CVE-2026-66394

SiYuan before v3.7.3 Stored and Reflected XSS via SVG Sanitizer Bypass

HIGH
8.7
CVSS Score
Published: July 27, 2026 at 03:43 PM UTC
Updated: October 24, 2026 at 01:10 PM UTC
2 products affected across 2 vendorsSiyuanSiyuan

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Severity
HIGH8.7
Exploit prediction
EPSS 0.3%
SSVC
PoC

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

v < 3.7.3
Affected range stops below 3.7.3, so it looks safe — our inference, not a vendor statement
0 ≤ v < 3.7.30
Vendor states this is fixed in 3.7.3 (unaffected)

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

SSVC — Action Prioritization

SSVCPoCNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

8.7HIGHVulnCheck
Attack Vector
NETWORK
Complexity
LOW
Privileges
LOW
User Interaction
REQUIRED
Scope
CHANGED
Confidentiality
HIGH
Integrity
HIGH
Availability
NONE
Vector?

Quick Info

StatusDEFERRED
CWE
CWE-79

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