CVE-2026-27740 Discourse — Exploit & Vulnerability Details MEDIUM

Parameter	Value
CVSS	5.1 (MEDIUM)
Affected Versions	2026.1.0 — 2026.2.1
Fixed In	2026.1.2
Type	CWE-79 (Cross-Site Scripting (XSS))
Vendor	Discourse
Public PoC	No

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.

Attack Parameters

Attack Vector

Network

Can be exploited remotely

Attack Complexity

Low

Easy to exploit

Attack Requirements

None

No additional conditions

Privileges Required

Low

Basic privileges needed

User Interaction

Passive

Minimal interaction

Impact Assessment

Confidentiality

Low

Partial data leak

Integrity

Low

Partial data modification

Availability

None

No disruption

CVSS Vector v4.0

Weakness Type (CWE)

CWE-79 Cross-Site Scripting (XSS)

Vulnerable Products 3

Configuration	From (including)	Up to (excluding)
Discourse Discourse cpe:2.3:a:discourse:discourse::::::::	`2026.1.0`	`2026.1.2`
Discourse Discourse cpe:2.3:a:discourse:discourse::::::::	`2026.2.0`	`2026.2.1`
Discourse Discourse cpe:2.3:a:discourse:discourse:2026.3.0::::latest:::	—	—