CVE-2026-66394

Severity CVSS v4.0:

CRITICAL

Type:

CWE-79 Cross-Site Scripting (XSS)

Publication date:

27/07/2026

Last modified:

27/07/2026

Description

SiYuan before v3.7.3 contains stored and reflected cross-site scripting vulnerabilities in SVG sanitization that allows authenticated attackers to execute scripts by bypassing the HTML parser-based cleaner. Attackers can hide script tags within desc, style, or noscript elements which the HTML parser treats as raw text but browsers interpret as executable SVG content when served as image/svg+xml, enabling script execution in the application origin.

Impact

Vector 4.0

CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:H/VI:H/VA:N/SC:H/SI:H/SA:N CVSS v4.0 Severity and Metrics:

Base Score: 9.30 CRITICAL
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:H/VI:H/VA:N/SC:H/SI:H/SA:N

Attack Vector (AV): Network
Attack Complexity (AC): Low
Attack Requirements (AT): None
Privileges Required (PR): Low
User Interaction (UI): Passsive
Confidentiality (VC): High
Integrity (VI): High
Availability (VA): None
Confidentiality (SC): High
Integrity (SI): High
Availability (SA): None

Base Score 4.0

9.30

Severity 4.0

CRITICAL

Vector 3.x

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N CVSS v3.1 Severity and Metrics:

Base Score: 8.70 HIGH
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N

Attack Vector (AV): Network
Attack Complexity (AC): Low
Privileges Required (PR): Low
User Interaction (UI): Required
Scope (S): Changed
Confidentiality (C): High
Integrity (I): High
Availability (A): None

Base Score 3.x

8.70

Severity 3.x

HIGH

CVE-2026-66394

Description

Impact

References to Advisories, Solutions, and Tools