Stored and reflected XSS in SiYuan via SVG sanitizer bypass (CVE-2026-66394)

SiYuan's SVG sanitizer parses attacker-supplied SVG input using an HTML parser while the browser receives the output as image/svg+xml (XML). Because HTML and XML parsers treat elements such as desc, style, and noscript differently, script tags nested within those elements survive sanitization and execute in the application origin when the file is opened. The flaw is reachable both as a reflected vulnerability via GET /api/icon/getDynamicIcon and as a stored vulnerability via planted .svg assets, and no Content Security Policy is present to prevent script execution. Any authenticated user-Administrator, Editor, or Reader-can trigger either vector. Affected versions: - <= 3.7.2 We recommend updating to: v3.7.3. CVSS 9.3 · our assessment: act_now Reference: https://github.com/siyuan-note/siyuan/security/advisories/GHSA-99rq-75j6-5j9f Details: https://vuln.today/cve/CVE-2026-66394