Made sure major_version of Cryptonote header is correct.

src/validation.cpp

@@ -3038,6 +3038,10 @@ static bool FindUndoPos(CValidationState &state, int nFile, CDiskBlockPos &pos,
 
 static bool CheckBlockHeader(const CBlockHeader& block, CValidationState& state, const Consensus::Params& consensusParams, bool fCheckPOW = true)
 {
+    if (block.cnHeader.major_version != consensusParams.GetCryptonoteMajorVersion()) {
+        return state.Invalid(false, 0, "incorrect-major-version", "Cryptonote major version incorrect");
+    }
+
     // Check proof of work matches claimed amount
     if (fCheckPOW && !CheckProofOfWork(block.GetPoWHash(), block.nBits, consensusParams))
         return state.DoS(50, false, REJECT_INVALID, "high-hash", false, "proof of work failed");