diff --git a/packages/eth-json-rpc-middleware/CHANGELOG.md b/packages/eth-json-rpc-middleware/CHANGELOG.md
index 86c71ec6dce..62d436f4187 100644
--- a/packages/eth-json-rpc-middleware/CHANGELOG.md
+++ b/packages/eth-json-rpc-middleware/CHANGELOG.md
@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Changed
+
+- Add more strict validation for signTypedData V4 requests ([#8526](https://github.com/MetaMask/core/pull/8526))
+
 ## [23.1.1]
 
 ### Changed
diff --git a/packages/eth-json-rpc-middleware/src/utils/validation.test.ts b/packages/eth-json-rpc-middleware/src/utils/validation.test.ts
index 8191436037b..0b572b9a31d 100644
--- a/packages/eth-json-rpc-middleware/src/utils/validation.test.ts
+++ b/packages/eth-json-rpc-middleware/src/utils/validation.test.ts
@@ -8,6 +8,7 @@ import {
   resemblesAddress,
   validateAndNormalizeKeyholder,
   validateParams,
+  validateTypedMessageKeys,
 } from './validation';
 
 jest.mock('@metamask/superstruct', () => ({
@@ -125,4 +126,39 @@ describe('Validation Utils', () => {
       `);
     });
   });
+
+  describe('validateTypedMessageKeys', () => {
+    it('does not throw for data with only schema-defined keys', () => {
+      const data = JSON.stringify({
+        types: {
+          EIP712Domain: [{ name: 'name', type: 'string' }],
+        },
+      });
+
+      expect(() => validateTypedMessageKeys(data)).not.toThrow();
+    });
+
+    it('throws for data with extraneous keys', () => {
+      const data = JSON.stringify({
+        types: {
+          EIP712Domain: [{ name: 'name', type: 'string' }],
+        },
+        primaryType: 'EIP712Domain',
+        domain: {},
+        message: {},
+        extraKey: 'unexpected',
+      });
+
+      expect(() => validateTypedMessageKeys(data)).toThrow('Invalid input.');
+    });
+
+    it('throws when data contains only extraneous keys', () => {
+      const data = JSON.stringify({
+        foo: 'bar',
+        baz: 123,
+      });
+
+      expect(() => validateTypedMessageKeys(data)).toThrow('Invalid input.');
+    });
+  });
 });
diff --git a/packages/eth-json-rpc-middleware/src/utils/validation.ts b/packages/eth-json-rpc-middleware/src/utils/validation.ts
index 7d291aec56c..f65a6bc41ba 100644
--- a/packages/eth-json-rpc-middleware/src/utils/validation.ts
+++ b/packages/eth-json-rpc-middleware/src/utils/validation.ts
@@ -1,3 +1,4 @@
+import { TYPED_MESSAGE_SCHEMA } from '@metamask/eth-sig-util';
 import { providerErrors, rpcErrors } from '@metamask/rpc-errors';
 import type { Struct, StructError } from '@metamask/superstruct';
 import { validate } from '@metamask/superstruct';
@@ -187,3 +188,23 @@ export function validateTypedDataForPrototypePollution(data: string): void {
     checkObjectForPrototypePollution(message);
   }
 }
+
+/**
+ * Validates that EIP-712 typed message data contains only keys defined in
+ * the TYPED_MESSAGE_SCHEMA from `@metamask/eth-sig-util`. Rejects messages
+ * with extraneous top-level keys.
+ *
+ * @param data - The stringified typed data to validate.
+ * @throws rpcErrors.invalidInput() if extraneous keys are detected.
+ */
+export function validateTypedMessageKeys(data: string): void {
+  const parsedData = parseTypedMessage(data);
+  const allowedKeys = new Set(Object.keys(TYPED_MESSAGE_SCHEMA.properties));
+  const hasExtraneousKey = Object.keys(parsedData).some(
+    (key) => !allowedKeys.has(key),
+  );
+
+  if (hasExtraneousKey) {
+    throw rpcErrors.invalidInput();
+  }
+}
diff --git a/packages/eth-json-rpc-middleware/src/wallet.test.ts b/packages/eth-json-rpc-middleware/src/wallet.test.ts
index 3c8d69fd36e..a9964c0d3a1 100644
--- a/packages/eth-json-rpc-middleware/src/wallet.test.ts
+++ b/packages/eth-json-rpc-middleware/src/wallet.test.ts
@@ -757,6 +757,29 @@ describe('wallet', () => {
         engine.handle(...createHandleParams(payload)),
       ).rejects.toThrow('Invalid input.');
     });
+
+    it('should throw if message data contains extraneous keys', async () => {
+      const getAccounts = async (): Promise<string[]> => testAddresses.slice();
+      const processTypedMessageV4 = async (): Promise<string> => testMsgSig;
+      const engine = JsonRpcEngineV2.create({
+        middleware: [
+          createWalletMiddleware({ getAccounts, processTypedMessageV4 }),
+        ],
+      });
+
+      const messageParams = getMsgParams();
+      const payload = {
+        method: 'eth_signTypedData_v4',
+        params: [
+          testAddresses[0],
+          JSON.stringify({ ...messageParams, extraKey: 'unexpected' }),
+        ],
+      };
+
+      await expect(
+        engine.handle(...createHandleParams(payload)),
+      ).rejects.toThrow('Invalid input.');
+    });
   });
 
   describe('sign', () => {
diff --git a/packages/eth-json-rpc-middleware/src/wallet.ts b/packages/eth-json-rpc-middleware/src/wallet.ts
index 24394190640..b220be16e09 100644
--- a/packages/eth-json-rpc-middleware/src/wallet.ts
+++ b/packages/eth-json-rpc-middleware/src/wallet.ts
@@ -25,6 +25,7 @@ import {
   validateAndNormalizeKeyholder as validateKeyholder,
   validateTypedDataForPrototypePollution,
   validateTypedDataV1ForPrototypePollution,
+  validateTypedMessageKeys,
 } from './utils/validation';
 
 export type TransactionParams = {
@@ -408,6 +409,7 @@ export function createWalletMiddleware({
 
     const address = await validateAndNormalizeKeyholder(params[0], context);
     const message = normalizeTypedMessage(params[1]);
+    validateTypedMessageKeys(message);
     validatePrimaryType(message);
     validateVerifyingContract(message);
     validateTypedDataForPrototypePollution(message);