CVE-2026-84803

SiYuan before v3.8.2 Stored XSS via incomplete asset blocklist

8.6 High

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.

Attack profile

How easy it is to exploit

Attack vector: Network
Complexity: Low
Privileges needed: Low
User interaction: Passive

What an attacker can affect

Confidentiality: High
Integrity: High
Availability: High

Exploit likelihood

0.43%Up 0.2 points since Sep 3, 2026

What each source reports

CVE List Score used8.6

SiYuan before v3.8.2 Stored XSS via incomplete asset blocklist

Record: CVE-2026-84803
CVSS 4.0: 8.6 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
CVSS 3.1: 9.0 CriticalCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H
Weakness: CWE-79
Updated: 2026-11-02

EUVDEUVD-2026-699158.6

Record: EUVD-2026-69915
CVSS 4.0: 8.6 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
Updated: 2026-11-02

GitHub AdvisoriesGHSA-73j8-px8h-3w2h8.6

SiYuan before v3.8.2 contains a stored cross-site scripting vulnerability in asset serving due to...

Record: GHSA-73j8-px8h-3w2h
CVSS 4.0: 8.6 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CVSS 3.1: 9.0 CriticalCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H
Weakness: CWE-79
Updated: 2026-11-02

NVD8.6

Record: CVE-2026-84803
CVSS 4.0: 8.6 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CVSS 3.1: 9.0 CriticalCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H
Weakness: CWE-79
Updated: 2026-11-02

OSV8.6

SiYuan before v3.8.2 Stored XSS via incomplete asset blocklist

Record: CVE-2026-84803
CVSS 4.0: 8.6 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
Weakness: CWE-79
Updated: 2026-11-02

Affected products

siyuan-note siyuan

History

History
Recorded	Changed	Sources
Nov 2, 2026	first indexed	CVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-84803 is a high vulnerability (CVSS 8.6) in Siyuan-note Siyuan, published September 2, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.43%, the 37th percentile. No source names a fixed version.