CVE-2026-31809
MEDIUM
GHSA-pmc9-f5qr-2pcr
CVSS Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Lifecycle Timeline
4Description
SiYuan is a personal knowledge management system. Prior to 3.5.10, SiYuan's SVG sanitizer (SanitizeSVG) checks href attributes for the javascript: prefix using strings.HasPrefix(). However, inserting ASCII tab (	), newline ( ), or carriage return ( ) characters inside the javascript: string bypasses this prefix check. Browsers strip these characters per the WHATWG URL specification before parsing the URL scheme, so the JavaScript still executes. This allows an attacker to inject executable JavaScript into the unauthenticated /api/icon/getDynamicIcon endpoint, creating a reflected XSS. This is a second bypass of the fix for CVE-2026-29183 (fixed in v3.5.9). This vulnerability is fixed in 3.5.10.
Analysis
SiYuan's SVG sanitizer fails to properly filter malicious href attributes when whitespace characters are inserted into javascript: URLs, allowing reflected cross-site scripting on the unauthenticated /api/icon/getDynamicIcon endpoint. Public exploit code exists for this vulnerability, which bypasses the previous fix for CVE-2026-29183. …
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Remediation
Within 30 days: Identify affected systems and apply vendor patches as part of regular patch cycle. Verify Content-Security-Policy and output encoding.
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External POC / Exploit Code
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