CVE-2026-31809: b3log siyuan Cross-site Scripting

Vulnerability summary

CVE-2026-31809 is a medium (CVSS 6.4) Cross-site Scripting vulnerability in b3log siyuan. EPSS estimates a 0.57% chance of exploitation in the next 30 days, higher than 46% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 10-03-2026
   PublishedVulnerability first disclosed.
2. 11-03-2026
   Last modifiedVulnerability information updated.

Description

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.

• CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.