The graphviz team has just released a patch to a critical security issue
I reported to them.
The following is the advisory (also available at
http://roeehay.blogspot.com/2008/10/graphviz-buffer-overflow-code-execution.html):
Background
==========
Graphviz is an open-source multi-platform graph visualization software. It
takes a description of graphs in a simple text format (DOT language), and
makes diagrams out of it in several useful formats (including SVG).
Description
===========
A vulnerability exists in Graphviz's parsing engine which makes it possible to
overflow a globally allocated array and corrupt memory by doing so.
parser.y (Graphviz 2.20.2):
34: static Agraph_t *Gstack[32];
35: static int GSP;
45: static void push_subg(Agraph_t *g)
46: {
47: G = Gstack[GSP++] = g;
48: }
As it can be seen, no bounds check is performed by the push_svg procedure,
allowing one to overflow Gstack by pushing more than 32 (Agraph_t *)
elements.
Impact/Severity
===============
A malicious user can achieve an arbitrary code execution by creating a
specially crafted DOT file and convince the victim to render it using Graphviz.
Affected versions
=================
Graphviz 2.20.2 is affected by this vulnerability. Older version are probably
affected as well.
Workaround
===========
Version 2.20.3 has been released in order to address this issue. A bounds check
has been added in order to avoid an overflow.
parser.y (Graphviz 2.20.3):
34: #define GSTACK_SIZE 64
35: static Agraph_t *Gstack[GSTACK_SIZE];
36: static int GSP;
45:
46: static void push_subg(Agraph_t *g)
47: {
48: if (GSP >= GSTACK_SIZE) {
49: agerr (AGERR, "Gstack overflow in graph parser\n"); exit(1);
50: }
51: G = Gstack[GSP++] = g;
52: }
Acknowledgements
================
I would like to thank the Graphviz team (Stephen C. North, John Ellson,
Emden R. Gansner and others) for their quick responses and fix (it took them
only a day since my disclosure to release a patch!).
