What’s Vulnerable › Vulnerabilities

CVE-2026-27740: Discourse has Stored XSS in AI Triage Automation

• Severity: medium (CVSS 6.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-03-19 · updated 2026-06-17
• Weakness: CWE-79

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.

Affected products

• discourse: from 2026.1.0 before 2026.1.2; from 2026.2.0 before 2026.2.1; 2026.3.0 — fixed in 2026.1.2, 2026.2.1

How to fix

Upgrade to a fixed version: discourse 2026.1.2, 2026.2.1. Check the vendor advisory for mitigations.

References

• https://github.com/discourse/discourse/commit/44b84439df7e4424b2e7f216fd8fdd7dacff2227
• https://github.com/discourse/discourse/commit/8ae7cb2414d6918d7fc45e1fda7ffbb32912a975
• https://github.com/discourse/discourse/commit/ed70949f2c047196f33cfa94f2819df29c5d1e5f
• https://github.com/discourse/discourse/security/advisories/GHSA-95hc-42c6-wvvr

Get alerted when CVE-2026-27740 or the next vulnerability affects your stack