1 files changed, 9 insertions, 1 deletions
diff --git a/src/validation.cpp b/src/validation.cpp
index d19521bd3..78eb6d730 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -3079,13 +3079,15 @@ static bool AcceptBlockHeader(const CBlockHeader& block, CValidationState& state
 }
 
 // Exposed wrapper for AcceptBlockHeader
-bool ProcessNewBlockHeaders(const std::vector<CBlockHeader>& headers, CValidationState& state, const CChainParams& chainparams, const CBlockIndex** ppindex)
+bool ProcessNewBlockHeaders(const std::vector<CBlockHeader>& headers, CValidationState& state, const CChainParams& chainparams, const CBlockIndex** ppindex, CBlockHeader *first_invalid)
 {
+    if (first_invalid != nullptr) first_invalid->SetNull();
     {
         LOCK(cs_main);
         for (const CBlockHeader& header : headers) {
             CBlockIndex *pindex = nullptr; // Use a temp pindex instead of ppindex to avoid a const_cast
             if (!AcceptBlockHeader(header, state, chainparams, &pindex)) {
+                if (first_invalid) *first_invalid = header;
                 return false;
             }
             if (ppindex) {
@@ -3135,6 +3137,12 @@ static bool AcceptBlock(const std::shared_ptr<const CBlock>& pblock, CValidation
         if (pindex->nTx != 0) return true;  // This is a previously-processed block that was pruned
         if (!fHasMoreWork) return true;     // Don't process less-work chains
         if (fTooFarAhead) return true;      // Block height is too high
+
+        // Protect against DoS attacks from low-work chains.
+        // If our tip is behind, a peer could try to send us
+        // low-work blocks on a fake chain that we would never
+        // request; don't process these.
+        if (pindex->nChainWork < nMinimumChainWork) return true;
     }
     if (fNewBlock) *fNewBlock = true;