# UNDF: UNDF-2026-000001162
--- a/src/HttpHeader.cc
+++ b/src/HttpHeader.cc
@@ -1859,16 +1859,24 @@ void
 HttpHeader::removeConnectionHeaderEntries()
 {
     if (has(Http::HdrType::CONNECTION)) {
-        /* anything that matches Connection list member will be deleted */
+        // Build a case-insensitive set of Connection header tokens for O(1)
+        // lookup instead of O(C) strListIsMember scan per header entry.
+        // Without this, removal is O(H * C) per response hop where H is
+        // the number of HTTP headers and C is the Connection token count.
+        // A response with 50 headers and Connection: with 10 tokens costs
+        // 500 string comparisons; with a set it costs 10 inserts + 50 probes.
         String strConnection;
-
         (void) getList(Http::HdrType::CONNECTION, &strConnection);
+
+        std::unordered_set<SBuf, SBufHashCmp> connTokens;
+        const char *item = nullptr;
+        int ilen = 0;
+        const char *pos = nullptr;
+        while (strListGetItem(&strConnection, ',', &item, &ilen, &pos))
+            connTokens.emplace(item, ilen);
+
         const HttpHeaderEntry *e;
         HttpHeaderPos pos = HttpHeaderInitPos;
-        /*
-         * think: on-average-best nesting of the two loops (hdrEntry
-         * and strListItem) @?@
-         */
-        /*
-         * maybe we should delete standard stuff ("keep-alive","close")
-         * from strConnection first?
-         */
-
         int headers_deleted = 0;
         while ((e = getEntry(&pos))) {
-            if (strListIsMember(&strConnection, e->name, ','))
+            if (connTokens.count(e->name))
                 delAt(pos, headers_deleted);
         }
         if (headers_deleted)