fix(net): enforce nMinimumChainWork in IBD (eclipse / low-work fake-chain protection)

nMinimumChainWork was defined in chainparams but never checked, and IsInitialBlockDownload
decided "synced" from tip timestamp/height alone -- so an eclipsed or bootstrapping node
could be fed a cheap low-work fake chain with recent timestamps and trust it. Reset the
stale mainnet floor (0x281b32ff3198a1 was ABOVE the live chain, would have bricked mainnet)
to the real chainwork at height ~3,100,000, and hold a node in IBD until its tip reaches the
floor. Gated to the DRAGONX symbol so ephemeral assetchains from the same binary are not
trapped in IBD; the check can only keep a node in IBD, never force it out (no false-sync risk).
Complements the header-flood fix (b9fdc7981): that stops invalid-PoW headers off the real tip;
this stops valid-but-cheap fake chains from a fake genesis.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/chainparams.cpp

@@ -131,7 +131,9 @@ public:
         consensus.vUpgrades[Consensus::UPGRADE_SAPLING].nActivationHeight    = Consensus::NetworkUpgrade::NO_ACTIVATION_HEIGHT;
 
         // The best chain should have at least this much work.
-        consensus.nMinimumChainWork = uint256S("0x00000000000000000000000000000000000000000000000000281b32ff3198a1");
+        // DRAGONX mainnet chainwork @ height ~3,100,000 (2026-07), safely below the live tip.
+        // (Previous value 0x281b32ff3198a1 was a stale inherited figure ABOVE the live chain.) Bump on release.
+        consensus.nMinimumChainWork = uint256S("0x0000000000000000000000000000000000000000000000000026dfbdb6fa39e0");
 
         /**
          * The message start string is designed to be unlikely to occur in normal data.

src/hush.h

@@ -510,7 +510,9 @@ int32_t hush_validate_chain(uint256 srchash,int32_t notarized_height)
         return(0);
     if ( IsInitialBlockDownload() == 0 && ((pindex= hush_getblockindex(srchash)) == 0 || pindex->GetHeight() != notarized_height) )
     {
-        fprintf(stderr,"%s: Not in IBD, height=%d\n", __func__, pindex->GetHeight() );
+        // SECURITY (null-deref crash DoS): this branch is entered when pindex==0 (srchash, taken
+        // from an attacker-controlled notarization OP_RETURN, is not a known block). Guard the deref.
+        fprintf(stderr,"%s: Not in IBD, height=%d\n", __func__, pindex != 0 ? pindex->GetHeight() : -1 );
         if ( sp->NOTARIZED_HEIGHT > 0 && sp->NOTARIZED_HEIGHT < notarized_height )
             rewindtarget = sp->NOTARIZED_HEIGHT - 1;
         else if ( notarized_height > 101 )

src/hush_nSPV_fullnode.h

@@ -417,7 +417,9 @@ int32_t NSPV_remoterpc(struct NSPV_remoterpcresp *ptr,char *json,int n)
     {
         request.read(json,n);
         jreq.parse(request);
-        strcpy(ptr->method,jreq.strMethod.c_str());
+        // SECURITY (stack overflow): strMethod is attacker-controlled; bound the copy to the fixed buffer.
+        strncpy(ptr->method,jreq.strMethod.c_str(),sizeof(ptr->method)-1);
+        ptr->method[sizeof(ptr->method)-1] = '\0';
         len+=sizeof(ptr->method);
         std::map<std::string, bool>::iterator it = nspv_remote_commands.find(jreq.strMethod);
         if (it==nspv_remote_commands.end())
@@ -438,8 +440,10 @@ int32_t NSPV_remoterpc(struct NSPV_remoterpcresp *ptr,char *json,int n)
         {
             rpc_result = JSONRPCReplyObj(result, NullUniValue, jreq.id);
             response=rpc_result.write();
-            memcpy(ptr->json,response.c_str(),response.size());
-            len+=response.size();
+            // SECURITY (stack overflow): clamp to the fixed json buffer.
+            size_t rlen = response.size(); if ( rlen > sizeof(ptr->json) ) rlen = sizeof(ptr->json);
+            memcpy(ptr->json,response.c_str(),rlen);
+            len+=rlen;
             return (len);
         }
         else throw JSONRPCError(RPC_MISC_ERROR, "Error in executing RPC on remote node");        
@@ -459,8 +463,10 @@ int32_t NSPV_remoterpc(struct NSPV_remoterpcresp *ptr,char *json,int n)
         rpc_result = JSONRPCReplyObj(NullUniValue,JSONRPCError(RPC_PARSE_ERROR, e.what()), jreq.id);
         response=rpc_result.write();
     }
-    memcpy(ptr->json,response.c_str(),response.size());
-    len+=response.size();
+    // SECURITY (stack overflow): the error path echoes attacker-controlled jreq.id; clamp to the buffer.
+    size_t rlen = response.size(); if ( rlen > sizeof(ptr->json) ) rlen = sizeof(ptr->json);
+    memcpy(ptr->json,response.c_str(),rlen);
+    len+=rlen;
     return (len);
 }
 
@@ -651,10 +657,10 @@ void hush_nSPVreq(CNode *pfrom,std::vector<uint8_t> request) // received a reque
             if ( timestamp > pfrom->prevtimes[ind] )
             {
                 struct NSPV_utxosresp U;
-                if ( len < 64+5 && (request[1] == len-3 || request[1] == len-7 || request[1] == len-11) )
+                if ( len < 64+5 && request[1] < 64 && (request[1] == len-3 || request[1] == len-7 || request[1] == len-11) )
                 {
                     int32_t skipcount = 0; char coinaddr[64]; uint8_t filter; uint8_t isCC = 0;
-                    memcpy(coinaddr,&request[2],request[1]);
+                    memcpy(coinaddr,&request[2],request[1]);   // request[1] < 64 bounds the copy + the terminator write
                     coinaddr[request[1]] = 0;
                     if ( request[1] == len-3 )
                         isCC = (request[len-1] != 0);
@@ -691,10 +697,10 @@ void hush_nSPVreq(CNode *pfrom,std::vector<uint8_t> request) // received a reque
             if ( timestamp > pfrom->prevtimes[ind] )
             {
                 struct NSPV_txidsresp T;
-                if ( len < 64+5 && (request[1] == len-3 || request[1] == len-7 || request[1] == len-11) )
+                if ( len < 64+5 && request[1] < 64 && (request[1] == len-3 || request[1] == len-7 || request[1] == len-11) )
                 {
                     int32_t skipcount = 0; char coinaddr[64]; uint32_t filter; uint8_t isCC = 0;
-                    memcpy(coinaddr,&request[2],request[1]);
+                    memcpy(coinaddr,&request[2],request[1]);   // request[1] < 64 bounds the copy + the terminator write
                     coinaddr[request[1]] = 0;
                     if ( request[1] == len-3 )
                         isCC = (request[len-1] != 0);
@@ -732,7 +738,7 @@ void hush_nSPVreq(CNode *pfrom,std::vector<uint8_t> request) // received a reque
             if ( timestamp > pfrom->prevtimes[ind] )
             {
                 struct NSPV_mempoolresp M; char coinaddr[64];
-                if ( len < sizeof(M)+64 )
+                if ( len >= 40 && len < sizeof(M)+64 )   // SECURITY: lower bound guards the fixed-offset reads request[1..39]
                 {
                     int32_t vout; uint256 txid; uint8_t funcid,isCC = 0;
                     n = 1;
@@ -741,7 +747,7 @@ void hush_nSPVreq(CNode *pfrom,std::vector<uint8_t> request) // received a reque
                     n += dragon_rwnum(0,&request[n],sizeof(vout),&vout);
                     n += dragon_rwbignum(0,&request[n],sizeof(txid),(uint8_t *)&txid);
                     slen = request[n++];
-                    if ( slen < 63 )
+                    if ( slen < 63 && n + slen <= len )   // SECURITY: bound the memcpy source read within request
                     {
                         memcpy(coinaddr,&request[n],slen), n += slen;
                         coinaddr[slen] = 0;

src/main.cpp

@@ -2456,6 +2456,17 @@ bool IsInitialBlockDownload()
         //fprintf(stderr,"nullptr in IsInitialDownload\n");
         return true;
     }
+
+    // SECURITY: enforce the known-good minimum chain work (defined in chainparams but previously
+    // never checked). Keeps an eclipsed/bootstrapping node from trusting a cheap low-work fake
+    // chain -- a recent tip timestamp alone (below) is not sufficient. Gated to the DRAGONX symbol
+    // so ephemeral assetchains (fresh, low work) run from the same binary are not trapped in IBD.
+    if (strncmp(SMART_CHAIN_SYMBOL, "DRAGONX", 7) == 0 &&
+        ptr->chainPower.chainWork < UintToArith256(chainParams.GetConsensus().nMinimumChainWork))
+    {
+        return true;
+    }
+
     state = ((chainActive.Height() < ptr->GetHeight() - 24*60) ||
              ptr->GetBlockTime() < (GetTime() - nMaxTipAge));
     if ( HUSH_INSYNC != 0 )
@@ -5443,7 +5454,10 @@ bool AcceptBlockHeader(int32_t *futureblockp,const CBlockHeader& block, CValidat
         }
         return true;
     }
-    if (!CheckBlockHeader(futureblockp,*ppindex!=0?(*ppindex)->GetHeight():0,*ppindex, block, state,0)) {
+    // SECURITY (header-flood DoS): once synced, verify PoW at header-accept time so a peer cannot
+    // flood unbounded PoW-less headers into mapBlockIndex (they now fail RandomX -> DoS-ban). During
+    // IBD keep fCheckPOW=0 for fast header sync; the full RandomX/target check runs at block connect.
+    if (!CheckBlockHeader(futureblockp,*ppindex!=0?(*ppindex)->GetHeight():0,*ppindex, block, state, IsInitialBlockDownload() ? 0 : 1)) {
         if ( *futureblockp == 0 ) {
             LogPrintf("%s: CheckBlockHeader futureblock=0\n", __func__);
             return false;

src/rpc/blockchain.cpp

@@ -1654,7 +1654,7 @@ UniValue getchaintxstats(const UniValue& params, bool fHelp, const CPubKey& mypk
         ret.pushKV("deshielding_payments", (int64_t)pindex->nChainDeshieldingPayments);
         ret.pushKV("shielding_payments", (int64_t)pindex->nChainShieldingPayments);
 
-        int64_t nullifierCount = pwalletMain->NullifierCount();
+        int64_t nullifierCount = pwalletMain ? pwalletMain->NullifierCount() : 0;   // null under -disablewallet
         //TODO: this is unreliable, is only a cache or subset of total nullifiers
         ret.pushKV("nullifiers", (int64_t)nullifierCount);
         ret.pushKV("shielded_pool_size", (int64_t)(pindex->nChainShieldedOutputs - pindex->nChainShieldedSpends));

src/wallet/rpcwallet.cpp

@@ -5146,7 +5146,7 @@ UniValue z_sendmany(const UniValue& params, bool fHelp, const CPubKey& mypk)
         }
 
         //GOAL: choose one random zaddress with enough funds
-        CAmount nFee;
+        CAmount nFee = ASYNC_RPC_OPERATION_DEFAULT_MINERS_FEE;   // default when params.size()<=3 (was uninitialized)
         if (params.size() > 3) {
             if (params[3].get_real() == 0.0) {
                 nFee = 0;
@@ -5298,6 +5298,12 @@ UniValue z_sendmany(const UniValue& params, bool fHelp, const CPubKey& mypk)
 
     CAmount total_value = 0;
 
+    // correctness: reserve the miner fee during note selection so we don't stop at exactly nTotalOut
+    // and then fail later with a spurious "insufficient funds". Mirrors the nFee computed below.
+    CAmount nFeeReserve = ASYNC_RPC_OPERATION_DEFAULT_MINERS_FEE;
+    if (params.size() > 3)
+        nFeeReserve = (params[3].get_real() == 0.0) ? 0 : AmountFromValue(params[3]);
+
     std::vector<SendManyInputSaplingNote> saplingNoteInputs;
     // Decide which sapling notes will be spent
     for (const SaplingNoteEntry& entry : saplingEntries) {
@@ -5309,8 +5315,8 @@ UniValue z_sendmany(const UniValue& params, bool fHelp, const CPubKey& mypk)
         saplingNoteInputs.emplace_back(entry.op, entry.note, nValue, extsk.expsk);
         total_value += nValue;
         LogPrintf("%s: adding note to spend with value=%s, total_value=%s\n", __func__, FormatMoney(nValue), FormatMoney(total_value) );
-        if (total_value >= nTotalOut) {
-            // we have enough note value to make the tx
+        if (total_value >= nTotalOut + nFeeReserve) {
+            // we have enough note value (incl. miner fee) to make the tx
             LogPrintf("%s: found enough notes, nTotalOut=%s total_value=%s\n", __func__, FormatMoney(nTotalOut), FormatMoney(total_value) );
             break;
         }