EUVD-2026-275548

fkie_cve-2026-31809

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.

GHSA-pmc9-f5qr-2pcr — SiYuan has a SVG Sanitizer Bypass via Whitespace in `javascript:` URI — Unauthenticated XSS

Affected: Go: github.com/siyuan-note/siyuan/kernel

# SVG Sanitizer Bypass via Whitespace in `javascript:` URI — Unauthenticated XSS

## Summary

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), [distinct from the `<animate>` element bypass](https://github.com/siyuan-note/siyuan/security/advisories/GHSA-5hc8-qmg8-pw27).

## Affected Component

- **File:** `kernel/util/misc.go` - **Function:** `SanitizeSVG()` (lines 234-319) - **Specific check:** Line 271 — `strings.HasPrefix(val, "javascript:")` - **Endpoint:** `GET /api/icon/getDynamicIcon?type=8&content=...` (unauthenticated) - **Version:** SiYuan <= 3.5.9

## Root Cause

The sanitizer uses Go's `html.Parse` which decodes HTML entities in attribute values. When the input contains `java	script:alert(1)`, the parser decodes `	` to a literal tab character (U+0009). The sanitizer then checks:

```go val := strings.TrimSpace(strings.ToLower(a.Val)) // val is now "java\tscript:alert(1)"

if strings.HasPref…

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EUVD-2026-275548

fkie_cve-2026-31809

GHSA-pmc9-f5qr-2pcr — SiYuan has a SVG Sanitizer Bypass via Whitespace in `javascript:` URI — Unauthenticated XSS