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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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