- CVSS
- MEDIUM · 6.1v3.1CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
- Published
- 2026-03-19
- Weakness
- CWE-79
- Source
- nvd.nist.gov/vuln/detail/CVE-2026-27740
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.
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
How GTK Cyber trains on this
AI security training at GTK Cyber covers the LLM and ML-pipeline vulnerability classes that vulnerabilities like CVE-2026-27740 fall into. Our hands-on courses are taught by Charles Givre and other practitioners who break and defend production AI systems.