--- tmux-1.6/tmux.c.bak	2012-01-30 12:55:27.533745642 -0500
+++ tmux-1.6/tmux.c	2012-01-30 12:57:06.285028356 -0500
@@ -237,6 +237,7 @@
 	struct passwd	*pw;
 	char		*s, *path, *label, *home, **var;
 	int	 	 opt, flags, quiet, keys;
+    u_int    gid;
 
 #if defined(DEBUG) && defined(__OpenBSD__)
 	malloc_options = (char *) "AFGJPX";
@@ -390,6 +391,12 @@
 			}
 		}
 	}
+	gid = getgid();
+	/* drop unnecessary privileges which were needed for makesocketpath() 
+	 * to create the user directory under /var/run/tmux which is only
+	 * writeable for processes that have setgid utmp. */
+	if (setresgid(gid, gid, gid) != 0)
+		return (NULL);
 	if (label != NULL)
 		xfree(label);
 	if (realpath(path, socket_path) == NULL)