CVE-2026-105798: CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') in microsoft simplechat
Description
SimpleChat is a secure AI conversation application with personal and group workspaces for document-grounded interactions. Prior to 0.261.029, POST /api/group_documents/upload stores an attacker-controlled group document filename that group_workspaces.html later interpolates into inline Share event handlers. The escapeGroupHtml function leaves apostrophes unchanged, while escapeHtml produces an HTML entity that the browser decodes before JavaScript evaluation, so either path permits the filename to terminate the handler string. An authenticated group Owner, Admin, or DocumentManager can persist script that executes in the SimpleChat origin when another group member clicks Share, allowing access to victim-visible data and actions with the victim session. This issue is fixed in version 0.261.029.
CVSS v3.1
Score 8.7high
Affected software
microsoft
simplechat
pkg:github/microsoft/simplechatRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
Microsoft SimpleChat before version 0.261.029 contains a CWE-79 XSS vulnerability in the POST /api/group_documents/upload endpoint. The issue stems from the escapeGroupHtml function failing to escape apostrophes in group document filenames, which are interpolated into inline Share event handlers in group_workspaces.html. This improper input neutralization allows authenticated users with certain roles to persistently inject scripts that execute in the SimpleChat origin when other group members click Share, potentially exposing victim-visible data and enabling actions with the victim's session privileges. The vulnerability has a CVSS 3.1 score of 8.7, indicating high severity, and is fixed in version 0.261.029.
Potential Impact
An attacker with authenticated group Owner, Admin, or DocumentManager privileges can inject persistent cross-site scripting payloads via group document filenames. These scripts execute in the context of other group members' browsers when they click the Share button, leading to potential exposure of sensitive data and unauthorized actions performed with the victim's session. This compromises confidentiality and integrity but does not affect availability.
Mitigation Recommendations
Upgrade Microsoft SimpleChat to version 0.261.029 or later, where this vulnerability is fixed. No other mitigation is required as the fix addresses the improper input neutralization.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-10-05T20:37:19.364Z
- Cvss Version
- 3.1
- State
- PUBLISHED
Threat ID: 6ac506e32cdf04f656b9a062
Added to database: 10/06/2026, 14:34:11 UTC
Last enriched: 10/06/2026, 14:48:15 UTC
Last updated: 10/06/2026, 18:57:28 UTC
Views: 14
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