVE-2026-55674, in its CVE list or as an indicator. The linkage is recomputed from the live corpus on every daily ingest, so this section fills in as soon as a tracked campaign cites the identifier.

## Sources

Enriched from CVE.org, NVD, FIRST EPSS. Last verified by Threadlinqs on 2026-10-12. This product uses the NVD API but is not endorsed or certified by the NVD.

**Vendor advisory and patch**

- [github.com](https://github.com/discourse/discourse/security/advisories/GHSA-qx4v-rg4v-pm2g)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-55674
Full detection coverage and IOCs for threats exploiting CVE-2026-55674 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp