Several vulnerabilities were discovered by blexim(at)hush.com in the font libraries of XFree86 version 4.3.0 and earlier. These bugs could potentially lead to execution of arbitrary code or a DoS by a remote user in any way that calls these functions, which are related to the transfer and enumeration of fonts from font servers to clients.

As well, some bugs were fixed in XFree86 as released with Mandrake Linux 9.2, specifically a problem where X would freeze with a black screen at logout or shutdown with DRI enabled on certain ATI Radeon cards.

#use wml::fmt::verbatim

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 provide security fixes to font libraries and XDM.

XFree86 is an implementation of the X Window System providing the core graphical user interface and video drivers. XDM is the X display manager.

Multiple integer overflows in the transfer and enumeration of font libraries in 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. The Common Vulnerabilities and Exposures project (cve.mitre.org) has assigned the name CVE-2003-0730 to this issue.

The risk to users from this vulnerability is limited because only clients can be affected by these bugs, however in some (non-default) configurations, both xfs and the X Server can act as clients to remote font servers.

XDM does not verify whether the pam_setcred function call succeeds, which may allow attackers to gain root privileges by triggering error conditions within PAM modules, as demonstrated in certain configurations of the pam_krb5 module. The Common Vulnerabilities and Exposures project (cve.mitre.org) has assigned the name CVE-2003-0690 to this issue.

Users are advised to upgrade to these updated XFree86 4.1.0 packages, which contain backported security patches and are not vulnerable to these issues.

ID	名稱	產品	系列	已發布	已更新	嚴重性
14071	Mandrake Linux Security Advisory : XFree86 (MDKSA-2003:089)	Nessus	Mandriva Local Security Checks	2004/7/31	2021/1/6	high
15217	Debian DSA-380-1 : xfree86 - buffer overflows, denial of service	Nessus	Debian Local Security Checks	2004/9/29	2021/1/4	high
12424	RHEL 2.1 : XFree86 (RHSA-2003:289)	Nessus	Red Hat Local Security Checks	2004/7/6	2021/1/14	critical

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