Vulnerability in the MIT-SHM extension of the X server on Linux (XFree86) 4.2.1 and earlier allows local users to read and write arbitrary shared memory, possibly to cause a denial of service or gain privileges.

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Four vulnerabilities have been discovered in XFree86.

  - CAN-2003-0063- xterm window title reporting escape     sequence can deceive user     The xterm package provides a terminal escape sequence     that reports the window title by injecting it into the     input buffer of the terminal window, as if the user had     typed it. An attacker can craft an escape sequence that     sets the title of a victim's xterm window to an     arbitrary string (such as a shell command) and then     reports that title. If the victim is at a shell prompt     when this is done, the injected command will appear on     the command line, ready to be run. Since it is not     possible to embed a carriage return in the window title,     the attacker would have to convince the victim to press     Enter (or rely upon the victim's careless or confusion)     for the shell or other interactive process to interpret     the window title as user input. It is conceivable that     the attacker could craft other escape sequences that     might convince the victim to accept the injected input,     however. The Common Vulnerabilities and Exposures     project at cve.mitre.org has assigned the name     CAN-2003-0063 to this issue.

  To determine whether your version of xterm is vulnerable to abuse of   the window title reporting feature, run the following command at a   shell prompt from within an xterm window :

    echo -e '\e[21t'

  (The terminal bell may ring, and the window title may be prefixed   with an 'l'.)

  This flaw is exploitable by anything that can send output to a   terminal window, such as a text document. The xterm user has to take   action to cause the escape sequence to be sent, however (such as by   viewing a malicious text document with the 'cat' command). Whether   you are likely to be exposed to it depends on how you use xterm.
  Consider the following :

    echo -e '\e]2;s && echo rm -rf *\a' > /tmp/sploit echo -e '\e[21t'     >> /tmp/sploit cat /tmp/sploit

  Debian has resolved this problem by disabling the window title   reporting escape sequence in xterm; it is understood but ignored.
  The escape sequence to set the window title has not been disabled.

  A future release of the xterm package will have a configuration   option to permit the user to turn the window title reporting feature   back on, but it will default off.

  - CAN-2003-0071- xterm susceptible to DEC UDK escape     sequence denial-of-service attack

    The xterm package, since it emulates DEC VT-series text     terminals, emulates a feature of DEC VT terminals known     as 'User-Defined Keys' (UDK for short). There is a bug     in xterm's handling of DEC UDK escape sequences,     however, and an ill-formed one can cause the xterm     process to enter a tight loop. This causes the process     to 'spin', consuming CPU cycles uselessly, and refusing     to handle signals (such as efforts to kill the process     or close the window).

  To determine whether your version of xterm is vulnerable to this   attack, run the following command at a shell prompt from within a   'sacrificial' xterm window (i.e., one that doesn't have anything in   the scrollback buffer you might need to see later) :

    echo -e '\eP0;0|0A/17\x9c'

  This flaw is exploitable by anything that can send output to a   terminal window, such as a text document. The xterm user has to take   action to cause the escape sequence to be sent, however (such as by   viewing a malicious text document with the 'cat' command). Whether   you are likely to be exposed to it depends on how you use xterm.

  Debian has resolved this problem by backporting an upstream fix to   XFree86 4.1.0.

  - CAN-2002-0164- flaw in X server's MIT-SHM extension     permits user owning X session to read and write     arbitrary shared memory segments

    Most X servers descended from the MIT/X Consortium/X.Org     Sample Implementation, including XFree86's X servers,     support an extension to the X protocol called MIT-SHM,     which enables X clients running on the same host as the     X server to operate more quickly and efficiently by     taking advantage of an operating system feature called     shared memory where it is available. The Linux kernel,     for example, supports shared memory.

  Because the X server runs with elevated privileges, the operating   system's built-in access control mechanisms are ineffective to   police the X server's usage of segments of shared memory. The X   server has to implement its own access control. This was imperfectly   done in previous releases of XFree86 (and the MIT/X Consortium/X.Org   Sample Implementation before it), leaving opportunities for   malicious X clients to read and alter shared memory segments to   which they should not have access. The Common Vulnerabilities and   Exposures project at cve.mitre.org has assigned the name   CAN-2002-0164 to this issue.

  Debian's XFree86 4.1.0-16 packages shipped with an incomplete fix   for the this flaw, only enforcing proper access control for X   servers that were not started by a display manager (e.g., xdm). This   update resolves that problem.

  The Debian Project knows of no exploits for this vulnerability. A   malicious X client that abused the MIT-SHM extension could   conceivably be written however, and run (deliberately or   unwittingly) by a user able to run an X server on a host. The impact   of this flaw depends on how shared memory is used on the system. See   the ipcs(8) manual page for more information.

  Debian has resolved this problem by backporting an upstream fix to   XFree86 4.1.0.

  - CAN-2003-0730- multiple integer overflows in the font     libraries for XFree86 allow local or remote attackers to     cause a denial of service or execute arbitrary code via     heap-based and stack-based buffer overflow attacks

    Security researcher 'blexim' wrote [paraphrased] :

    I have identified several bugs in the font libraries of the     current version of the XFree86 source code. These bugs could     potentially lead to the execution of arbitrary code by a remote     user in any process which calls the functions in question. The     functions are related to the transfer and enumeration of fonts     from font servers to clients, limiting the range of the exposure     caused by these bugs.

    Specifically, several sizing variables passed from a font server     to a client are not adequately checked, causing calculations on     them to result in erroneous values. These erroneous calculations     can lead to buffers on the heap and stack overflowing, potentially     leading to arbitrary code execution. As stated before, the risk is     limited by the fact that only clients can be affected by these     bugs, but in some (non-default) configurations, both xfs and the X     server can act as clients to remote font servers. In these     configurations, both xfs and the X server could be potentially     compromised.

  The Common Vulnerabilities and Exposures project at cve.mitre.org   has assigned the name CAN-2003-0730 to this issue.

  The Debian Project knows of no exploits for this vulnerability. By   default in Debian, X servers are configured to listen only to a   locally-running font server, which is not even used if the xfs   package is not installed. The Debian default configuration of xfs   uses only font directories on the local host, and does not attempt   to connect to any external font servers.

  Debian has resolved this problem by backporting an upstream fix to   XFree86 4.1.0.

All of the above problems also affect the xfree86v3 packages (in the case of the first two flaws, the xterm source code contains the flaws, but no xterm package is produced). Due to resource limitations and a lack of upstream support for this legacy code, Debian is unable to continue supporting version 3.3.6 of XFree86. To avoid exposure to the latter two flaws in this advisory, we recommend that you remove the following packages if you have them installed :

  - xserver-3dlabs
  - xserver-8514

  - xserver-agx

  - xserver-common-v3

  - xserver-fbdev

  - xserver-i128

  - xserver-mach32

  - xserver-mach64

  - xserver-mach8

  - xserver-mono

  - xserver-p9000

  - xserver-s3

  - xserver-s3v

  - xserver-svga

  - xserver-tga

  - xserver-vga16

  - xserver-w32

(You may also wish to remove the xext, xlib6, and xlib6-altdev packages, as support for them is being terminated along with the rest of the XFree86 3.3.6 packages, though they are not affected by the flaws in this advisory.)

Updated XFree86 packages that resolve various security issues and additionally provide a number of bug fixes and enhancements are now available for Red Hat Enterprise Linux 2.1.

XFree86 is an implementation of the X Window System, which provides the graphical user interface, video drivers, etc. for Linux systems.

A number of security vulnerabilities have been found and fixed. In addition, various other bug fixes, driver updates, and other enhancements have been made.

Security fixes :

Xterm, provided as part of the XFree86 packages, provides an escape sequence for reporting the current window title. This escape sequence essentially takes the current title and places it directly on the command line. An attacker can craft an escape sequence that sets the victim's Xterm window title to an arbitrary command, and then reports it to the command line. Since it is not possible to embed a carriage return into the window title, the attacker would then have to convince the victim to press Enter for the shell to process the title as a command, although the attacker could craft other escape sequences that might convince the victim to do so. The Common Vulnerabilities and Exposures project (cve.mitre.org) has assigned the name CVE-2003-0063 to this issue.

It is possible to lock up versions of Xterm by sending an invalid DEC UDK escape sequence. The Common Vulnerabilities and Exposures project (cve.mitre.org) has assigned the name CVE-2003-0071 to this issue.

The xdm display manager, with the authComplain variable set to false, allows arbitrary attackers to connect to the X server if the xdm auth directory does not exist. The Common Vulnerabilities and Exposures project (cve.mitre.org) has assigned the name CVE-2002-1510 to this issue.

These erratum packages also contain an updated fix for CVE-2002-0164, a vulnerability in the MIT-SHM extension of the X server that allows local users to read and write arbitrary shared memory. The original fix did not cover the case where the X server is started from xdm.

The X server was setting the /dev/dri directory permissions incorrectly, which resulted in the directory being world-writable. It now sets the directory permissions to a safe value. The Common Vulnerabilities and Exposures project (cve.mitre.org) has assigned the name CVE-2001-1409 to this issue.

Driver updates and other fixes :

The Rage 128 video driver (r128) has been updated to provide 2D support for all previously unsupported ATI Rage 128 hardware. DRI 3D support should also work on the majority of Rage 128 hardware.

Bad page size assumptions in the ATI Radeon video driver (radeon) have been fixed, allowing the driver to work properly on ia64 and other architectures where the page size is not fixed.

A long-standing XFree86 bug has been fixed. This bug occurs when any form of system clock skew (such as NTP clock synchronization, APM suspend/resume cycling on laptops, daylight savings time changeover, or even manually setting the system clock forward or backward) could result in odd application behavior, mouse and keyboard lockups, or even an X server hang or crash.

The S3 Savage driver (savage) has been updated to the upstream author's latest version '1.1.27t', which should fix numerous bugs reported by various users, as well as adding support for some newer savage hardware.

Users are advised to upgrade to these updated packages, which contain XFree86 version 4.1.0 with patches correcting these issues.

According to its telnet banner, the remote host is a SCO Unix server running OpenServer version 5.0.5, 5.0.6, or 5.0.7.  Such versions are vulnerable to two distinct exploits.  Namely,

  - Xsco can be locally exploited by any valid user in     order to escalate their privileges to 'root'.  The bug     is due to improper input handling when running the     command line switch '-co'.

  - There is a vulnerability in the MIT-SHM extension within     all X servers that are running as root.  Any user with     local X access can exploit the MIT-SHM extension and     gain read/write access to any shared memory segment on     the system.

ID	Name	Product	Family	Severity
15217	Debian DSA-380-1 : xfree86 - buffer overflows, denial of service	Nessus	Debian Local Security Checks	high
12369	RHEL 2.1 : XFree86 (RHSA-2003:065)	Nessus	Red Hat Local Security Checks	critical
11895	SCO OpenServer Multiple Local Privilege Escalation Vulnerabilities	Nessus	Misc.	high

Detections

Analytics

CVE-2002-0164

high

Tenable Plugins

high

critical

high