commit 312f0f9c12f26fbe015cd0e6cefa40e4b99017d9
Author: Michael R Sweet <michael.r.sweet@gmail.com>
Date:   Fri Jan 7 18:21:53 2022 -0500

    Block GIF images with a code size > 12 (Issue #463)

Index: htmldoc-1.9.11/htmldoc/image.cxx
===================================================================
--- htmldoc-1.9.11.orig/htmldoc/image.cxx	2022-02-26 01:11:13.177259451 +0100
+++ htmldoc-1.9.11/htmldoc/image.cxx	2022-02-26 01:11:13.173259454 +0100
@@ -293,6 +293,12 @@
   pass      = 0;
   code_size = (uchar)getc(fp);
 
+  if (code_size > 12)
+  {
+    progress_error(HD_ERROR_READ_ERROR, "Bad GIF file \"%s\" - invalid code size %d.", img->filename, code_size);
+    return (-1);
+  }
+
   if (gif_read_lzw(fp, 1, code_size) < 0)
     return (-1);
 
@@ -420,7 +426,7 @@
   if (sp > stack)
     return (*--sp);
 
-  while ((code = gif_get_code (fp, code_size, 0)) >= 0)
+  while ((code = gif_get_code(fp, code_size, 0)) >= 0)
   {
     if (code == clear_code)
     {