[NEWS] Mac OS X malloc() Local Privilege Escalation

From: SecuriTeam (support_at_securiteam.com)
Date: 09/29/05

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Date: 29 Sep 2005 11:06:14 +0200

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      Mac OS X malloc() Local Privilege Escalation
    ------------------------------------------------------------------------

    SUMMARY

    The Mac OS X malloc() function uses environment variables that can be
    modified by a local attacker and used to perform a privilege escalation
    attack.

    DETAILS

    Vulnerable Systems:
     * Mac OS X prior to Apple security update 2005-008

    The malloc() function within the libSystem library on Mac OS X uses
    several environment variables to enable various logging functionality. The
    description of one of these variables, "MallogLogFile" taken from the
    manual page is shown below:

           MallocLogFile <f> Create/append messages to the given
    file
                                         path <f> instead of writing to the
    standard
                                         error.

    An error exists in the fact that malloc() will still pay attention to this
    variable when an application is suid root.

    The following code taken from libSystem (libc) illustrates this:
    flag = getenv("MallocLogFile");
          if (flag) {
                 fd = open(flag, O_WRONLY|O_APPEND|O_CREAT, 0644);
                 if (fd >= 0) {
                       malloc_debug_file = fd;
                       fcntl(fd, F_SETFD, 0); // clear close-on-exec flag XXX
    why?
                 } else {
                       malloc_printf("Could not open %s, using stderr\n",
    flag);
                 }
          }

    A malicious user can set this variable before running a suid application
    in order to modify any file on the system. This can be used in order to
    trivially escalate privileges on the system.

    Vendor Status:
    The vendor has issued a fix to the issue in Security Update 2005-008.

    CVE Information:
     <http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2005-2748>
    CAN-2005-2748

    ADDITIONAL INFORMATION

    The information has been provided by <mailto:advisories@suresec.org>
    Suresec Advisories.
    The original article can be found at:
    <http://www.suresec.org/advisories/adv7.pdf>
    http://www.suresec.org/advisories/adv7.pdf

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