--- tk8.4.17/generic/tkImgGIF.c.orig	2008-02-14 23:20:53.683962654 +0000
+++ tk8.4.17/generic/tkImgGIF.c	2008-02-14 23:21:42.762759495 +0000
@@ -826,6 +826,12 @@
 		Tcl_PosixError(interp), (char *) NULL);
 	return TCL_ERROR;
     }
+
+    if (initialCodeSize > MAX_LWZ_BITS) {
+	Tcl_SetResult(interp, "malformed image", TCL_STATIC);
+	return TCL_ERROR;
+    }
+
     if (transparent != -1) {
 	cmap[transparent][CM_RED] = 0;
 	cmap[transparent][CM_GREEN] = 0;