Multiple off-by-one errors in the (1) MakeBigReq and (2) SetReqLen macros in include/X11/Xlibint.h in X11R6.x and libX11 before 1.6.0 allow remote attackers to have unspecified impact via a crafted request, which triggers a buffer overflow.

The Xinput module (modules/im/ximcp/imLcIm.c) in X.Org libX11 1.0.2 and 1.0.3 opens a file for reading twice using the same file descriptor, which causes a file descriptor leak that allows local users to read files specified by the XCOMPOSEFILE environment variable via the duplicate file descriptor.