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CVE-2026-31809— SiYuan has a SVG Sanitizer Bypass via Whitespace in `javascript:` URI — Unauthenticated XSS

Quick assessment

Affected
siyuan-note siyuan
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

SiYuan是SiYuan开源的一个隐私至上的个人知识管理系统。 SiYuan 3.5.10之前版本存在跨站脚本漏洞，该漏洞源于SVG清理器对href属性中javascript:前缀的检查可被绕过，可能导致反射型跨站脚本攻击。

AI Predicted 6.1 Difficulty: Moderate EPSS 0.57% · P46

Public Exploits 1

Nuclei · 1 CVE-2026-31809.yaml [template]
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I. Basic Information for CVE-2026-31809

Vulnerability Information
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Vulnerability Title
SiYuan has a SVG Sanitizer Bypass via Whitespace in `javascript:` URI — Unauthenticated XSS
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
在Web页面生成时对输入的转义处理不恰当(跨站脚本)
Source: CVE Program / CVE List V5
Vulnerability Title
SiYuan 跨站脚本漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
SiYuan是SiYuan开源的一个隐私至上的个人知识管理系统。 SiYuan 3.5.10之前版本存在跨站脚本漏洞，该漏洞源于SVG清理器对href属性中javascript:前缀的检查可被绕过，可能导致反射型跨站脚本攻击。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
siyuan-note siyuan < 3.5.10 -

II. Public POCs for CVE-2026-31809

# POC Description Source Link Shenlong Link
1 SiYuan v3.5.10 contains a reflected XSS caused by improper sanitization of javascript: href attributes allowing ASCII control characters to bypass prefix checks in SVG sanitizer, letting unauthenticated attackers execute JavaScript via /api/icon/getDynamicIcon. https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2026/CVE-2026-31809.yaml POC Details
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III. Intelligence Information for CVE-2026-31809

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Vendor Advisories for CVE-2026-31809 (1)

IV. Related Vulnerabilities

Same product: siyuan
Same vendor: siyuan-note
Same weakness: CWE-79

V. Comments for CVE-2026-31809

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