diff --git a/src/shared/json-schema-defaults.test.ts b/src/shared/json-schema-defaults.test.ts
index 179c188a5680..9658cfc5343b 100644
--- a/src/shared/json-schema-defaults.test.ts
+++ b/src/shared/json-schema-defaults.test.ts
@@ -1,5 +1,9 @@
-import { describe, expect, it } from "vitest";
-import { findJsonSchemaShapeError, normalizeJsonSchemaForTypeBox } from "./json-schema-defaults.js";
+import { afterEach, describe, expect, it } from "vitest";
+import {
+  applyJsonSchemaDefaults,
+  findJsonSchemaShapeError,
+  normalizeJsonSchemaForTypeBox,
+} from "./json-schema-defaults.js";
 
 describe("normalizeJsonSchemaForTypeBox", () => {
   it("combines pattern properties that collide after unicode repair", () => {
@@ -47,3 +51,45 @@ describe("normalizeJsonSchemaForTypeBox", () => {
     ).toBeUndefined();
   });
 });
+
+describe("applyJsonSchemaDefaults prototype safety", () => {
+  const readPollution = () => (Object.prototype as Record<string, unknown>).polluted;
+
+  afterEach(() => {
+    delete (Object.prototype as Record<string, unknown>).polluted;
+  });
+
+  it("does not pollute Object.prototype through a __proto__ property schema", () => {
+    const schema = JSON.parse(
+      '{"type":"object","properties":{"__proto__":{"type":"object","properties":{"polluted":{"default":"yes"}}}}}',
+    );
+
+    const result = applyJsonSchemaDefaults(schema, {});
+
+    expect(readPollution()).toBeUndefined();
+    expect(({} as Record<string, unknown>).polluted).toBeUndefined();
+    expect(Object.hasOwn(result, "polluted")).toBe(false);
+  });
+
+  it("does not pollute Object.prototype through a __proto__ pattern property schema", () => {
+    const schema = JSON.parse(
+      '{"type":"object","patternProperties":{".*":{"type":"object","properties":{"polluted":{"default":"yes"}}}}}',
+    );
+    const value = JSON.parse('{"__proto__":{}}');
+
+    applyJsonSchemaDefaults(schema, value);
+
+    expect(readPollution()).toBeUndefined();
+  });
+
+  it("does not pollute Object.prototype through a __proto__ additional property schema", () => {
+    const schema = JSON.parse(
+      '{"type":"object","additionalProperties":{"type":"object","properties":{"polluted":{"default":"yes"}}}}',
+    );
+    const value = JSON.parse('{"__proto__":{}}');
+
+    applyJsonSchemaDefaults(schema, value);
+
+    expect(readPollution()).toBeUndefined();
+  });
+});
diff --git a/src/shared/json-schema-defaults.ts b/src/shared/json-schema-defaults.ts
index 20e57cb70a5c..5a30c5cd7ab8 100644
--- a/src/shared/json-schema-defaults.ts
+++ b/src/shared/json-schema-defaults.ts
@@ -1,6 +1,7 @@
 import { isRecord } from "@openclaw/normalization-core/record-coerce";
 // JSON schema default helpers fill object values from TypeBox schema defaults.
 import { Compile } from "typebox/compile";
+import { isBlockedObjectKey } from "../infra/prototype-keys.js";
 import type { JsonSchemaObject } from "./json-schema.types.js";
 
 type JsonSchemaValue = JsonSchemaObject | boolean;
@@ -926,6 +927,9 @@ function applyObjectPropertyDefaults(
 ): Record<string, unknown> {
   const properties = isRecord(schema.properties) ? schema.properties : {};
   for (const [key, propertySchema] of Object.entries(properties)) {
+    if (isBlockedObjectKey(key)) {
+      continue;
+    }
     const currentValue = value[key];
     const defaultedValue = applySchemaDefaults(
       propertySchema as JsonSchemaValue,
@@ -951,7 +955,7 @@ function applyObjectPropertyDefaults(
         continue;
       }
       for (const key of Object.keys(value)) {
-        if (!regex.test(key)) {
+        if (isBlockedObjectKey(key) || !regex.test(key)) {
           continue;
         }
         patternMatchedKeys.add(key);
@@ -969,7 +973,11 @@ function applyObjectPropertyDefaults(
   if (isRecord(schema.additionalProperties)) {
     const additionalSchema = schema.additionalProperties as JsonSchemaValue;
     for (const key of Object.keys(value)) {
-      if (Object.hasOwn(properties, key) || patternMatchedKeys.has(key)) {
+      if (
+        isBlockedObjectKey(key) ||
+        Object.hasOwn(properties, key) ||
+        patternMatchedKeys.has(key)
+      ) {
         continue;
       }
       value[key] = applySchemaDefaults(