diff --git a/src/processing/plugins/dummy_processor.cc b/src/processing/plugins/dummy_processor.cc
index fbbf523141c5..0e060f05b7d5 100644
--- a/src/processing/plugins/dummy_processor.cc
+++ b/src/processing/plugins/dummy_processor.cc
@@ -8,7 +8,11 @@ using std::cout;
 using std::endl;
 
 const char kSignature[] = "NVDADAM1";  // DAM (Direct Accessible Marshalling) V1
-const int kPrefixLen = 24;
+const int64_t kPrefixLen = 24;
+
+bool ValidDam(std::int8_t *buffer) {
+    return memcmp(buffer, kSignature, strlen(kSignature)) == 0;
+}
 
 xgboost::common::Span<int8_t> DummyProcessor::ProcessGHPairs(vector<double> &pairs) {
     cout << "ProcessGHPairs called with pairs size: " << pairs.size() << endl;
@@ -31,13 +35,18 @@ xgboost::common::Span<int8_t> DummyProcessor::ProcessGHPairs(vector<double> &pai
     }
 
     // Save pairs for future operations
-    this->gh_pairs_ = &pairs;
+    this->gh_pairs_ = new vector<double>(pairs);
 
     return xgboost::common::Span<int8_t>(reinterpret_cast<int8_t *>(buf), buf_size);
 }
 
 xgboost::common::Span<int8_t> DummyProcessor::HandleGHPairs(xgboost::common::Span<int8_t> buffer) {
-    cout << "HandleGHPairs called with buffer size: " << buffer.size() << endl;
+    cout << "HandleGHPairs called with buffer size: " << buffer.size() << " Active: " << active_ << endl;
+
+    if (!ValidDam(buffer.data())) {
+        cout << "Invalid buffer received" << endl;
+        return buffer;
+    }
 
     // For dummy, this call is used to set gh_pairs for passive sites
     if (!active_) {
@@ -48,6 +57,7 @@ xgboost::common::Span<int8_t> DummyProcessor::HandleGHPairs(xgboost::common::Spa
         for (int i = 0; i < num; i += 10) {
             gh_pairs_->push_back(pairs[i]);
         }
+        cout << "GH Pairs saved. Size: " << gh_pairs_->size() << endl;
     }
 
     return buffer;
@@ -58,6 +68,7 @@ xgboost::common::Span<std::int8_t> DummyProcessor::ProcessAggregation(
     auto total_bin_size = gidx_->Cuts().Values().size();
     auto histo_size = total_bin_size*2;
     auto buf_size = kPrefixLen + 8*histo_size*nodes_to_build.size();
+    cout << "ProcessAggregation called with bin size: " << total_bin_size << " Buffer Size: " << buf_size << endl;
     std::int8_t *buf = static_cast<std::int8_t *>(calloc(buf_size, 1));
     memcpy(buf, kSignature, strlen(kSignature));
     memcpy(buf + 8, &buf_size, 8);
@@ -74,6 +85,15 @@ xgboost::common::Span<std::int8_t> DummyProcessor::ProcessAggregation(
                     continue;
                 }
 
+                if (slot >= total_bin_size) {
+                    cout << "Slot too big, ignored: " << slot << endl;
+                    continue;
+                }
+
+                if (row_id >= gh_pairs_->size()/2) {
+                    cout << "Row ID too big: " << row_id << endl;
+                }
+
                 auto g = (*gh_pairs_)[row_id*2];
                 auto h = (*gh_pairs_)[row_id*2+1];
                 histo[slot*2] += g;
@@ -86,17 +106,29 @@ xgboost::common::Span<std::int8_t> DummyProcessor::ProcessAggregation(
     return xgboost::common::Span<int8_t>(reinterpret_cast<int8_t *>(buf), buf_size);
 }
 
-std::vector<double> DummyProcessor::HandleAggregation(std::vector<xgboost::common::Span<std::int8_t>> buffers) {
+std::vector<double> DummyProcessor::HandleAggregation(xgboost::common::Span<std::int8_t> buffer) {
+    cout << "HandleAggregation called with buffer size: " << buffer.size() << endl;
     std::vector<double> result = std::vector<double>();
 
-    for (auto buf : buffers) {
-        int8_t *ptr = buf.data();
+    int8_t* ptr = buffer.data();
+    auto rest_size = buffer.size();
+
+    while (rest_size > kPrefixLen) {
+        if (!ValidDam(ptr)) {
+            cout << "Invalid buffer at offset " << buffer.size() - rest_size << endl;
+            continue;
+        }
         std::int64_t *size_ptr = reinterpret_cast<std::int64_t *>(ptr + 8);
         double *array_start = reinterpret_cast<double *>(ptr + kPrefixLen);
-        auto array_size = (*size_ptr - kPrefixLen) / 8;
+        auto array_size = (*size_ptr - kPrefixLen)/8;
+        cout << "Histo size for buffer: " << array_size << endl;
         result.insert(result.end(), array_start, array_start + array_size);
+        cout << "Result size: " << result.size() << endl;
+        rest_size -= *size_ptr;
+        ptr = ptr + *size_ptr;
     }
+
+    cout << "Total histo size: " << result.size() << endl;
     
     return result;
 }
-
diff --git a/src/processing/plugins/dummy_processor.h b/src/processing/plugins/dummy_processor.h
index dc1d937ba4d0..9511cf7f56f6 100644
--- a/src/processing/plugins/dummy_processor.h
+++ b/src/processing/plugins/dummy_processor.h
@@ -40,5 +40,5 @@ class DummyProcessor: public xgboost::processing::Processor {
     xgboost::common::Span<std::int8_t> ProcessAggregation(std::vector<xgboost::bst_node_t> const &nodes_to_build,
                                                           xgboost::common::RowSetCollection const &row_set) override;
 
-    std::vector<double> HandleAggregation(std::vector<xgboost::common::Span<std::int8_t>> buffers) override;
+    std::vector<double> HandleAggregation(xgboost::common::Span<std::int8_t> buffer) override;
 };
diff --git a/src/processing/processor.h b/src/processing/processor.h
index effc52c6ff7d..beaabb89c5bd 100644
--- a/src/processing/processor.h
+++ b/src/processing/processor.h
@@ -17,8 +17,8 @@ const char kDummyProcessor[] = "dummy";
 const char kLoadFunc[] = "LoadProcessor";
 
 //  Data type definition
-const int kDataTypeGHPairs = 1;
-const int kDataTypeHisto = 2;
+const int64_t kDataTypeGHPairs = 1;
+const int64_t kDataTypeHisto = 2;
 
 /*! \brief An processor interface to handle tasks that require external library through plugins */
 class Processor {
@@ -82,12 +82,12 @@ class Processor {
     /*!
      * \brief Handle all gather result
      *
-     * \param buffers Buffer from all gather, only buffer from active site is needed
+     * \param buffer Buffer from all gather, only buffer from active site is needed
      *
      * \return A flattened vector of histograms for each site, each node in the form of
      *     site1_node1, site1_node2 site1_node3, site2_node1, site2_node2, site2_node3
      */
-    virtual std::vector<double> HandleAggregation(std::vector<common::Span<std::int8_t>> buffers) = 0;
+    virtual std::vector<double> HandleAggregation(xgboost::common::Span<std::int8_t> buffer) = 0;
 };
 
 class ProcessorLoader {