fix: protect MCP config credentials

CHANGELOG.md

@@ -12,6 +12,7 @@
 
 ### Fixed
 
+- Restrict the generated MCP configuration to owner read/write permissions on POSIX systems before persisting authentication credentials.
 - Include source-backed JSON fact documents in `!storage` profile file counts.
 - Refuse to save pending Discord messages through symbolic-link destinations.
 - Protect legacy and source-backed user/server memory reads and writes from symbolic links, junctions, and path swaps.

src/mcp/http.ts

@@ -109,7 +109,17 @@ export function writeMcpConfig() {
     const config = {
         mcpServers,
     };
-    fs.writeFileSync(MCP_CONFIG_PATH, JSON.stringify(config, null, 2), "utf-8");
+    const fileDescriptor = fs.openSync(MCP_CONFIG_PATH, "w", 0o600);
+    try {
+        fs.fchmodSync(fileDescriptor, 0o600);
+        fs.writeFileSync(
+            fileDescriptor,
+            JSON.stringify(config, null, 2),
+            "utf-8",
+        );
+    } finally {
+        fs.closeSync(fileDescriptor);
+    }
     console.error(`[MCP] Config written to ${MCP_CONFIG_PATH}`);
 }
 

tests/mcpHttp.test.mjs

@@ -105,8 +105,11 @@ test("generated MCP config includes authenticated Morpheus HTTP transport", () =
     );
     const moduleUrl = new URL("../build/mcp/http.js", import.meta.url).href;
     const apiKey = "test-morpheus-api-key";
+    const configPath = path.join(workingDir, ".mcp-config.json");
 
     try {
+        fs.writeFileSync(configPath, "stale config", { mode: 0o666 });
+        fs.chmodSync(configPath, 0o666);
         const result = spawnSync(
             process.execPath,
             [
@@ -128,16 +131,17 @@ test("generated MCP config includes authenticated Morpheus HTTP transport", () =
 
         assert.equal(result.status, 0, result.stderr);
         assert.doesNotMatch(result.stderr, new RegExp(apiKey));
-        const config = JSON.parse(
-            fs.readFileSync(path.join(workingDir, ".mcp-config.json"), "utf8"),
-        );
+        const config = JSON.parse(fs.readFileSync(configPath, "utf8"));
         assert.deepEqual(config.mcpServers.morpheus, {
             type: "http",
             url: "http://morpheus_bot_prod:5268/api/mcp",
             headers: {
                 Authorization: `Bearer ${apiKey}`,
             },
         });
+        if (process.platform !== "win32") {
+            assert.equal(fs.statSync(configPath).mode & 0o777, 0o600);
+        }
     } finally {
         fs.rmSync(workingDir, { recursive: true, force: true });
     }