CVE-2026-27740: Discourse has Stored XSS in AI Triage Automation
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.
Affected Software
Remediation
Event History
Frequently Asked Questions
What is the severity of CVE-2026-27740?
CVE-2026-27740 is classified as a medium severity vulnerability due to its potential for exploitation through stored XSS.
How do I fix CVE-2026-27740?
To fix CVE-2026-27740, upgrade Discourse to versions 2026.3.0-latest.1, 2026.2.1, or 2026.1.2 or later.
What products are affected by CVE-2026-27740?
CVE-2026-27740 affects Discourse versions prior to 2026.3.0-latest.1, 2026.2.1, and 2026.1.2.
What type of vulnerability is CVE-2026-27740?
CVE-2026-27740 is a stored cross-site scripting (XSS) vulnerability due to untrusted output from an AI Large Language Model.
How can CVE-2026-27740 be exploited?
CVE-2026-27740 can be exploited by an attacker inserting malicious scripts that are then stored and executed in the context of the victim's browser.