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Stunnel Secure Tunneling Program Format String Flaw Allows Remote Malicious Stunnel Servers to Crash the Tunnel and May Allow Remote Malicious Servers to Execute Arbitrary Commands on the Peer Host
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SecurityTracker Alert ID: 1003064 |
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SecurityTracker URL: http://securitytracker.com/id/1003064
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CVE Reference:
GENERIC-MAP-NOMATCH
(Links to External Site)
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Date: Dec 27 2001
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Impact:
Denial of service via network, Execution of arbitrary code via network
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Fix Available: Yes Vendor Confirmed: Yes Exploit Included: Yes
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Version(s): stunnel-3.21c and prior
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Description:
A format string vulnerability was reported in Stunnel connection tunneling program. A remote server that is part of an stunnel can cause the stunnel to crash and may be able to execute arbitrary commands on the remote client.
EnGarde reported that there is a format string vulnerability in stunnel that may allow a remote user to impersonate a valid server and crash the tunnel or cause arbitrary code to be executed on the client host originating an stunnel connection.
Engarde reports that it has not been confirmed whether this is exploitable or not and also credits Matthias Lange for originally reporting this on the stunnel-users mailing list.
It is reported that an stunnel can be crashed in the following configuration:
Acting as a mail server:
$ netcat -p 252525 -l
Acting as a mail client:
$ stunnel -c -n smtp -r localhost:252525
When the connection is established, a user can send a string such as
"%s%s%s%s%s%s%s%s%s%s%s%s" from netcat to the stunnel to cause the stunnel to crash. This is reportedly due to stunnel performing fdprintf(c->local_wfd,"%s%s%s%s...") and then crashing.
The vendor reports that the format string bug exists in the protocol.c file and the smtp, pop3, and nntp services in client mode are affected.
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Impact:
A remote user acting as an stunnel server can cause an stunnel connection to crash and may be able to cause arbitrary code to be executed on the client host at the other end of the stunnel connection (however, remote code execution has not been confirmed).
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Solution:
The vendor has released a fixed version (3.22), available at the Vendor URL.
A user has provided a patch for stunnel-3.21c, available in an e-mail message:
http://marc.theaimsgroup.com/?l=stunnel-users&m=100868569203440&w=3
For EnGarde Secure Linux 1.0.1 (Finestra) users, the following packages are available:
Source packages:
SRPMS/stunnel-3.22-1.0.4.src.rpm
MD5 Sum: e408662d6fc54f3979642c9e8c110ba4
Binary Packages:
i386/stunnel-3.22-1.0.4.i386.rpm
MD5 Sum: 482ff9210541d73b114404ccb9732cf0
i686/stunnel-3.22-1.0.4.i686.rpm
MD5 Sum: afad91053b8d482e36e85251fab06755
Before upgrading the EnGarde Secure Linux package, the machine must either:
a) be booted into a "standard" kernel; or
b) have LIDS disabled.
To disable LIDS, execute the command:
# /sbin/lidsadm -S -- -LIDS_GLOBAL
To install the updated package, execute the command:
# rpm -Uvh <filename>
You must now update the LIDS configuration by executing the command:
# /usr/sbin/config_lids.pl
To re-enable LIDS (if it was disabled), execute the command:
# /sbin/lidsadm -S -- +LIDS_GLOBAL
To verify the signatures of the updated packages, execute the command:
# rpm -Kv <filename>
For other Linux distributions, check the Message History to see if any additional alerts have been posted.
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Vendor URL: www.stunnel.org/ (Links to External Site)
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Cause:
Input validation error
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Underlying OS:
Linux (Any), UNIX (Any), Windows (Any)
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Message History:
This archive entry has one or more follow-up message(s) listed below.
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Source Message Contents
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Date: Thu, 27 Dec 2001 11:18:53 -0500 (EST)
Subject: [ESA-20011227-01] stunnel format string vulnerability
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-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
+------------------------------------------------------------------------+
| EnGarde Secure Linux Security Advisory December 27, 2001 |
| http://www.engardelinux.org/ ESA-20011227-01 |
| |
| Package: stunnel |
| Summary: There is a format string vulnerability in stunnel. |
+------------------------------------------------------------------------+
EnGarde Secure Linux is a secure distribution of Linux that features
improved access control, host and network intrusion detection, Web
based secure remote management, complete e-commerce using AllCommerce,
and integrated open source security tools.
OVERVIEW
- --------
There is a format string vulnerability in stunnel which may allow an
attacker to exploit a victim by impersonating a mail server.
DETAIL
- ------
There are a couple of instances in stunnel where a format is not passed
to a printf-like function, leading to your classic format string
vulnerability. It is not know weather or not it is exploitable at this
time but all users are recommended to upgrade in any event.
This vulnerability was disclosed on December 18 by Matthias Lange on
the stunnel-users mailing list. The original message may be found here:
http://marc.theaimsgroup.com/?l=stunnel-users&m=100868569203440&w=3
All users should upgrade to the most recent version, as outlined in
SOLUTION
- --------
All users should upgrade to the most recent version as outlined in
this advisory. All updates may be found at:
ftp://ftp.engardelinux.org/pub/engarde/stable/updates/
http://ftp.engardelinux.org/pub/engarde/stable/updates/
Before upgrading the package, the machine must either:
a) be booted into a "standard" kernel; or
b) have LIDS disabled.
To disable LIDS, execute the command:
# /sbin/lidsadm -S -- -LIDS_GLOBAL
To install the updated package, execute the command:
# rpm -Uvh <filename>
You must now update the LIDS configuration by executing the command:
# /usr/sbin/config_lids.pl
To re-enable LIDS (if it was disabled), execute the command:
# /sbin/lidsadm -S -- +LIDS_GLOBAL
To verify the signatures of the updated packages, execute the command:
# rpm -Kv <filename>
UPDATED PACKAGES
- ----------------
These updated packages are for EnGarde Secure Linux 1.0.1 (Finestra).
Source Packages:
SRPMS/stunnel-3.22-1.0.4.src.rpm
MD5 Sum: e408662d6fc54f3979642c9e8c110ba4
Binary Packages:
i386/stunnel-3.22-1.0.4.i386.rpm
MD5 Sum: 482ff9210541d73b114404ccb9732cf0
i686/stunnel-3.22-1.0.4.i686.rpm
MD5 Sum: afad91053b8d482e36e85251fab06755
REFERENCES
- ----------
Guardian Digital's public key:
http://ftp.engardelinux.org/pub/engarde/ENGARDE-GPG-KEY
Credit for the discovery of this bug goes to:
Matthias Lange <ml@netuse.de>
stunnel's Official Web Site:
http://stunnel.mirt.net/
Security Contact: security@guardiandigital.com
EnGarde Advisories: http://www.engardelinux.org/advisories.html
- --------------------------------------------------------------------------
$Id: ESA-2001122701-stunnel,v 1.2 2001/12/27 16:02:00 rwm Exp $
- --------------------------------------------------------------------------
Author: Ryan W. Maple, <ryan@guardiandigital.com>
Copyright 2001, Guardian Digital, Inc.
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.0.6 (GNU/Linux)
Comment: For info see http://www.gnupg.org
iD8DBQE8K0n1HD5cqd57fu0RAgGXAKCVsY0gY+WDXFODzXS4bT035Wn4aACgjDhW
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=0i8Q
-----END PGP SIGNATURE-----
------------------------------------------------------------------------
To unsubscribe email engarde-security-request@engardelinux.org
with "unsubscribe" in the subject of the message.
Copyright(c) 2001 Guardian Digital, Inc. EnGardeLinux.org
------------------------------------------------------------------------
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