X.Org security advisory, June 3rd, 2008
Multiple vulnerabilities in X server extensions
CVE IDs: CVE-2008-1377, CVE-2008-1379,  CVE-2008-2360, CVE-2008-2361, 
         CVE-2008-2362

Overview

Several vulnerabilities have been found in the server-side code 
of some extensions in the X Window System. Improper validation of
client-provided data can cause data corruption.

Impact

Exploiting these overflows will crash the X server or,
under certain circumstances allow the execution of arbitray machine code.

When the X server is running with root privileges (which is the case
for the Xorg server and for most kdrive based servers), these
vulnerabilities can thus also be used to raise privileges.

All these vulnerabilities, to be exploited succesfully, require either
an already established connection to a running X server (and normally
running X servers are only accepting authenticated connections), or a
shell access with a valid user on the machine where the vulnerable
server is installed.

Affected versions

All released X.Org versions are vulnerable to these problems. Other
implementations derived from the X11 sample implementation are likely
to be affected too.


Vulnerabilities details

 * CVE-2008-2360 - RENDER Extension heap buffer overflow

An integer overflow may occur in the computation of the size of the
glyph to be allocated by the AllocateGlyph() function which will cause
less memory to be allocated than expected, leading to later heap
overflow.

On systems where the X  SIGSEGV handler includes a stack trace, more
malloc()-type functions are called, which may lead to other
exploitable issues. 

 * CVE-2008-2361 - RENDER Extension crash

Similarly, an integer overflow may occur in the computation of the
size of the  glyph to be allocated by the PRocRenderCreateCursor()
function  which will cause less memory to be allocated than expected,
leading later to dereferencing  un-mapped memory, causing a crash of
the X server.

 * CVE-2008-2362 - RENDER Extension memory corruption 

Integer overflows can also occur in the code validating the parameters
for the SProcRenderCreateLinearGradient, SProcRenderCreateRadialGradient and
SProcRenderCreateConicalGradient functions, leading to memory
corruption by swapping bytes outside of the intended request
parameters. 

 * CVE-2008-1379 - MIT-SHM arbitrary memory read

An integer overflow in the validation of the parameters of the
ShmPutImage() request makes it possible to trigger the copy of
arbitrary server memory to a pixmap that can subsequently be read by
the client, to read arbitrary parts of the X server memory space.

 * CVE-2008-1377 - RECORD and Security extensions memory corruption

Lack of validation of the parameters of the 
SProcSecurityGenerateAuthorization SProcRecordCreateContext 
functions makes it possible for a specially crafted request to trigger
the swapping of bytes outside the parameter of these requests, causing
memory corruption.

 * DBE Memory corruption 

There is a bit of broken program logic in DBE code. After calling
XdbeAllocateBackBufferName() (dbe/dbe.c, line 365) with 'drawable' being an
oversized Window resource (big enough to make CreatePixmap() fail)
DbeWindowPriv (pWindow->devPrivates[dbeWindowPrivIndex].ptr) is left in
inconsistent state, leading to potential X server crash, but without
exploitable conditions.

Workarounds

The vulnerabilies described here can be avoided by disabling the
corresponding extensions (at the cost of losing the functionalities
offered by these extensions) in the /etc/X11/xorg.conf configuration
file:


  Section "Extensions"   
	Option "MIT-SHM" "disable"
	Option "RENDER" "disable" 
	Option "SECURITY" "disable"
  EndSection

  Section "Module"
       Disable "record"
  EndSection

Fixes 

Fixes for all these vulnerabilities will be included in the next
release of the Xorg xserver package. Patches for earlier versions are
also provided:

ftp://ftp.freedesktop.org/pub/xorg/X11R7.2/patches/

ftp://ftp.freedesktop.org/pub/xorg/X11R7.3/patches/

Credits

These vulnerabilities were reported to iDefense by regenrecht.