CVE-2026-27740

CVE Enrichment

CVSS: 5.1 MEDIUM
EPSS: 0.34%
EPSS Percentile: 28.24%
CISA KEV: Not listed

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.

Technical Details

CVSS Version: 4.0
CNA / NVD Source: [email protected]
Published: 20-Mar-2026 04:17
Last Modified: 17-Jun-2026 17:27
EPSS Date: 2026-11-10
CWE: CWE-79

CVSS Vector


            CVSS:4.0                            AV:N /
                            AC:L /
                            AT:N /
                            PR:L /
                            UI:P /
                            VC:L /
                            VI:L /
                            VA:N /
                            SC:L /
                            SI:L /
                            SA:N /
                            E:X /
                            CR:X /
                            IR:X /
                            AR:X /
                            MAV:X /
                            MAC:X /
                            MAT:X /
                            MPR:X /
                            MUI:X /
                            MVC:X /
                            MVI:X /
                            MVA:X /
                            MSC:X /
                            MSI:X /
                            MSA:X /
                            S:X /
                            AU:X /
                            R:X /
                            V:X /
                            RE:X /
                            U:X

CNA Products / Version Status

discourse · discourse Source: CNA · [email protected]
Default status: unknown

>= 2026.1.0-latest, < 2026.1.2 — affected
>= 2026.2.0-latest, < 2026.2.1 — affected
= 2026.3.0-latest — affected

Affected Products / Versions

discourse / discourse Source: NVD CPE · affected
Version / affected range: * · from (inclusive) 2026.1.0 · before (exclusive) 2026.1.2
cpe:2.3:a:discourse:discourse:*:*:*:*:*:*:*:*
discourse / discourse Source: NVD CPE · affected
Version / affected range: * · from (inclusive) 2026.2.0 · before (exclusive) 2026.2.1
cpe:2.3:a:discourse:discourse:*:*:*:*:*:*:*:*
discourse / discourse Source: NVD CPE · affected
Version / affected range: 2026.3.0
cpe:2.3:a:discourse:discourse:2026.3.0:*:*:*:latest:*:*:*

References

Last enrichment sync: 12-Nov-2026 20:37
Sources: NVD · FIRST EPSS · CISA KEV
Latest successful provider update; providers refresh independently.

Reported Context (1)

CVE-2026-27740 enabled stored XSS via LLM generated content in Discourse. OWASP’s 2026 LLM Top 10 Adds Incident Data to AI Risk Rankings

CVE (1)

People (1)

Threat Actors (1)

MITRE ATT&CK (2)

Vendors (6)

Products (10)

Tools (2)

Industries (1)

Countries (1)

Note: Related entities, including threat actors, malware, CVEs, MITRE ATT&CK techniques, vendors, products, tools, countries, and industries, are shown when they appear in the same reporting. Their presence does not necessarily mean they were targeted, compromised, vulnerable, responsible for the activity, or directly involved in the incident.