CVE-2026-27740 Details
Description
Discourse is an open-source discussion platform. Versions prior to 2026.3.0-latest.1, 2026.2.1, and 2026.1.2 have a cross-site scripting vulnerability that arises because the system trusts the raw output from an AI Large Language Model (LLM) and renders it using htmlSafe in the Review Queue interface without adequate sanitization. A malicious attacker can use valid Prompt Injection techniques to force the AI to return a malicious payload (e.g., tags). When a Staff member (Admin/Moderator) views the flagged post in the Review Queue, the payload executes. Versions 2026.3.0-latest.1, 2026.2.1, and 2026.1.2 contain a patch. As a workaround, temporarily disable AI triage automation scripts.
A cross-site scripting vulnerability has been identified in Discourse, an open-source discussion platform. This issue affects versions prior to 2026.3.0-latest.1, 2026.2.1, and 2026.1.2. The vulnerability arises because the system improperly trusts raw output from an AI Large Language Model (LLM), rendering it in the Review Queue interface using htmlSafe without sufficient sanitization. Malicious attackers can exploit this by using valid Prompt Injection techniques to manipulate the AI into delivering harmful payloads, such as tags. When a Staff member (Admin or Moderator) reviews the flagged post, the injected payload executes, leading to a stored cross-site scripting vulnerability.
Users can upgrade to Discourse versions 2026.3.0-latest.1, 2026.2.1, or 2026.1.2, all of which include the necessary patch. Alternatively, AI triage automation scripts can be temporarily disabled.
Metrics
CVSS 4.0 Severity and Vector Strings:
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
CISA-ADP
Assessed Mar 20, 2026References to Advisories, Solutions, and Tools
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Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-79 | Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| discourse discourse | >= 2026.1.0, < 2026.1.2 >= 2026.2.0, < 2026.2.1 2026.3.0 |
CPE
Remediation
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Change History
4 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jun 17, 2026 | CVE Modified | [email protected] |
| Jun 17, 2026 | CVE Modified | CISA-ADP |
| Mar 25, 2026 | Initial Analysis | [email protected] |
| Mar 19, 2026 | New CVE Received | [email protected] |