CVE 2007-6429
Multiple integer overflows in X.Org Xserver before 1.4.1 allow context-dependent attackers to execute arbitrary code via (1) a GetVisualInfo request containing a 32-bit value that is improperly used to calculate an amount of memory for allocation by the EVI extension, or (2) a request containing values related to pixmap size that are improperly used in management of shared memory by the MIT-SHM extension.
See the 
CVE page on Mitre.org
for more details.
