gtk+-2.4.4 XPM image decoder parsing flaws
==========================================
  
Programs:          gtk+, and any programs which use gtk+ to decode XPM
files.
                   For example, Evolution.
Severity:          Compromise of account used to browse malicious XPM
file.
CAN identifier(s): CAN-2004-0782, CAN-2004-0783
  
This advisory lists code flaws discovered by inspection of the XPM parser
within the gtk+ code. Specifically, gtk+-2.4.4 was investigated.
  
Flaw 1. Heap-based overflow in pixbuf_create_from_xpm (io-xpm.c)

CAN-2004-0782
  name_buf = g_new (gchar, n_col * (cpp + 1));
  colors = g_new (XPMColor, n_col);

Here, n_col is an arbitrary integer value from the XPM. cpp is an
integer value
ranging from 1 to 31 from the XPM. By careful choice of values of
n_col and
cpp, integer overflow can occur on integer multiplication. This leads
to heap
buffers being allocated that cannot hold n_col elements, so a
subsequent heap
overflow occurs.

Demo XPM: http://scary.beasts.org/misc/gdk1.xpm                      
                                                                     
                              


Flaw 2. Subtle stack-based overflow in xpm_extract_color (io-xpm.c)
CAN-2004-0783

  gint space = 128;
  gchar word[128], color[128], current_color[128];
...
      if (color[0] != '\0') {
        strcat (color, " ");
[*]     space--;
      }                                                              
                                                                     
                              
      strncat (color, word, space);
      space -= MIN (space, strlen (word));
  
Here, an attempt is actually made to prevent overflow of the stack
buffers.
However, a logic error means one of the buffers can still be made to
overflow.
When "space" reaches 0, "space" can be sent to -1 by the line marked
with [*],
if the color string is broken up by whitespace. When "space" is -1, the
strncat() call is effectively morphed to a strcat() call, allowing
overflow of
the "color" buffer (probably into the "word" buffer, which may cause a
minor
inconvenience to exploitation. Note use of the word "minor" :-)

Demo XPM: http://scary.beasts.org/misc/gdk2.xpm                      
                                                                     
                              

  
CESA-2004-005 - rev 1
Chris Evans