### 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()`: ```js 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 }); 2. 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.

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