Discourse
CVE-2026-33395
MEDIUM
Vulnerability Assessment
| Weakness |
CWE
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. |
| Impact | Attackers can steal session cookies, redirect users to malicious sites, deface content, or perform actions on behalf of authenticated users. With a CVSS score of 4.4 (MEDIUM), this represents a moderate risk. |
| 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. |
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Alert meAnalysisAIv1 – Mar 19, 2026
Authenticated users can inject persistent JavaScript through malicious DOT graph definitions in the discourse-graphviz plugin on Discourse versions prior to 2026.3.0-latest.1, 2026.2.1, and 2026.1.2, enabling stored XSS attacks when Content Security Policy is disabled. Affected instances should upgrade to patched versions, disable the plugin, or enforce a CSP as a temporary mitigation, as no patch is currently available for all deployment scenarios.
Earlier versions of this analysis (1)
RemediationAI
Encode all user-supplied output contextually (HTML, JS, URL). Implement Content Security Policy (CSP) headers. Use HTTPOnly and Secure cookie flags.
Affects your stack
Find out whether the stacks and servers you run are on an affected version.
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
AV:N/AC:H/PR:L/UI:R/S:C/C:L/I:L/A:N
Primary rating from GitHub Advisory · only source for this CVE.
CVSS VectorGitHub Advisory
DescriptionGitHub Advisory
Discourse is an open-source discussion platform. Prior to versions 2026.3.0-latest.1, 2026.2.1, and 2026.1.2, the discourse-graphviz plugin contains a stored cross-site scripting (XSS) vulnerability that allows authenticated users to inject malicious JavaScript code through DOT graph definitions. For instances with CSP disabled only. Versions 2026.3.0-latest.1, 2026.2.1, and 2026.1.2 contain a patch. As a workaround, disable the graphviz plugin, upgrade to a patched version, or enable a content security policy.
Executive ViewAI
Organizations using Discourse should be aware of moderate risk from CVE-2026-33395, a cross-site scripting vulnerability rated CVSS 4.4. Attackers could inject scripts to steal sessions or perform actions as authenticated users. Organizations should apply vendor updates when available and monitor for exploitation.
Apply vendor patch. If patching is delayed: implement CSP headers, enable HttpOnly cookies, deploy WAF XSS rules.
Threat Intelligence Overview
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.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Cross-Site Scripting occurs when an application accepts untrusted data and sends it to a web browser without proper validation or encoding.
Affected Products (CPE)GitHub Advisory
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Exploit-DB