Описание
9router: Missing Authorization and OS Command Injection
Unauthenticated RCE via /api/tunnel/tailscale-install
Affected: 9router (npm package) — current master (v0.4.39).
Summary
POST /api/tunnel/tailscale-install accepts a JSON body with a sudoPassword field and pipes it, followed by the body of https://tailscale.com/install.sh, into a child process spawned as sudo -S sh. The route is not present in the dashboard middleware matcher in src/proxy.js, so the request reaches the handler without invoking dashboardGuard.proxy(). In deployments where the Node process runs as root (Docker images derived from node:* without a USER directive, npm i -g 9router invoked as root, or systemd units without User=), the spawned sh runs as root and executes the attacker-supplied bytes.
Details
1. Middleware matcher (src/proxy.js:3-15)
Next.js invokes the middleware only for paths matching this list. Routes that are not listed — including the entire /api/tunnel/* family — do not invoke dashboardGuard.proxy(). No cookie, JWT, CLI token, or Host-header check is applied to them.
2. Route handler (src/app/api/tunnel/tailscale-install/route.js:18-67)
body.sudoPassword comes from the request body and is passed to installTailscale, which dispatches to installTailscaleLinux on Linux.
3. Linux installation routine (src/lib/tunnel/tailscale.js:304-341)
The byte stream sent to the stdin of the sudo -S sh child process is:
When the caller is already root, has NOPASSWD configured for the user, or has a recent sudo timestamp cache, sudo -S sh does not read stdin for a password — it execs sh directly. The new sh process inherits the stdin pipe and reads it line by line:
- The
sudoPasswordvalue from the request — interpreted as the first shell command. - The
install.shbody — interpreted as subsequent shell input.
Appending ; exit 0 to the sudoPassword value causes sh to exit before the legitimate install.sh body runs. The host executes only the request-supplied bytes, as the 9router process user.
Both "Docker container running as root" and "npm i -g 9router on a host with NOPASSWD sudo" reach this path.
PoC
The reproduction below is self-contained: build a representative target image (Node process running as root, with sudo and curl on PATH), start it, send one unauthenticated POST with curl, and read the file written by the payload.
Step 1 — build the target image
Step 2 — start the target
Step 3 — exploit (one unauthenticated POST)
Step 4 — verify
The trailing "Tailscale not installed" line is a consequence of ; exit 0 terminating sh before the legitimate install.sh body executed; the id > /tmp/pwned.txt write completed earlier in the same sh invocation. The POST carried no credentials, cookies, or prior state.
Impact
Type: Improper Access Control + OS Command Injection (CWE-862 + CWE-78).
Affected operators: 9router operators on Linux/macOS whose deployment matches one of the following configurations:
| Configuration | Example | Outcome |
|---|---|---|
| Node process runs as root | Custom Dockerfile without USER, systemd unit without User=, sudo npm i -g 9router && sudo 9router | Unauthenticated remote root RCE (primary case in this report) |
Node process runs as a normal user with NOPASSWD sudo | Developer laptop, CI runner, or single-tenant VPS where the operator's user has NOPASSWD: ALL | Unauthenticated remote RCE as the operator's user; root reachable via sudo from the foothold |
Node process runs as a normal user without NOPASSWD and no stored password | Hardened multi-user host | The spawn runs but sudo rejects the supplied value. No RCE; the request still triggers an outbound fetch from tailscale.com and the SSE error stream reveals platform information |
Пакеты
9router
< 0.4.44
0.4.44
Связанные уязвимости
9Router before 0.4.44 contains an OS command injection vulnerability in the unauthenticated POST /api/tunnel/tailscale-install endpoint (this route is not covered by the dashboard middleware matcher, so no authorization check is applied). The sudoPassword field from the request body is written to the stdin of a 'sudo -S sh' child process. When sudo does not prompt for a password (the process runs as root, NOPASSWD is configured, or a recent sudo timestamp cache exists), the sudoPassword value is interpreted by sh as a shell command, allowing a remote unauthenticated attacker to execute arbitrary OS commands. Exploitation evidence was first observed by the Shadowserver Foundation on 2026-07-04 (UTC).