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SEC Consult Vulnerability Lab Security Advisory < 20180704-2 >
=======================================================================
title: Privilege escalation via linux group manipulation
product: All ADB Broadband Gateways / Routers
(based on Epicentro platform)
vulnerable version: Hardware: ADB P.RG AV4202N, DV2210, VV2220, VV5522, etc.
fixed version: see "Solution" section below
CVE number: CVE-2018-13110
impact: critical
homepage: http://www.adbglobal.com
found: 2016-07-11
by: Stefan Viehböck (Office Vienna)
Johannes Greil (Office Vienna)
SEC Consult Vulnerability Lab

An integrated part of SEC Consult
Europe | Asia | North America

https://www.sec-consult.com
=======================================================================

Vendor description:
-------------------
"ADB creates and delivers the right solutions that enable our customers to
reduce integration and service delivery challenges to increase ARPU and reduce
churn. We combine ADB know-how and products with those from a number of third
party industry leaders to deliver complete solutions that benefit from
collaborative thinking and best in class technologies."

Source: https://www.adbglobal.com/about-adb/

"Founded in 1995, ADB initially focused on developing and marketing software
for digital TV processors and expanded its business to the design and
manufacture of digital TV equipment in 1997. The company sold its first set-top
box in 1997 and since then has been delivering a number of set-top boxes, and
Gateway devices, together with advanced software platforms. ADB has sold over
60 million devices worldwide to cable, satellite, IPTV and broadband operators.
ADB employs over 500 people, of which 70% are in engineering functions."

Source: https://en.wikipedia.org/wiki/Advanced_Digital_Broadcast

Business recommendation:
------------------------
By exploiting the group manipulation vulnerability on affected and unpatched
devices an attacker is able to gain access to the command line interface (CLI)
if previously disabled by the ISP.

Depending on the feature-set of the CLI (ISP dependent) it is then possible to
gain access to the whole configuration and manipulate settings in the web GUI
and escalate privileges to highest access rights.

It is highly recommended by SEC Consult to perform a thorough security review
by security professionals for this platform. It is assumed that further critical
vulnerabilities exist within the firmware of this device.

Vulnerability overview/description:
-----------------------------------
1) Privilege escalation via linux group manipulation (CVE-2018-13110)
An attacker with standard / low access rights within the web GUI is able to
gain access to the CLI (if it has been previously disabled by the configuration)
and escalate his privileges.

Depending on the CLI features it is possible to extract the whole configuration
and manipulate settings or gain access to debug features of the device, e.g.
via "debug", "upgrade", "upload" etc. commands in the CLI.

Attackers can gain access to sensitive configuration data such as VoIP
credentials or other information and manipulate any settings of the device.

Proof of concept:
-----------------
1) Privilege escalation via linux group manipulation (CVE-2018-13110)
It is possible to manipulate the group name setting of "Storage users" and
overwrite the local linux groups called "remoteaccess" or "localaccess" in
(in /etc/group) which define access to Telnet or SSH on the ADB devices.

It may be possible to overwrite the "root" group as well but it may brick the
device and the default user is already within the "root" group. Hence this
attack has not been further tested.

The following steps describe the attack:
a) Add a new group called "localaccess" via the web GUI here:
http://$IP/ui/dboard/storage/storageusers?backto=storage

This will generate the following new group in /etc/group. The original
"localaccess" group will overwritten.

localaccess:Storage Group:5001:

b) Then delete this group via the web GUI again, the entry will be removed
from /etc/group completely.

c) Afterwards, create the following new group name entry via the web GUI and
add your user account (e.g. admin) which should have access to Telnet/SSH
now:

localaccess:x:20:root,admin,

d) Now the admin user has been added to the "localaccess" group and the "admin"
account is allowed to login via SSH or Telnet. Excerpt of new /etc/group:

localaccess:x:20:root,admin,:Storage Group:5001:

Further attacks on the CLI interface will not be described in detail within
this advisory. It is possible to add new user accounts with highest access rights
("newuser" command) or upload the whole configuration to a remote FTP server
("upload" command). The available feature-set of the CLI depends on the firmware
version.
The XML configuration is encrypted, but can be easily decrypted with access to the
firmware. Then it can be manipulated and uploaded to the device again ("upgrade"
command) which allows privilege escalation by changing permissions or roles
within this file.

Vulnerable / tested versions:
-----------------------------
The following specific devices & firmware have been tested which were the most
recent versions at the time of discovery:

The firmware versions depend on the ISP / customer of ADB and may vary!

ADB P.RG AV4202N - E_3.3.0, firmware version depending on ISP
ADB DV 2210 - E_5.3.0, firmware version depending on ISP
ADB VV 5522 - E_8.3.0, firmware version depending on ISP
ADB VV 2220 - E_9.0.6, firmware version depending on ISP
etc.

It has been confirmed by ADB that _all_ their ADB modems / gateways / routers
based on the Epicentro platform are affected by this vulnerability in all
firmware versions for all their customers (ISPs) at the time of identification
of the vulnerability _except_ those devices which have a custom UI developed
for the ISP.

Vendor contact timeline:
------------------------
2016-07-12: Contacting vendor ADB, sending encrypted advisory, asking about
affected devices
2016-07 - 2017-04: Further coordination, waiting for firmware release,
implementation & rollout phases for their customers
2018-07-04: Embargo lifted, public release of security advisory

Solution:
---------
The firmware versions depend on the ISP / customer of ADB and may vary!

Patch version:

ADB P.RG AV4202N >= E_3.3.2, firmware version depending on ISP
ADB DV2210 >= E_5.3.2, firmware version depending on ISP
ADB VV5522 >= E_8.3.2, firmware version depending on ISP
ADB VV2220 >= E_9.3.2, firmware version depending on ISP
etc.

Workaround:
-----------
Restrict access to the web interface and only allow trusted users.
Change any default/weak passwords to strong credentials.
Don't allow remote access to the web GUI via Internet.

Advisory URL:
-------------
https://www.sec-consult.com/en/vulnerability-lab/advisories/index.html

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

SEC Consult Vulnerability Lab

SEC Consult
Europe | Asia | North America

About SEC Consult Vulnerability Lab
The SEC Consult Vulnerability Lab is an integrated part of SEC Consult. It
ensures the continued knowledge gain of SEC Consult in the field of network
and application security to stay ahead of the attacker. The SEC Consult
Vulnerability Lab supports high-quality penetration testing and the evaluation
of new offensive and defensive technologies for our customers. Hence our
customers obtain the most current information about vulnerabilities and valid
recommendation about the risk profile of new technologies.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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EOF J. Greil / @2018