Patch from Gentoo:
http://sources.gentoo.org/cgi-bin/viewvc.cgi/gentoo-x86/media-libs/gd/files/gd-2.0.35-maxcolors.patch?view=log

http://bugs.gentoo.org/292130

fix in usptream repo already

--- gd-2.0.35/gd_gd.c
+++ gd-2.0.35/gd_gd.c
@@ -44,6 +44,10 @@
 	    {
 	      goto fail1;
 	    }
+	  if (im->colorsTotal > gdMaxColors)
+	    {
+		   goto fail1;
+		 }
 	}
       /* Int to accommodate truecolor single-color transparency */
       if (!gdGetInt (&im->transparent, in))
