Summary

npx claude-code-templates --studio launches "Claude Code Studio", an Express HTTP server (cli-tool/src/sandbox-server.js, default port 3444) that binds to all interfaces (0.0.0.0), sets Access-Control-Allow-Origin: *, and requires no authentication. Two POST endpoints pass attacker-controlled request-body fields into child_process.spawn(..., { shell: true }). Because shell: true makes Node join the argv array into a single sh -c string, the fields are parsed by the shell and metacharacters execute. Any unauthenticated attacker who can reach the port — a malicious web page the developer visits, or anyone on the same LAN — can execute arbitrary OS commands on the developer's machine.

Details

In cli-tool/src/sandbox-server.js:

• app.listen(PORT, ...) is called with no host argument, so the server listens on 0.0.0.0 / :: (reachable from the LAN, not just localhost).
• The CORS middleware sends Access-Control-Allow-Origin: * and answers the preflight OPTIONS for any origin, so a browser will deliver cross-origin POSTs to it.
• There is no authentication on any endpoint.

The vulnerable sinks:

1. POST /api/execute — the prompt body field flows into executeLocalTask():

   const child = spawn('claude', [finalPrompt], { /* ... */ shell: true });
   The only validation on prompt is a length check (>= 10 chars). With shell: true, finalPrompt is interpreted by the shell.
   

2. POST /api/install-agent — the agentName body field: const child = spawn('npx', ['claude-code-templates@latest', '--agent', agentName, '--yes'], { /* ... */ shell: true });

3. agentName is used unvalidated. (The same unsafe pattern is also reachable through /api/execute's agent field via checkAndInstallAgent().)

Root cause: spawn(cmd, argsArray, { shell: true }) does not keep argsArray as separate argv entries — Node builds cmd + ' ' + argsArray.join(' ') and runs it via sh -c, so every element is subject to shell parsing.

PoC

Victim

npx claude-code-templates --studio # server on 0.0.0.0:3444

Attacker (another LAN host, or a malicious web page fetch(), or locally)

curl -s -X POST http://127.0.0.1:3444/api/execute
-H 'Content-Type: application/json'
--data '{"prompt":"aaaaaaaaaa; touch /tmp/CCT_RCE_PROOF","mode":"local"}'

curl -s -X POST http://127.0.0.1:3444/api/install-agent
-H 'Content-Type: application/json'
--data '{"agentName":"x; touch /tmp/CCT_AGENT_PROOF #"}'

ls -la /tmp/CCT_RCE_PROOF /tmp/CCT_AGENT_PROOF # both created => injected commands ran The aaaaaaaaaa padding satisfies the 10-char minimum, then ; (or $(...), or backticks) starts the injected command. claude/npx do not even need to be installed — the injected segment runs regardless.

Confirmed at runtime on v1.28.13 (Node 22, Linux): both marker files were created, the server listened on *:3444, and an OPTIONS preflight from Origin: https://evil.example returned 200 with Access-Control-Allow-Origin: *.

Impact

Unauthenticated remote code execution (CWE-78) on any machine running --studio. Two reachability paths:

• Drive-by: a developer running --studio who visits an attacker-controlled web page — the page's cross-origin fetch() (Content-Type application/json) passes the wildcard CORS preflight and delivers the POST, achieving RCE with no other interaction.
• LAN: because the server binds 0.0.0.0, anyone on the same network (office, co-working space, public Wi-Fi) can hit port 3444 directly.

Impact is full compromise of the developer's user account (arbitrary command execution with the developer's privileges): source code, SSH keys, cloud credentials, and .env secrets.

Suggested fix

• Remove shell: true from all three spawns so arguments stay discrete argv entries (kills the injection).
• Validate agentName against a strict allowlist (^[A-Za-z0-9._/-]+$).
• Bind to loopback only (app.listen(PORT, '127.0.0.1', ...)).
• Replace the wildcard CORS with a same-origin allowlist and reject other origins.