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.

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)

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.

Affected products

Siyuan-note Siyuan

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

References

disclosure@vulncheck.com (vendor-advisory)
disclosure@vulncheck.com (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.