SiYuan is a personal knowledge management system. Prior to version 3.6.2, the Siyuan kernel exposes an unauthenticated file-serving endpoint under `/appearance/*filepath.` Due to improper path sanitization, attackers can perform directory traversal and read arbitrary files accessible to the server process. Authentication checks explicitly exclude this endpoint, allowing exploitation without valid credentials. Version 3.6.2 fixes this issue.

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

## Summary

The Siyuan kernel exposes an unauthenticated file-serving endpoint under **/appearance/*filepath.** Due to improper path sanitization, attackers can perform directory traversal and read arbitrary files accessible to the server process.

Authentication checks explicitly exclude this endpoint, allowing exploitation without valid credentials.

## Details

Vulnerable Code Location

**File: kernel/server/serve.go**

``` sh siyuan.GET("/appearance/*filepath", func(c *gin.Context) { filePath := filepath.Join( appearancePath, strings.TrimPrefix(c.Request.URL.Path, "/appearance/") ) ... c.File(filePath) }) ```

**Technical Root Cause**

The handler constructs a filesystem path by joining a base directory (appearancePath) with user-controlled URL segments.

**Key issues:**

**1. Unsanitized User Input**

The path component extracted from the request is not validated or normalized to prevent traversal.

``` sh strings.TrimPrefix(c.Request.URL.Path, "/appearance/") ```

This preserves sequences such as:

``` sh ../ ..\ (Windows) ```

**2. Unsafe Path Joining**

**_filepath.Join()_** does not enforce directory confinement.

This escapes the intended directory.

**3. Direct File Serving**

The resolved path is served without verification:

``` sh c.File(filePath) ```

### Authentication Bypass (Unauthenticated Access)

Authentication middleware explicitly skips /appearance/ requests.

**File: session.go** ``` sh if strings.HasPrefix(c.Reques…