CVE-2026-105798
Received Received - Intake

Stored XSS in SimpleChat via Filename in Group Document Upload

Publication date: 2026-10-06

Last updated on: 2026-10-06

Assigner: GitHub, Inc.

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.

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Meta Information

Published
2026-10-06
Last Modified
2026-10-06
Generated
2026-10-06
AI Q&A
2026-10-06
EPSS Evaluated
N/A
NVD
CVE-2026-105798
EUVD
EUVD-2026-93427

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
microsoft simplechat < 0.261.029

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-79 The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.

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Executive Summary

SimpleChat before 0.261.029 has a stored cross-site scripting (XSS) flaw in the group document upload feature. An attacker with group Owner, Admin, or DocumentManager privileges can upload a filename containing malicious JavaScript code. When another user views the Share dialog, the filename is rendered in an event handler without proper escaping, allowing the script to execute in the SimpleChat origin and access the victim's session data and actions.

Detection Guidance

This vulnerability involves improper handling of filenames in the SimpleChat application, leading to stored XSS via group document uploads. To detect it, inspect SimpleChat server logs for suspicious filename patterns containing HTML or JavaScript code. Check if group_workspaces.html renders filenames without proper escaping. Verify if users report unexpected script execution when sharing documents.

Impact Analysis

If you are a SimpleChat user in a group where an attacker has elevated privileges, clicking Share on a malicious document could execute arbitrary JavaScript in your browser within the SimpleChat application. This could lead to theft of session cookies, unauthorized actions on your behalf, or exposure of sensitive data visible in your account.

Compliance Impact

This vulnerability could lead to unauthorized access to personal or health data, violating GDPR's data protection principles and HIPAA's security requirements for protected health information. A breach may result in legal penalties, reputational damage, and loss of compliance certifications.

Mitigation Strategies

Upgrade SimpleChat to version 0.261.029 or later to patch the vulnerability. Temporarily restrict document uploads to trusted users until patched. Monitor for unusual activity in group workspaces. Implement input validation for filenames to reject or sanitize special characters.

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0/70

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