Privilege escalation via linux group manipulation in all ADB Broadband Gateways

Project Description

All ADB broadband gateways / routers based on the Epicentro platform used by many telecommunication providers (ISPs) world-wide are affected by a privilege escalation vulnerability where attackers can gain access to the command line interface (CLI) if previously disabled by the ISP, escalate their privileges and perform further attacks.

Also see our other two advisories regarding critical ADB vulnerabilities as they have been split up for better readability:
Local root jailbreak via network file sharing flaw in all ADB Broadband Gateways / Routers
Authorization Bypass in all ADB Broadband Gateways / Routers


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 /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

 

 

EOF J. Greil / @2018

 

Project Details

  • TitlePrivilege escalation via linux group manipulation
  • ProductAll ADB Broadband Gateways / Routers (based on Epicentro platform)
  • Vulnerable versionHardware: ADB P.RG AV4202N, DV2210, VV2220, VV5522, etc.
  • Fixed versionsee "Solution" section below
  • CVE numberCVE-2018-13110
  • ImpactCritical
  • Homepagehttp://www.adbglobal.com
  • Found2016-07-11
  • ByStefan Viehböck (Office Vienna) | Johannes Greil (Office Vienna) | SEC Consult Vulnerability Lab

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