GHSA-jxh8-jh77-xh6g

## Summary The validator-mode sandbox executor (`src/gep/validator/sandboxExecutor.js`) places `npm` and `npx` in its hard executable allowlist. Because `npm install <pkg>` and `npx -y -p <pkg> <bin>` execute arbitrary code by design (preinstall/install/postinstall lifecycle scripts and remote-package bin entries), and because validator nodes consume `validation_commands` strings from unsigned Hub responses with no per-response signature check, an attacker who controls or MITMs the Hub achieves automatic remote code execution on every validator node within one daemon poll (default 60s). ## Details End-to-end chain: 1. `src/gep/validator/index.js:71-87` — `fetchValidationTasks()` POSTs to `<hub>/a2a/fetch` and reads `validation_tasks` from the JSON response. The outbound request is signed via `buildHubHeaders()`, but the Hub's response is parsed directly with `await res.json()` and no signature is verified on `data.payload`. 2. `src/gep/validator/index.js:98-108` — `validateOneTask()` extracts `task.validation_commands` (an array of attacker-controlled strings) and passes it straight to `runInSandbox(commands, {})`. No call to `policyCheck.isValidationCommandAllowed()` happens on this path. The author's own comment at `sandboxExecutor.js:41-42` acknowledges this gap: *"This closes the gap where validation_commands go straight from Hub to runInSandbox without passing through policyCheck.isValidationCommandAllowed()."* 3. `src/gep/validator/sandboxExecutor.js:172-218` — `runSingleCommand` calls `parseCommand(cmd)`, then checks `ALLOWED_EXECUTABLES.has(parsed.executable)`: ```js // sandboxExecutor.js:35 const ALLOWED_EXECUTABLES = new Set(['node', 'npm', 'npx']); ``` `parseCommand` only rejects shell metacharacters (`| & ; > < \` $`) and unbalanced quotes. A string like `npm install /tmp/evil-pkg --no-audit --no-fund` contains none of those and parses cleanly into `{ executable: 'npm', args: [...] }`. 4. `sandboxExecutor.js:54-66` — `assertNodeCo