What’s Vulnerable › Vulnerabilities

CVE-2026-105798: SimpleChat: Stored XSS via group document filename in inline onclick handler

• Severity: high (CVSS 8.7 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-06 · updated 2026-10-06
• Weakness: CWE-79

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.

Affected products

• microsoft simplechat: before 0.261.029

References

• https://github.com/microsoft/simplechat/commit/537a259eb048b8f6d1c94193fa0c9683ab0bace9
• https://github.com/microsoft/simplechat/security/advisories/GHSA-qwcw-r653-j8c6
• https://github.com/microsoft/simplechat/security/advisories/GHSA-qwcw-r653-j8c6

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