X.Org Security Advisory: Dec. 9, 2014

Protocol handling issues in X Window System servers


Ilja van Sprundel, a security researcher with IOActive, has discovered a large number of issues in the way the X server code base handles requests from X clients, and has worked with X.Org's security team to analyze, confirm, and fix these issues.

Ilja's talk at the 30th Chaos Communication Congress (30C3) in Hamburg last year (X Security: it's worse than it looks) gave a preview of these issues and discussed the general form of many of these, but did not disclose the exact details of them.

The vulnerabilities could be exploited to cause the X server to access uninitialized memory or overwrite arbitrary memory in the X server process. This can cause a denial of service (e.g., an X server segmentation fault), or could be exploited to achieve arbitrary code execution.

How critical these vulnerabilities are to any given installation depends on whether they run an X server with root privileges or reduced privileges; whether they run X servers exposed to network clients or limited to local connections; and whether or not they allow use of the affected protocol extensions, especially the GLX extension.

The GLX extension to the X Window System allows an X client to send X protocol to the X server, to request that the X server perform OpenGL rendering on behalf of the X client. This is known as “GLX indirect rendering”, as opposed to “GLX direct rendering” where the X client submits OpenGL rendering commands directly to the GPU, bypassing the X server and avoiding the X server code for GLX protocol handling.

Most GLX indirect rendering implementations share some common ancestry, dating back to “Sample Implementation” code from Silicon Graphics, Inc (SGI), which SGI originally commercially licensed to other Unix workstation and graphics vendors, and later released as open source, so those vulnerabilities may affect other licensees of SGI's code base beyond those running code from the X.Org Foundation or the XFree86 Project.

The vulnerabilities include:

denial of service due to unchecked malloc in client authentication

CVE-2014-8091: In servers built with support for SUN-DES-1 (Secure RPC) authentication credentials, an unauthenticated client may be able to crash the X server by sending a connection request specifying values that cause malloc to fail, causing the authentication routines to attempt to write data to the returned NULL pointer. Since the request is limited to an unsigned 16-bit integer for the allocation size, it is unlikely to fail unless the server is severely memory constrained.

Introduced in the initial revision of Secure RPC support in X11R5 (1991).

integer overflows calculating memory needs for requests

These calls do not check that their calculations for how much memory is needed to handle the client's request have not overflowed, so can result in out of bounds reads or writes. These calls all occur only after a client has successfully authenticated itself.

CVE-2014-8092: X11 core protocol requests

Affected functions: ProcPutImage(), GetHosts(), RegionSizeof(), REQUEST_FIXED_SIZE()

Introduced in X11R1 (1987).

CVE-2014-8093: GLX extension

Affected functions: __glXDisp_ReadPixels(), __glXDispSwap_ReadPixels(), __glXDisp_GetTexImage(), __glXDispSwap_GetTexImage(), GetSeparableFilter(), GetConvolutionFilter(), GetHistogram(), GetMinmax(), GetColorTable(), __glXGetAnswerBuffer(), __GLX_GET_ANSWER_BUFFER(), __glXMap1dReqSize(), __glXMap1fReqSize(), Map2Size(), __glXMap2dReqSize(), __glXMap2fReqSize(), __glXImageSize(), __glXSeparableFilter2DReqSize()

Originally developed by SGI and licensed to multiple vendors prior to SGI open sourcing the code in 1999.
Included in XFree86 releases starting in XFree86 4.0 (2000).
Included in X.Org releases starting in X11R6.7 (2004).

CVE-2014-8094: DRI2 extension

Affected functions: ProcDRI2GetBuffers()

Introduced in xorg-server-1.7.0 (2009).

out of bounds access due to not validating length or offset values in requests

These calls do not check that the lengths and/or indexes sent by the client are within the bounds specified by the caller or the bounds of the memory allocated to hold the request read from the client, so could read or write past the bounds of allocated memory while processing the request. These calls all occur only after a client has successfully authenticated itself.

CVE-2014-8095: XInput extension

Affected functions: SProcXChangeDeviceControl(), ProcXChangeDeviceControl(), ProcXChangeFeedbackControl(), ProcXSendExtensionEvent(), SProcXIAllowEvents(), SProcXIChangeCursor(), ProcXIChangeHierarchy(), SProcXIGetClientPointer(), SProcXIGrabDevice(), SProcXIUngrabDevice(), ProcXIUngrabDevice(), SProcXIPassiveGrabDevice(), ProcXIPassiveGrabDevice(), SProcXIPassiveUngrabDevice(), ProcXIPassiveUngrabDevice(), SProcXListDeviceProperties(), SProcXDeleteDeviceProperty(), SProcXIListProperties(), SProcXIDeleteProperty(), SProcXIGetProperty(), SProcXIQueryDevice(), SProcXIQueryPointer(), SProcXISelectEvents(), SProcXISetClientPointer(), SProcXISetFocus(), SProcXIGetFocus(), SProcXIWarpPointer()

Introduced in X11R4 (1989).

CVE-2014-8096: XC-MISC extension

Affected functions: SProcXCMiscGetXIDList()

Introduced in X11R6.0 (1994).

CVE-2014-8097: DBE extension

Affected functions: ProcDbeSwapBuffers(), SProcDbeSwapBuffers()

Introduced in X11R6.1 (1996).

CVE-2014-8098: GLX extension

Affected functions: __glXDisp_Render(), __glXDisp_RenderLarge(), __glXDispSwap_VendorPrivate(), __glXDispSwap_VendorPrivateWithReply(), set_client_info(), __glXDispSwap_SetClientInfoARB(), DoSwapInterval(), DoGetProgramString(), DoGetString(), __glXDispSwap_RenderMode(), __glXDisp_GetCompressedTexImage(), __glXDispSwap_GetCompressedTexImage(), __glXDisp_FeedbackBuffer(), __glXDispSwap_FeedbackBuffer(), __glXDisp_SelectBuffer(), __glXDispSwap_SelectBuffer(), __glXDisp_Flush(), __glXDispSwap_Flush(), __glXDisp_Finish(), __glXDispSwap_Finish(), __glXDisp_ReadPixels(), __glXDispSwap_ReadPixels(), __glXDisp_GetTexImage(), __glXDispSwap_GetTexImage(), __glXDisp_GetPolygonStipple(), __glXDispSwap_GetPolygonStipple(), __glXDisp_GetSeparableFilter(), __glXDisp_GetSeparableFilterEXT(), __glXDisp_GetConvolutionFilter(), __glXDisp_GetConvolutionFilterEXT(), __glXDisp_GetHistogram(), __glXDisp_GetHistogramEXT(), __glXDisp_GetMinmax(), __glXDisp_GetMinmaxEXT(), __glXDisp_GetColorTable(), __glXDisp_GetColorTableSGI(), GetSeparableFilter(), GetConvolutionFilter(), GetHistogram(), GetMinmax(), GetColorTable()

Originally developed by SGI and licensed to multiple vendors prior to SGI open sourcing the code in 1999.
Included in XFree86 releases starting in XFree86 4.0 (2000).
Included in X.Org releases starting in X11R6.7 (2004).

CVE-2014-8099: XVideo extension

Affected functions: SProcXvQueryExtension(), SProcXvQueryAdaptors(), SProcXvQueryEncodings(), SProcXvGrabPort(), SProcXvUngrabPort(), SProcXvPutVideo(), SProcXvPutStill(), SProcXvGetVideo(), SProcXvGetStill(), SProcXvPutImage(), SProcXvShmPutImage(), SProcXvSelectVideoNotify(), SProcXvSelectPortNotify(), SProcXvStopVideo(), SProcXvSetPortAttribute(), SProcXvGetPortAttribute(), SProcXvQueryBestSize(), SProcXvQueryPortAttributes(), SProcXvQueryImageAttributes(), SProcXvListImageFormats()

Introduced in XFree86 4.0.0 (2000).
Included in X.Org releases starting in X11R6.7 (2004).

CVE-2014-8100: Render extension

Affected functions: ProcRenderQueryVersion(), SProcRenderQueryVersion(), SProcRenderQueryPictFormats(), SProcRenderQueryPictIndexValues(), SProcRenderCreatePicture(), SProcRenderChangePicture(), SProcRenderSetPictureClipRectangles(), SProcRenderFreePicture(), SProcRenderComposite(), SProcRenderScale(), SProcRenderCreateGlyphSet(), SProcRenderReferenceGlyphSet(), SProcRenderFreeGlyphSet(), SProcRenderFreeGlyphs(), SProcRenderCompositeGlyphs()

Introduced in XFree86 4.0.1 (2000).
Included in X.Org releases starting in X11R6.7 (2004).

CVE-2014-8101: RandR extension

Affected functions: SProcRRQueryVersion(), SProcRRGetScreenInfo(), SProcRRSelectInput(), SProcRRConfigureOutputProperty()

Introduced in XFree86 4.2.0 (2002).
Included in X.Org releases starting in X11R6.7 (2004).

CVE-2014-8102: XFixes extension

Affected functions: SProcXFixesSelectSelectionInput()

Introduced in X11R6.8.0 (2004).

CVE-2014-8103: DRI3 & Present extensions

Affected functions: sproc_dri3_query_version(), sproc_dri3_open(), sproc_dri3_pixmap_from_buffer(), sproc_dri3_buffer_from_pixmap(), sproc_dri3_fence_from_fd(), sproc_dri3_fd_from_fence(), proc_present_query_capabilities(), sproc_present_query_version(), sproc_present_pixmap(), sproc_present_notify_msc(), sproc_present_select_input(), sproc_present_query_capabilities()

Introduced in xorg-server-1.15.0 (2013).

Affected Versions

X.Org believes all versions of the affected functions contain these flaws, dating back to their introduction. In the above listings, we've listed the earliest date of any of the affected functions in a given protocol or area - some functions listed may not have been introduced until later versions.


Fixes are available in these git commits:

Note that many of these patches depend on being applied in the same order as they are in git, or on other non-CVE patches in git, and won't necessarily apply as is to previous tarball releases.

Fixes are also planned to be included in the xorg-server-1.17.0 and xorg-server-1.16.3 releases.

Other providers of Xserver or GLX implementations based on the same code base (the X Consortium or X.Org Foundation X sources, or the SGI GLX sources) will announce the availability of any fixes necessary for their implementations.


While the fixes cover all the cases currently known to X.Org, these are not the first issues in this area and are unlikely to be the last.

Users can reduce their exposure to issues similar to the ones in this advisory via these methods:

  • Configure the X server to prohibit X connections from the network by passing the -nolisten tcp command line option to the X server. Many OS distributions already set this option by default, and it will be set by default in the upstream X.Org release starting with Xorg 1.17.

  • Disable GLX indirect contexts. Some implementations have a configuration option for this. In Xorg 1.16 or newer, this can be achieved by setting the -iglx X server command line option. This option will be the default in Xorg 1.17 and later releases.

Consult your operating system's documentation for details on setting X server command line options, as X servers are started by a variety of different methods on different platforms (startx, gdm, kdm, xdm, etc.).


X.Org thanks Ilja van Sprundel of IOActive for reporting these issues to our security team and assisting them in understanding them and evaluating our fixes, and the following X.Org contributors for developing and reviewing the fixes, tests, and advisory for these issues, and coordinating the X.Org response to them:

  • Adam Jackson (Red Hat)
  • Alan Coopersmith (Oracle)
  • Andy Ritger (NVIDIA)
  • Julien Cristau (Debian)
  • Keith Packard (Intel)
  • Michal Srb (SuSE)
  • Peter Hutterer (Red Hat)
  • Robert Morell (NVIDIA)