CVE-2026-100639 SiYuan - Stored XSS

SiYuan v3.8.3 contains a stored XSS caused by improper HTML-escaping of the data-subtype attribute in gutter-button markup from pasted Markdown with Kramdown IAL, letting attackers execute JavaScript with Node.js privileges in the Electron app, exploit requires victim to paste crafted Markdown and focus the gutter control.

CVSS base score 8.8 /10
High
CISA KEV
Not listed
Public exploit
None known
Authentication
Not required
EPSS
0.47% chance of exploitation in 30 days
View the NVD record ↗

Details

Type
Stored XSS
Impact
Remote Code Execution
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Published
26 September 2026
Updated
15 October 2026
Weakness
CWE-79

Vendor fix

Update to version 3.8.4 or later.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

References

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