🛡️ Sentinel: [CRITICAL] Fix fail-open file system access

.jules/sentinel.md

@@ -0,0 +1,6 @@
+# Sentinel Journal
+
+## 2026-01-20 - Default File System Exposure
+**Vulnerability:** The MCP server defaulted to allowing access to the entire file system (path traversal) when no `--allowed-workspace` arguments were provided.
+**Learning:** "Fail open" defaults are dangerous, especially for tools exposed to LLMs which might explore the system. The developers likely intended this for ease of use but underestimated the risk.
+**Prevention:** Always implement "fail closed" security. If configuration is missing, default to the most restrictive safe option (cwd) or deny access completely, rather than allowing everything.

src/index.ts

@@ -37,6 +37,15 @@ function parseArgs(args: string[]): { allowedWorkspaces: string[] } {
 
 async function main() {
   const { allowedWorkspaces } = parseArgs(process.argv.slice(2));
+
+  // If no allowed workspaces are specified, default to the current working directory
+  if (allowedWorkspaces.length === 0) {
+    const cwd = process.cwd();
+    console.error(`⚠️ No allowed workspaces specified. Defaulting to current working directory: ${cwd}`);
+    console.error('To allow other directories, use --allowed-workspace <path>');
+    allowedWorkspaces.push(cwd);
+  }
+
   const server = new CodeSearchMCPServer({ allowedWorkspaces });
   await server.start();
 }

src/utils/workspace-path.ts

@@ -53,9 +53,11 @@ export function validateAllowedPath(
 ): string {
   const normalized = path.resolve(requestedPath);
 
-  // If no allowed workspaces are configured, allow all paths
+  // If no allowed workspaces are configured, deny all access
   if (allowedWorkspaces.length === 0) {
-    return normalized;
+    throw new Error(
+      `Access denied: No allowed workspaces configured. Access to ${normalized} is denied.`
+    );
   }
 
   const isAllowed = allowedWorkspaces.some(allowed => {

tests/unit/error-handling.test.ts

@@ -104,9 +104,10 @@ describe('Error Handling and Edge Cases', () => {
       ).toThrow(/Access denied/);
     });
 
-    it('should allow any path when no workspaces are configured', () => {
-      const result = validateAllowedPath('/any/path', []);
-      expect(result).toBeDefined();
+    it('should deny any path when no workspaces are configured', () => {
+      expect(() =>
+        validateAllowedPath('/any/path', [])
+      ).toThrow(/Access denied/);
     });
 
     it('should allow exact match of allowed workspace', () => {

tests/unit/workspace-path-security.test.ts

@@ -0,0 +1,26 @@
+
+import { describe, it, expect } from '@jest/globals';
+import { validateAllowedPath } from '../../src/utils/workspace-path.js';
+import path from 'path';
+
+describe('Workspace Path Security', () => {
+  it('should DENY access when allowedWorkspaces is empty', () => {
+    // Secure behavior: empty array means allow nothing
+    expect(() => {
+      validateAllowedPath('/etc/passwd', []);
+    }).toThrow(/Access denied/);
+  });
+
+  it('should ALLOW access to explicitly allowed workspace', () => {
+    const cwd = process.cwd();
+    const result = validateAllowedPath(cwd, [cwd]);
+    expect(result).toBe(cwd);
+  });
+
+  it('should DENY access to path outside allowed workspace', () => {
+    const cwd = process.cwd();
+    expect(() => {
+        validateAllowedPath('/etc/passwd', [cwd]);
+    }).toThrow(/Access denied/);
+  });
+});