security(gateway): block prototype traversal in hook template paths

src/gateway/hooks-mapping.test.ts

@@ -372,4 +372,69 @@ describe("hooks mapping", () => {
     });
     expect(result?.ok).toBe(false);
   });
+
+  describe("prototype pollution protection", () => {
+    it("blocks __proto__ traversal in webhook payload", async () => {
+      const mappings = resolveHookMappings({
+        mappings: [
+          createGmailAgentMapping({
+            id: "proto-test",
+            messageTemplate: "value: {{__proto__}}",
+          }),
+        ],
+      });
+      const result = await applyHookMappings(mappings, {
+        payload: { __proto__: { polluted: true } } as Record<string, unknown>,
+        headers: {},
+        url: baseUrl,
+        path: "gmail",
+      });
+      expect(result?.ok).toBe(true);
+      if (result?.ok && result.action && result.action.kind === "agent") {
+        expect(result.action.message).toBe("value: ");
+      }
+    });
+
+    it("blocks constructor traversal in webhook payload", async () => {
+      const mappings = resolveHookMappings({
+        mappings: [
+          createGmailAgentMapping({
+            id: "constructor-test",
+            messageTemplate: "type: {{constructor.name}}",
+          }),
+        ],
+      });
+      const result = await applyHookMappings(mappings, {
+        payload: { constructor: { name: "INJECTED" } } as Record<string, unknown>,
+        headers: {},
+        url: baseUrl,
+        path: "gmail",
+      });
+      expect(result?.ok).toBe(true);
+      if (result?.ok && result.action && result.action.kind === "agent") {
+        expect(result.action.message).toBe("type: ");
+      }
+    });
+
+    it("blocks prototype traversal in webhook payload", async () => {
+      const mappings = resolveHookMappings({
+        mappings: [
+          createGmailAgentMapping({
+            id: "prototype-test",
+            messageTemplate: "val: {{prototype}}",
+          }),
+        ],
+      });
+      const result = await applyHookMappings(mappings, {
+        payload: { prototype: "leaked" } as Record<string, unknown>,
+        headers: {},
+        url: baseUrl,
+        path: "gmail",
+      });
+      expect(result?.ok).toBe(true);
+      if (result?.ok && result.action && result.action.kind === "agent") {
+        expect(result.action.message).toBe("val: ");
+      }
+    });
+  });
 });

src/gateway/hooks-mapping.ts

@@ -80,6 +80,8 @@ const hookPresetMappings: Record<string, HookMappingConfig[]> = {
 
 const transformCache = new Map<string, HookTransformFn>();
 
+const BLOCKED_PATH_KEYS = new Set(["__proto__", "prototype", "constructor"]);
+
 type HookTransformResult = Partial<{
   kind: HookAction["kind"];
   text: string;
@@ -465,6 +467,9 @@ function getByPath(input: Record<string, unknown>, pathExpr: string): unknown {
       current = current[part] as unknown;
       continue;
     }
+    if (BLOCKED_PATH_KEYS.has(part)) {
+      return undefined;
+    }
     if (typeof current !== "object") {
       return undefined;
     }