diff -ru dnsdist-1.9.12.orig/dnsdist-backend.cc dnsdist-1.9.12.CVE-2026-33602/dnsdist-backend.cc
--- dnsdist-1.9.12.orig/dnsdist-backend.cc	2026-03-13 16:09:16.000000000 +0100
+++ dnsdist-1.9.12.CVE-2026-33602/dnsdist-backend.cc	2026-04-03 15:35:10.833485998 +0200
@@ -557,7 +557,7 @@
 
   do {
     uint16_t selectedID = (idOffset++) % idStates.size();
-    IDState& ids = idStates[selectedID];
+    IDState& ids = idStates.at(selectedID);
     auto guard = ids.acquire();
     if (!guard) {
       continue;
@@ -600,7 +600,7 @@
     return;
   }
 
-  auto& ids = idStates[id];
+  auto& ids = idStates.at(id);
   auto guard = ids.acquire();
   if (!guard) {
     /* already used */
@@ -639,11 +639,11 @@
     return result;
   }
 
-  if (id > idStates.size()) {
+  if (id >= idStates.size()) {
     return result;
   }
 
-  auto& ids = idStates[id];
+  auto& ids = idStates.at(id);
   auto guard = ids.acquire();
   if (!guard) {
     return result;