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)". A vulnerability exists in Graphviz's parsing engine which makes it possible to overflow a globally allocated array and corrupt memory by doing so.
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.
Solution:
A bounds check has been added in order to avoid an overflow, it can be seen in the parser.y file (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: }
