# UNDF: UNDF-2026-000000032
diff --git a/Source/cmComputeLinkDepends.cxx b/Source/cmComputeLinkDepends.cxx
index d2da7ec..0d785a1 100644
--- a/Source/cmComputeLinkDepends.cxx
+++ b/Source/cmComputeLinkDepends.cxx
@@ -1075,6 +1075,8 @@ void cmComputeLinkDepends::AddLinkEntries(cm::optional<size_t> depender_index,
       assert(group);
       dependee_index = group->first;
       if (group->second) {
+        this->GroupItemSets.emplace(group->first,
+          std::unordered_set<size_t>(groupItems.begin(), groupItems.end()));
         this->GroupItems.emplace(group->first, std::move(groupItems));
       }
       group = cm::nullopt;
@@ -1164,8 +1166,7 @@ void cmComputeLinkDepends::AddLinkEntries(cm::optional<size_t> depender_index,
           if (groupFeature == currentFeature) {
             continue;
           }
-          if (std::find(g.second.cbegin(), g.second.cend(), dependee_index) !=
-              g.second.cend()) {
+          if (this->GroupItemSets.at(g.first).count(dependee_index)) {
             this->CMakeInstance->IssueMessage(
               MessageType::FATAL_ERROR,
               cmStrCat("Impossible to link target '", this->Target->GetName(),
@@ -1360,9 +1361,8 @@ void cmComputeLinkDepends::UpdateGroupDependencies()
       }
       // search the item in the defined groups
       for (auto const& groupItems : this->GroupItems) {
-        auto pos = std::find(groupItems.second.cbegin(),
-                             groupItems.second.cend(), index);
-        if (pos != groupItems.second.cend()) {
+        // CWE-407 fix: O(1) set lookup replaces O(n) std::find scan
+        if (this->GroupItemSets.at(groupItems.first).count(index)) {
           // replace lib dependency by the group it belongs to
           edge = cmGraphEdge{ groupItems.first, false, false,
                               cmListFileBacktrace() };
diff --git a/Source/cmComputeLinkDepends.h b/Source/cmComputeLinkDepends.h
index f2162cf..b31e3b4 100644
--- a/Source/cmComputeLinkDepends.h
+++ b/Source/cmComputeLinkDepends.h
@@ -10,6 +10,8 @@
 #include <queue>
 #include <set>
 #include <string>
+#include <unordered_map>
+#include <unordered_set>
 #include <utility>
 #include <vector>
 
@@ -123,6 +125,8 @@ private:
 
   // map storing, for each group, the list of items
   std::map<size_t, std::vector<size_t>> GroupItems;
+  // CWE-407 fix: O(1) set for GroupItems membership checks (std::find was O(n))
+  std::unordered_map<size_t, std::unordered_set<size_t>> GroupItemSets;
 
   // BFS of initial dependencies.
   struct BFSEntry