Harden attestation payload parsing (#34)

Co-authored-by: OpenCode <opencode-noreply@coinbase.com>

Author: leopoldjoy

src/NitroValidator.sol

@@ -212,11 +212,17 @@ contract NitroValidator {
                 // be present (do not silently stop at the payload end on a missing break), and stop
                 // exclusively on it.
                 require(current.end() < end, "missing break marker");
-                if (uint8(attestationTbs[current.end()]) == 0xff) break;
+                if (uint8(attestationTbs[current.end()]) == 0xff) {
+                    require(current.end() + 1 == end, "trailing payload bytes");
+                    break;
+                }
             } else {
                 // A definite-length map ends after exactly `entryCount` entries; a stray 0xFF must
                 // not terminate it early (it would be parsed as a key and rejected as a non-string).
-                if (entry == entryCount) break;
+                if (entry == entryCount) {
+                    require(current.end() == end, "trailing payload bytes");
+                    break;
+                }
             }
             current = attestationTbs.nextTextString(current);
             bytes32 keyHash = attestationTbs.keccak(current);

test/IndefiniteLengthCbor.t.sol

@@ -835,6 +835,22 @@ contract NitroValidatorIndefiniteLengthTest is Test {
         validator.parseAttestation(tbs);
     }
 
+    /// @dev Definite-length outer maps must consume the whole payload byte string; trailing bytes
+    ///      after the declared entries are malformed, even if the declared prefix parses cleanly.
+    function test_neg_definiteOuterMapTrailingBytes_reverts() public {
+        bytes memory tbs = _buildTbs(abi.encodePacked(hex"a2", _partialEntries(), hex"00"));
+        vm.expectRevert("trailing payload bytes");
+        validator.parseAttestation(tbs);
+    }
+
+    /// @dev Indefinite-length outer maps must end immediately after their 0xFF break marker; bytes
+    ///      after the break are not silently ignored.
+    function test_neg_indefiniteOuterMapTrailingBytesAfterBreak_reverts() public {
+        bytes memory tbs = _buildTbs(abi.encodePacked(CBOR_MAP_INDEFINITE, _partialEntries(), CBOR_BREAK, hex"00"));
+        vm.expectRevert("trailing payload bytes");
+        validator.parseAttestation(tbs);
+    }
+
     /// @dev Empty indefinite-length inner cabundle array ([0x9F, 0xFF]) parses as an
     ///      empty cabundle and the outer loop continues.
     function test_nestedIndefiniteEmptyArray_parses() public view {