diff -ru4N libpng-1.2.26/png.h libpng-1.2.27beta01/png.h
--- libpng-1.2.26/png.h	2008-04-02 12:27:29.867681595 -0500
+++ libpng-1.2.27beta01/png.h	2008-04-05 21:41:14.644268554 -0500
@@ -180,8 +180,11 @@
  *    1.0.31                  10    10031  10.so.0.31[.0]
  *    1.2.25                  13    10225  12.so.0.25[.0]
  *    1.2.26beta01-06         13    10226  12.so.0.26[.0]
  *    1.2.26rc01              13    10226  12.so.0.26[.0]
+ *    1.2.26                  13    10226  12.so.0.26[.0]
+ *    1.0.32                  10    10032  10.so.0.32[.0]
+ *    1.2.27beta01            13    10227  12.so.0.27[.0]
  *
  *    Henceforth the source version will match the shared-library major
  *    and minor numbers; the shared-library major version number will be
  *    used for changes in backward compatibility, as it is intended.  The
diff -ru4N libpng-1.2.26/pngpread.c libpng-1.2.27beta01/pngpread.c
--- libpng-1.2.26/pngpread.c	2008-04-05 21:37:29.944173338 -0500
+++ libpng-1.2.27beta01/pngpread.c	2008-04-05 21:41:14.898914350 -0500
@@ -1,8 +1,8 @@
 
 /* pngpread.c - read a png file in push mode
  *
- * Last changed in libpng 1.2.26 [April 2, 2008]
+ * Last changed in libpng 1.2.27 [April 6, 2008]
  * For conditions of distribution and use, see copyright notice in png.h
  * Copyright (c) 1998-2008 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
  * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
@@ -1501,11 +1501,16 @@
                  (png_charp)png_ptr->chunk_name, 
                  png_sizeof(png_ptr->unknown_chunk.name));
       png_ptr->unknown_chunk.name[png_sizeof(png_ptr->unknown_chunk.name)-1]='\0';
 
-      png_ptr->unknown_chunk.data = (png_bytep)png_malloc(png_ptr, length);
       png_ptr->unknown_chunk.size = (png_size_t)length;
-      png_crc_read(png_ptr, (png_bytep)png_ptr->unknown_chunk.data, length);
+      if (length == 0)
+         png_ptr->unknown_chunk.data = NULL;
+      else
+      {
+         png_ptr->unknown_chunk.data = (png_bytep)png_malloc(png_ptr, length);
+         png_crc_read(png_ptr, (png_bytep)png_ptr->unknown_chunk.data, length);
+      }
 #if defined(PNG_READ_USER_CHUNKS_SUPPORTED)
       if(png_ptr->read_user_chunk_fn != NULL)
       {
          /* callback to user unknown chunk handler */
@@ -1526,10 +1531,13 @@
       }
       else
 #endif
         png_set_unknown_chunks(png_ptr, info_ptr, &png_ptr->unknown_chunk, 1);
-      png_free(png_ptr, png_ptr->unknown_chunk.data);
-      png_ptr->unknown_chunk.data = NULL;
+      if (png_ptr->unknown_chunk.data)
+      {
+        png_free(png_ptr, png_ptr->unknown_chunk.data);
+        png_ptr->unknown_chunk.data = NULL;
+      }
    }
    else
 #endif
       skip=length;
diff -ru4N libpng-1.2.26/pngrutil.c libpng-1.2.27beta01/pngrutil.c
--- libpng-1.2.26/pngrutil.c	2008-04-05 21:37:32.785260077 -0500
+++ libpng-1.2.27beta01/pngrutil.c	2008-04-05 21:41:15.202296784 -0500
@@ -1,8 +1,8 @@
 
 /* pngrutil.c - utilities to read a PNG file
  *
- * Last changed in libpng 1.2.26 [April 2, 2008]
+ * Last changed in libpng 1.2.27 [April 6, 2008]
  * For conditions of distribution and use, see copyright notice in png.h
  * Copyright (c) 1998-2008 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
  * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
@@ -2226,11 +2226,16 @@
        png_memcpy((png_charp)png_ptr->unknown_chunk.name,
                   (png_charp)png_ptr->chunk_name, 
                   png_sizeof(png_ptr->unknown_chunk.name));
        png_ptr->unknown_chunk.name[png_sizeof(png_ptr->unknown_chunk.name)-1] = '\0';
-       png_ptr->unknown_chunk.data = (png_bytep)png_malloc(png_ptr, length);
        png_ptr->unknown_chunk.size = (png_size_t)length;
-       png_crc_read(png_ptr, (png_bytep)png_ptr->unknown_chunk.data, length);
+       if (length == 0)
+         png_ptr->unknown_chunk.data = NULL;
+       else
+       {
+         png_ptr->unknown_chunk.data = (png_bytep)png_malloc(png_ptr, length);
+         png_crc_read(png_ptr, (png_bytep)png_ptr->unknown_chunk.data, length);
+       }
 #if defined(PNG_READ_USER_CHUNKS_SUPPORTED)
        if(png_ptr->read_user_chunk_fn != NULL)
        {
           /* callback to user unknown chunk handler */
@@ -2251,10 +2256,13 @@
        }
        else
 #endif
          png_set_unknown_chunks(png_ptr, info_ptr, &png_ptr->unknown_chunk, 1);
-       png_free(png_ptr, png_ptr->unknown_chunk.data);
-       png_ptr->unknown_chunk.data = NULL;
+       if (png_ptr->unknown_chunk.data)
+       {
+         png_free(png_ptr, png_ptr->unknown_chunk.data);
+         png_ptr->unknown_chunk.data = NULL;
+       }
    }
    else
 #endif
       skip = length;
diff -ru4N libpng-1.2.26/pngset.c libpng-1.2.27beta01/pngset.c
--- libpng-1.2.26/pngset.c	2008-04-02 12:27:30.621225067 -0500
+++ libpng-1.2.27beta01/pngset.c	2008-04-05 21:41:15.248946598 -0500
@@ -1,8 +1,8 @@
 
 /* pngset.c - storage of image information into info struct
  *
- * Last changed in libpng 1.2.25 [February 18, 2008]
+ * Last changed in libpng 1.2.27 [April 6, 2008]
  * For conditions of distribution and use, see copyright notice in png.h
  * Copyright (c) 1998-2008 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
  * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
@@ -1039,30 +1039,33 @@
     info_ptr->unknown_chunks=NULL;
 
     for (i = 0; i < num_unknowns; i++)
     {
-        png_unknown_chunkp to = np + info_ptr->unknown_chunks_num + i;
-        png_unknown_chunkp from = unknowns + i;
+       png_unknown_chunkp to = np + info_ptr->unknown_chunks_num + i;
+       png_unknown_chunkp from = unknowns + i;
 
-        png_memcpy((png_charp)to->name, 
-                   (png_charp)from->name, 
-                   png_sizeof(from->name));
-        to->name[png_sizeof(to->name)-1] = '\0';
+       png_memcpy((png_charp)to->name, 
+                  (png_charp)from->name, 
+                  png_sizeof(from->name));
+       to->name[png_sizeof(to->name)-1] = '\0';
+       to->size = from->size;
+       /* note our location in the read or write sequence */
+       to->location = (png_byte)(png_ptr->mode & 0xff);
 
-        to->data = (png_bytep)png_malloc_warn(png_ptr, from->size);
-        if (to->data == NULL)
-        {
-           png_warning(png_ptr,
+       if (from->size == 0)
+          to->data=NULL;
+       else
+       {
+          to->data = (png_bytep)png_malloc_warn(png_ptr, from->size);
+          if (to->data == NULL)
+          {
+             png_warning(png_ptr,
               "Out of memory while processing unknown chunk.");
-        }
-        else
-        {
-           png_memcpy(to->data, from->data, from->size);
-           to->size = from->size;
-
-           /* note our location in the read or write sequence */
-           to->location = (png_byte)(png_ptr->mode & 0xff);
-        }
+             to->size=0;
+          }
+          else
+             png_memcpy(to->data, from->data, from->size);
+       }
     }
 
     info_ptr->unknown_chunks = np;
     info_ptr->unknown_chunks_num += num_unknowns;
diff -ru4N libpng-1.2.26/pngwrite.c libpng-1.2.27beta01/pngwrite.c
--- libpng-1.2.26/pngwrite.c	2008-04-02 12:27:30.775542734 -0500
+++ libpng-1.2.27beta01/pngwrite.c	2008-04-05 21:41:15.402698604 -0500
@@ -111,8 +111,10 @@
             !(up->location & PNG_HAVE_IDAT) &&
             ((up->name[3] & 0x20) || keep == PNG_HANDLE_CHUNK_ALWAYS ||
             (png_ptr->flags & PNG_FLAG_KEEP_UNSAFE_CHUNKS)))
          {
+            if (up->size == 0)
+               png_warning(png_ptr, "Writing zero-length unknown chunk");
             png_write_chunk(png_ptr, up->name, up->data, up->size);
          }
        }
    }