XSS in Siyuan-Note Siyuan
CVE-2026-84803
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.
Vulnerability class: XSS (Cross-Site Scripting)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 9.0 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.004 (35.6th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 36th percentile — 35.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.004 · change: +0.002
Affected products
Weakness classification (CWE)
References
- github.com/siyuan-note/siyuan/security/advisories/GHSA-7h8j-qw37-w46g (vendor-advisory)
- www.vulncheck.com/advisories/siyuan-before-3.8.2-stored-xss-via-incomplete-asse… (third-party-advisory)
Frequently asked questions
- What is CVE-2026-84803?
- CVE-2026-84803 is a critical-severity vulnerability in Siyuan-Note Siyuan, classified under Cross-site Scripting. CVSS score: 9.0/10. Published 2026-09-02.
- How severe is CVE-2026-84803?
- Critical severity. CVSS v3 base score is 9.0 out of 10.