L-03 Missing recipient Address Validation in allocateAndRegister

src/allocators/HybridAllocator.sol

@@ -159,6 +159,7 @@ contract HybridAllocator is IHybridAllocator {
         bytes32 typehash,
         bytes32 witness
     ) public payable returns (bytes32, uint256[] memory, uint256) {
+        recipient = AL.getRecipient(recipient);
         idsAndAmounts = _actualIdsAndAmounts(idsAndAmounts);
 
         (bytes32 claimHash, uint256[] memory registeredAmounts) = _COMPACT.batchDepositAndRegisterFor{value: msg.value}(

src/allocators/OnChainAllocator.sol

@@ -133,6 +133,7 @@ contract OnChainAllocator is IOnChainAllocator {
             revert InvalidExpiration(expires, block.timestamp);
         }
 
+        recipient = AL.getRecipient(recipient);
         nonce = _getAndUpdateNonce(msg.sender, recipient);
 
         uint256[2][] memory idsAndAmounts = new uint256[2][](commitments.length);

src/allocators/lib/AllocatorLib.sol

@@ -261,6 +261,13 @@ library AllocatorLib {
         return ecrecover(digest, v, r, s);
     }
 
+    function getRecipient(address recipient) internal view returns (address) {
+        assembly ("memory-safe") {
+            recipient := xor(recipient, mul(caller(), iszero(recipient)))
+        }
+        return recipient;
+    }
+
     function splitId(uint256 id) internal pure returns (uint96 allocatorId_, address token_) {
         return (splitAllocatorId(id), splitToken(id));
     }

test/HybridAllocator.t.sol

@@ -526,6 +526,35 @@ contract HybridAllocatorTest is Test, TestHelper {
         assertTrue(allocator.isClaimAuthorized(createdHash, address(0), address(0), 0, 0, new uint256[2][](0), ''));
     }
 
+    function test_allocateAndRegister_success_emptyRecipientBecomesCaller() public {
+        uint256[2][] memory idsAndAmounts = new uint256[2][](1);
+        idsAndAmounts[0][0] = _toId(Scope.Multichain, ResetPeriod.TenMinutes, address(allocator), address(usdc));
+        idsAndAmounts[0][1] = defaultAmount;
+
+        // Provide tokens
+        vm.prank(user);
+        usdc.transfer(address(allocator), defaultAmount);
+        assertEq(usdc.balanceOf(address(allocator)), defaultAmount);
+
+        vm.prank(user);
+        (bytes32 claimHash, uint256[] memory registeredAmounts, uint256 nonce) = allocator.allocateAndRegister(
+            address(0), /* allocate for an empty recipient */
+            idsAndAmounts,
+            arbiter,
+            defaultExpiration,
+            BATCH_COMPACT_TYPEHASH,
+            ''
+        );
+
+        // Ensure the allocation happened for the caller (user), not address(0)
+        assertTrue(compact.isRegistered(user, claimHash, BATCH_COMPACT_TYPEHASH));
+        assertTrue(allocator.isClaimAuthorized(claimHash, address(0), address(0), 0, 0, new uint256[2][](0), ''));
+        assertEq(registeredAmounts[0], defaultAmount);
+        assertEq(usdc.balanceOf(address(compact)), defaultAmount);
+        assertEq(compact.balanceOf(address(user), idsAndAmounts[0][0]), defaultAmount);
+        assertEq(nonce, 1);
+    }
+
     function test_allocateAndRegister_slot() public {
         uint256[2][] memory idsAndAmounts = new uint256[2][](1);
         idsAndAmounts[0][0] = _toId(Scope.Multichain, ResetPeriod.TenMinutes, address(allocator), address(0));

test/OnChainAllocator.t.sol

@@ -1505,4 +1505,36 @@ contract OnChainAllocatorTest is Test, TestHelper {
         vm.expectRevert(abi.encodeWithSelector(IOnChainAllocator.InsufficientBalance.selector, recipient, id2, 0, 1));
         allocator.attest(address(this), recipient, address(this), id2, 1);
     }
+
+    function test_allocateAndRegister_emptyRecipientBecomesCaller() public {
+        Lock[] memory commitments = new Lock[](1);
+        commitments[0] = _makeLock(address(usdc), defaultAmount);
+
+        usdc.mint(address(allocator), defaultAmount);
+
+        vm.prank(caller);
+        (bytes32 claimHash, uint256[] memory registeredAmounts, uint256 nonce) = allocator.allocateAndRegister(
+            address(0), /* allocate for an empty recipient */
+            commitments,
+            arbiter,
+            defaultExpiration,
+            BATCH_COMPACT_TYPEHASH,
+            bytes32(0)
+        );
+
+        uint256[2][] memory idsAndAmounts = new uint256[2][](1);
+        idsAndAmounts[0][0] = _toId(Scope.Multichain, ResetPeriod.TenMinutes, address(allocator), address(usdc));
+        idsAndAmounts[0][1] = defaultAmount;
+
+        assertEq(nonce, _composeNonceUint(caller, 1));
+        assertEq(registeredAmounts.length, 1);
+        assertEq(registeredAmounts[0], defaultAmount);
+        // Ensure the allocation happened for the caller, not address(0)
+        assertEq(ERC6909(address(compact)).balanceOf(caller, idsAndAmounts[0][0]), defaultAmount);
+        assertTrue(allocator.isClaimAuthorized(claimHash, arbiter, caller, nonce, defaultExpiration, idsAndAmounts, ''));
+        assertTrue(compact.isRegistered(caller, claimHash, BATCH_COMPACT_TYPEHASH));
+        bytes32 claimHashRecreated =
+            _createClaimHash(caller, arbiter, nonce, defaultExpiration, commitments, bytes32(0));
+        assertEq(claimHashRecreated, claimHash);
+    }
 }