CVE 2013-1997
Multiple buffer overflows in X.org libX11 1.5.99.901 (1.6 RC1) and earlier allow X servers to cause a denial of service (crash) and possibly execute arbitrary code via crafted length or index values to the (1) XAllocColorCells, (2) _XkbReadGetDevi
See the
CVE page on Mitre.org
for more details.