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

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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:[email protected]> 
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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