ADB Group Manipulation Privilege Escalation

`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 ViehbAPck (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.  
  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
Interested to work with the experts of SEC Consult?  
Send us your application https://www.sec-consult.com/en/career/index.html  
  
Interested in improving your cyber security with the experts of SEC Consult?  
Contact our local offices https://www.sec-consult.com/en/contact/index.html  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
  
Mail: research at sec-consult dot com  
Web: https://www.sec-consult.com  
Blog: http://blog.sec-consult.com  
Twitter: https://twitter.com/sec_consult  
  
EOF J. Greil / @2018  
  
`