# UNDF: UNDF-2026-000000340
--- a/src/plugins/irc/irc-channel.h
+++ b/src/plugins/irc/irc-channel.h
@@ -85,6 +85,7 @@ struct t_irc_channel
     struct t_irc_nick *nicks;           /* nicks on channel                */
     int nicks_count;                    /* number of nicks on channel       */
+    struct t_hashtable *nicks_hashtable;/* nick_name(lower) → t_irc_nick*  */
     struct t_irc_nick *last_nick;       /* last nick on channel             */

--- a/src/plugins/irc/irc-nick.c
+++ b/src/plugins/irc/irc-nick.c
@@ -533,6 +533,14 @@ irc_nick_new_in_channel (struct t_irc_server *server,
                          struct t_irc_channel *channel, ...)
 {
+    /* maintain hashtable for O(1) lookups */
+    if (!channel->nicks_hashtable)
+        channel->nicks_hashtable = weechat_hashtable_new (
+            64,
+            WEECHAT_HASHTABLE_STRING, WEECHAT_HASHTABLE_POINTER,
+            NULL, NULL);
+
     /* ... existing insertion code ... */
+    if (channel->nicks_hashtable)
+    {
+        char lower[512];
+        irc_server_casemap_lower (server, new_nick->name, lower, sizeof (lower));
+        weechat_hashtable_set (channel->nicks_hashtable, lower, new_nick);
+    }
 }

@@ -808,6 +808,11 @@ irc_nick_free (struct t_irc_server *server, struct t_irc_channel *channel,
                struct t_irc_nick *nick)
 {
+    /* remove from hashtable */
+    if (channel->nicks_hashtable)
+    {
+        char lower[512];
+        irc_server_casemap_lower (server, nick->name, lower, sizeof (lower));
+        weechat_hashtable_remove (channel->nicks_hashtable, lower);
+    }
     /* ... existing removal code ... */
 }

@@ -830,12 +830,16 @@ irc_nick_search (struct t_irc_server *server, struct t_irc_channel *channel,
                  const char *nickname)
 {
-    struct t_irc_nick *ptr_nick;
-
     if (!channel || !nickname)
         return NULL;

-    for (ptr_nick = channel->nicks; ptr_nick;
-         ptr_nick = ptr_nick->next_nick)
-    {
-        if (irc_server_strcasecmp (server, ptr_nick->name, nickname) == 0)
-            return ptr_nick;
-    }
-    return NULL;
+    /* CWE-407 fix: O(1) hash lookup instead of O(n) linked-list scan */
+    if (channel->nicks_hashtable)
+    {
+        char lower[512];
+        irc_server_casemap_lower (server, nickname, lower, sizeof (lower));
+        return (struct t_irc_nick *)weechat_hashtable_get (
+            channel->nicks_hashtable, lower);
+    }
+
+    /* fallback: hashtable not yet built (channel being initialised) */
+    struct t_irc_nick *ptr_nick;
+    for (ptr_nick = channel->nicks; ptr_nick; ptr_nick = ptr_nick->next_nick)
+        if (irc_server_strcasecmp (server, ptr_nick->name, nickname) == 0)
+            return ptr_nick;
+    return NULL;
 }