Buffer overflow in the compNewPixmap function in compalloc.c in the Composite extension for the X.org X11 server before 1.4 allows local users to execute arbitrary code by copying data from a large pixel depth pixmap into a smaller pixel depth pixmap.

X.Org and XFree86, including libX11, xdm, xf86dga, xinit, xload, xtrans, and xterm, does not check the return values for setuid and seteuid calls when attempting to drop privileges, which might allow local users to gain privileges by causing those calls to fail, such as by exceeding a ulimit.