diff --git a/CHANGELOG.md b/CHANGELOG.md
index cfc0fcc2eb3..2f0d5b740c7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,6 +17,7 @@ Docs: https://docs.openclaw.ai
 ### Fixes
 
 - Chat/UI: strip inline reply/audio directive tags (`[[reply_to_current]]`, `[[reply_to:<id>]]`, `[[audio_as_voice]]`) from displayed chat history, live chat event output, and session preview snippets so control tags no longer leak into user-visible surfaces.
+- Security/Config: block prototype-key traversal during config merge patch and legacy migration merge helpers (`__proto__`, `constructor`, `prototype`) to prevent prototype pollution during config mutation flows. (#22968) Thanks @Clawborn.
 - Security/Shell env: validate login-shell executable paths for shell-env fallback (`/etc/shells` + trusted prefixes) and block `SHELL` in dangerous env override policy paths so untrusted shell-path injection falls back safely to `/bin/sh`. Thanks @athuljayaram for reporting.
 - Security/Config: make parsed chat allowlist checks fail closed when `allowFrom` is empty, restoring expected DM/pairing gating.
 - Security/Exec: in non-default setups that manually add `sort` to `tools.exec.safeBins`, block `sort --compress-program` so allowlist-mode safe-bin checks cannot bypass approval. Thanks @tdjackey for reporting.
diff --git a/src/config/legacy.shared.test.ts b/src/config/legacy.shared.test.ts
new file mode 100644
index 00000000000..3a6ff256487
--- /dev/null
+++ b/src/config/legacy.shared.test.ts
@@ -0,0 +1,23 @@
+import { afterEach, describe, expect, it } from "vitest";
+import { mergeMissing } from "./legacy.shared.js";
+
+describe("mergeMissing prototype pollution guard", () => {
+  afterEach(() => {
+    delete (Object.prototype as Record<string, unknown>).polluted;
+  });
+
+  it("ignores __proto__ keys without polluting Object.prototype", () => {
+    const target = { safe: { keep: true } } as Record<string, unknown>;
+    const source = JSON.parse('{"safe":{"next":1},"__proto__":{"polluted":true}}') as Record<
+      string,
+      unknown
+    >;
+
+    mergeMissing(target, source);
+
+    expect((target.safe as Record<string, unknown>).keep).toBe(true);
+    expect((target.safe as Record<string, unknown>).next).toBe(1);
+    expect(target.polluted).toBeUndefined();
+    expect((Object.prototype as Record<string, unknown>).polluted).toBeUndefined();
+  });
+});
diff --git a/src/config/legacy.shared.ts b/src/config/legacy.shared.ts
index 3ffe911cff7..9a7e33c8f3f 100644
--- a/src/config/legacy.shared.ts
+++ b/src/config/legacy.shared.ts
@@ -12,6 +12,7 @@ export type LegacyConfigMigration = {
 
 import { isSafeExecutableValue } from "../infra/exec-safety.js";
 import { isRecord } from "../utils.js";
+import { isBlockedObjectKey } from "./prototype-keys.js";
 export { isRecord };
 
 export const getRecord = (value: unknown): Record<string, unknown> | null =>
@@ -32,7 +33,7 @@ export const ensureRecord = (
 
 export const mergeMissing = (target: Record<string, unknown>, source: Record<string, unknown>) => {
   for (const [key, value] of Object.entries(source)) {
-    if (value === undefined) {
+    if (value === undefined || isBlockedObjectKey(key)) {
       continue;
     }
     const existing = target[key];
diff --git a/src/config/merge-patch.proto-pollution.test.ts b/src/config/merge-patch.proto-pollution.test.ts
index 65a0798225f..ebd01fb3553 100644
--- a/src/config/merge-patch.proto-pollution.test.ts
+++ b/src/config/merge-patch.proto-pollution.test.ts
@@ -9,6 +9,7 @@ describe("applyMergePatch prototype pollution guard", () => {
     expect(result.b).toBe(2);
     expect(result.a).toBe(1);
     expect(Object.prototype.hasOwnProperty.call(result, "__proto__")).toBe(false);
+    expect(result.polluted).toBeUndefined();
     expect(({} as Record<string, unknown>).polluted).toBeUndefined();
   });
 
@@ -35,6 +36,7 @@ describe("applyMergePatch prototype pollution guard", () => {
     expect(result.nested.y).toBe(2);
     expect(result.nested.x).toBe(1);
     expect(Object.prototype.hasOwnProperty.call(result.nested, "__proto__")).toBe(false);
+    expect(result.nested.polluted).toBeUndefined();
     expect(({} as Record<string, unknown>).polluted).toBeUndefined();
   });
 });
diff --git a/src/config/merge-patch.ts b/src/config/merge-patch.ts
index 3d06635ae62..e0aa8caca01 100644
--- a/src/config/merge-patch.ts
+++ b/src/config/merge-patch.ts
@@ -1,10 +1,8 @@
 import { isPlainObject } from "../utils.js";
+import { isBlockedObjectKey } from "./prototype-keys.js";
 
 type PlainObject = Record<string, unknown>;
 
-/** Keys that must never be merged to prevent prototype-pollution attacks. */
-const BLOCKED_KEYS = new Set(["__proto__", "constructor", "prototype"]);
-
 type MergePatchOptions = {
   mergeObjectArraysById?: boolean;
 };
@@ -73,7 +71,7 @@ export function applyMergePatch(
   const result: PlainObject = isPlainObject(base) ? { ...base } : {};
 
   for (const [key, value] of Object.entries(patch)) {
-    if (BLOCKED_KEYS.has(key)) {
+    if (isBlockedObjectKey(key)) {
       continue;
     }
     if (value === null) {