CVE-2026-84803: SiYuan before v3.8.2 Stored XSS via incomplete asset blocklist

Severity: critical (CVSS 9.0 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-09-02 · updated 2026-09-02
Weakness: CWE-79

Description

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

How to fix

Upgrade to a fixed version: siyuan-note siyuan 3.8.2. Check the vendor advisory for mitigations.

References

https://github.com/siyuan-note/siyuan/security/advisories/GHSA-7h8j-qw37-w46g
https://www.vulncheck.com/advisories/siyuan-before-3.8.2-stored-xss-via-incomplete-asset-blocklist
https://github.com/siyuan-note/siyuan/security/advisories/GHSA-7h8j-qw37-w46g

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