What is the CVSS score of CVE-2026-27740?

CVE-2026-27740 has a CVSS 3.1 base score of 6.1 (Medium). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N. EPSS exploitation probability: 0.0%.

How to fix or mitigate CVE-2026-27740?

Within 30 days: Identify affected systems and apply vendor patches as part of regular patch cycle. Verify Content-Security-Policy and output encoding.

Discourse CVE-2026-27740

Q: Which versions of Discourse are affected by CVE-2026-27740?

Organizations using Discourse should be aware of moderate risk from CVE-2026-27740, a cross-site scripting vulnerability rated CVSS 6.1.. A patch is available.

EUVD-2026-13194 MEDIUM

Cross-site Scripting (XSS) (CWE-79)

2026-03-19 security-advisories@github.com

XSS Discourse

6.1

CVSS 3.1 · GitHub Advisory

View

Vulnerability Assessment

Weakness	CWE CWE-79 OWASP Top 10:2025 A05:2025 - Injection ASVS 5.0 V1 - Encoding and Sanitization Output encoding, context-aware escaping MITRE ATT&CK 2 techniques across 2 tactics: Initial Access, Execution The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. Sign in to read
Impact	Attackers can steal session cookies, redirect users to malicious sites, deface content, or perform actions on behalf of authenticated users.
Exploit ScenarioDerived	An attacker injects a JavaScript payload into a vulnerable input field. When another user views the page, the script executes in their browser, stealing their session token.

This Month Plan within 30 days. Why: MEDIUM severity (CVSS 4.0-6.9).

Patch available 0.0% exploitation probability (EPSS)

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AnalysisAIv1 – Mar 19, 2026

Cross-site scripting in Discourse's Review Queue interface allows remote attackers to inject malicious payloads through prompt injection attacks against the AI triage system, which renders unsanitized LLM output to staff members. When administrators or moderators view flagged posts, the injected payload executes in their browser context, potentially compromising their sessions or performing unauthorized actions. The vulnerability affects Discourse versions prior to 2026.3.0-latest.1, 2026.2.1, and 2026.1.2, with patches available in these releases.

Earlier versions of this analysis (1)

v1 Mar 19, 2026 - 21:30 CVSS 6.1

RemediationAI

Encode all user-supplied output contextually (HTML, JS, URL). Implement Content Security Policy (CSP) headers. Use HTTPOnly and Secure cookie flags.

Affected VersionsENISA

discourse = 2026.3.0-latest

discourse 2026.1.0-latest, < 2026.1.2

discourse 2026.2.0-latest, < 2026.2.1

Affected Packages

euvd discourse no fix

euvd discourse_2026_1_0_latest fix: 2026.1.2

euvd discourse_2026_2_0_latest fix: 2026.2.1

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 3 packages in euvd

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

Cross-site scripting (XSS) allows injection of client-side scripts into web pages viewed by other users due to insufficient output encoding.

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

GitHub Advisory PRIMARY 6.1 MEDIUM

AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Primary rating from GitHub Advisory · only source for this CVE.

CVSS VectorGitHub Advisory

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Scope

Changed

Confidentiality

Low

Integrity

Low

Availability

None

Lifecycle Timeline

Patch available

Apr 16, 2026 - 05:29 EUVD

2026.1.2,2026.2.1

CVE Published

Mar 19, 2026 - 21:17 nvd

MEDIUM 6.1

DescriptionGitHub Advisory

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.

Executive ViewAI

Why It Matters

Organizations using Discourse should be aware of moderate risk from CVE-2026-27740, a cross-site scripting vulnerability rated CVSS 6.1. Attackers could inject scripts to steal sessions or perform actions as authenticated users. Organizations should apply vendor updates when available and monitor for exploitation.

Business Impact: Low

Compensating Controls

Apply vendor patch. If patching is delayed: implement CSP headers, enable HttpOnly cookies, deploy WAF XSS rules.

Threat Intelligence Overview

EPSS Score

0.0%

Top 86% exploitable

Data Quality

6 sources

Confidence: High

EUVD

NVD

CVE.org

EPSS

GitHub

VulDB

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue

Severity MEDIUM

CISA KEV No

Public POC No

EPSS 0.0%

Patch available Yes

Active threat No

Deciding rule

MEDIUM severity (CVSS 4.0-6.9)

What every action level means

Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.

Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.

This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.

This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.

Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived

Defer

Exploitation· derived

None

System Exposure· derived

Open

Automatable· derived

Human Impact

Low

Priority Score

Low Medium High Critical

KEV: 0

EPSS: 0

CVSS: +30

PoC: 0

Weaponized: 0

Threat intel: 0

Gov advisory: 0

Attack Technique

Cross-Site Scripting MEDIUM

Cross-Site Scripting occurs when an application accepts untrusted data and sends it to a web browser without proper validation or encoding.

More in Discourse

View all

CVE-2025-48954 HIGH Act Now POC

8.1 Jun 25

Discourse versions prior to 3.5.0.beta6 contain a reflected cross-site scripting (XSS) vulnerability in social login fun

CVE-2022-46162 CRITICAL Act Now POC

9.8 Nov 30

discourse-bbcode is the official BBCode plugin for Discourse. Rated critical severity (CVSS 9.8), this vulnerability is

CVE-2026-27934 HIGH This Week POC

8.7 Mar 19

Unauthorized information disclosure in Discourse discussion platform versions prior to 2026.3.0-latest.1, 2026.2.1, and

CVE-2024-47773 HIGH This Week POC

8.2 Oct 08

Discourse is an open source platform for community discussion. Rated high severity (CVSS 8.2), this vulnerability is rem

CVE-2026-26265 HIGH This Week POC

7.5 Feb 26

Discourse versions prior to 2025.12.2, 2026.1.1, and 2026.2.0 contain an insecure direct object reference (IDOR) in the

CVE-2021-3138 HIGH This Week POC

7.5 Jan 14

In Discourse 2.7.0 through beta1, a rate-limit bypass leads to a bypass of the 2FA requirement for certain forms. Rated

CVE-2026-26077 MEDIUM This Month POC

6.5 Feb 26

Unauthenticated attackers can submit forged webhook payloads to multiple email provider integrations in Discourse versio

CVE-2023-38706 MEDIUM This Month POC

6.5 Sep 15

Discourse is an open-source discussion platform. Rated medium severity (CVSS 6.5), this vulnerability is remotely exploi

CVE-2024-53991 MEDIUM This Month POC

5.9 Dec 19

Discourse is an open source platform for community discussion. Rated medium severity (CVSS 5.9), this vulnerability is r

CVE-2025-48877 CRITICAL Act Now

9.8 Jun 09

Discourse versions prior to 3.4.4 (stable), 3.5.0.beta5 (beta), and 3.5.0.beta6-dev (tests-passed) contain a critical vu

CVE-2023-47121 CRITICAL Act Now

9.8 Nov 10

Discourse is an open source platform for community discussion. Rated critical severity (CVSS 9.8), this vulnerability is

CVE-2022-39355 CRITICAL Act Now

9.8 Oct 26

Discourse Patreon enables syncronization between Discourse Groups and Patreon rewards. Rated critical severity (CVSS 9.8

Same weakness CWE-79 – Cross-site Scripting (XSS)

View all

CVE-2020-3580 MEDIUM POC

6.1

CVE-2013-7389 MEDIUM POC

4.3

CVE-2021-25299 MEDIUM POC

6.1

CVE-2014-2120 MEDIUM

6.1

CVE-2023-40000 HIGH POC

8.3

CVE-2016-8581 MEDIUM POC

6.1

CVE-2013-5223 MEDIUM POC

5.4

CVE-2025-52367 MEDIUM POC

5.4

Same technique XSS

View all

CVE-2017-9248 CRITICAL POC

9.8

CVE-2013-1710 CRITICAL POC

10.0

CVE-2024-52875 HIGH POC

8.8

References

Advisories & patches

ADVISORY https://vuldb.com/?id.351868 REF https://github.com/discourse/discourse/commit/44b84439df7e4424b2e7f216fd8fdd7dacff2227 REF https://github.com/discourse/discourse/commit/8ae7cb2414d6918d7fc45e1fda7ffbb32912a975 REF https://github.com/discourse/discourse/commit/ed70949f2c047196f33cfa94f2819df29c5d1e5f REF https://github.com/discourse/discourse/security/advisories/GHSA-95hc-42c6-wvvr

Search Externally

GitHub PoC

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