CVE-2026-84803: Siyuan-Note Siyuan

Critical severity, CVSS 9.0. EPSS: 0.4% chance of exploitation in the next 30 days.

SiYuan before v3.8.2 contains a stored cross-site scripting vulnerability in asset serving due to an incomplete extension blocklist that misses script-capable file types. Attackers can upload files with extensions like .xht, .ehtml, .xsl, .xbl, or .rdf that resolve to executable media types and execute JavaScript to steal API tokens and compromise workspaces.

Affected products

• Siyuan-Note Siyuan: before 3.8.2 (fixed in 3.8.2)

Published 2026-09-02. Last modified 2026-09-02.