CVE-2026-105798: XSS (CVSS 8.7)

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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CVSS v3.1 Score

8.7

HIGH

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N

EPSS — Exploit Prediction

0.0047

Probability of exploitation

0.38%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-79 Cross-site Scripting (XSS)

References

Other 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

Frequently Asked Questions

What is CVE-2026-105798? +

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. It has a CVSS v3.1 base score of 8.7 (HIGH).

How severe is CVE-2026-105798? +

CVE-2026-105798 has a CVSS v3.1 score of 8.7 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0047, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-105798? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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