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Date: Thu, 21 Jul 2016 13:09:08 +0200
From: Gergely Eberhardt <gergely.eberhardt@...rch-lab.hu>
To: fulldisclosure@...lists.org
Subject: [FD] [SEARCH-LAB advisory] Ubee EVW3226 modem/router multiple
 vulnerabilities

Ubee EVW3226 modem/router multiple vulnerabilities
--------------------------------------------------

Platforms / Firmware confirmed affected:
- Ubee EVW3226, 1.0.20
- Product page: http://www.ubeeinteractive.com/products/cable/evw3226

Vulnerabilities
---------------
Insecure session management
The web interface does not use cookies at all. If admin login is
successful, the IP address of the admin user is stored and everybody can
access the management interface with the same IP.

Local file inclusion
Setup.cgi can read any file with .htm extension using directory
traversal in the gonext parameter. Although the file must have htm
extension, the local file inclusion can be used to map directories,
because the response is different depending on whether directory exists
or not.
POC:
http://<device_ip>/cgi-bin/setup.cgi?gonext=../www/main2
Backup file is not encrypted
Although the web interface requires a password for encrypting the backup
file, the encryption is not performed. In order to backup file password,
the plain password is stored in the backup file, which is a standard tgz
(gzipped tar) file with a simple header.

Backup file disclosure
When a user requests a backup file, the file is copied into www root in
order to make download possible. However, the backup file is not removed
from the www root after download. Since there is not any session check
required to download the backup file, an attacker is able to download it
without authentication from LAN until the next reboot.
Since the backup file is not encrypted and contains the plain admin
password, the router can be compromised from LAN.
POC:
http://<device_ip>/Configuration_file.cfg

Authentication bypass (backdoor)
The web interface bypasses authentication if the HTML request contains
the factoryBypass parameter. In this case a valid session is created and
the attacker can gain full control over the device.
POC:
http://<device_ip>/cgi-bin/setup.cgi?factoryBypass=1

Arbitrary code execution
The configuration file restore function receives a compressed tar file,
which is extracted to the /tmp folder. Tar files may contain symbolic
links, which can link out from the extraction folder. By creating a
configuration file with a symbolic link and a folder which uses this
link, the attacker can write out from the backup folder and can
overwrite any file in the writable file-system.
Since www is copied to the writable file system at boot time (under
/tmp), the attacker can insert a new cgi script that executes arbitrary
code with root privileges.

Default SSID and passphrase can be calculated
The default SSID and passphrase are derived only from the MAC address.
Since the MAC address of the device is broadcasted via WiFi, the default
password can be calculated easily.
Combined with code execution and factory bypass, even a botnet of Ubee
routers can be deployed easily.

Buffer overflow in configuration restore
During the configuration restore process, the backup file password is
read from the pass.txt file. If the password is large enough (larger
than 65536), a stack based buffer overflow is caused, because the file
content is loaded with fscanf(ā€œ%sā€) to a stack based local variable. The
stack based buffer overflow can be used to execute arbitrary code with
root privileges.

Buffer overflow in configuration file request
The web interface identifies the configuration file download request by
checking that the URL contains the Configuration_file.cfg string. If
this string is found, the whole URL is copied into a stack based buffer,
which can cause a buffer overflow. This stack based buffer overflow can
be used to execute arbitrary code with root privileges without
authentication.
POC:
http://192.168.0.1/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaConfiguration_file.cfg

Buffer overflow in next file name
The gonext variable in the POST requests specifies the HTML file, which
the cgi script should be loaded. If the gonext variable is large enough
(larger than 6512 bytes), a stack based buffer overflow is caused, which
can be used to execute arbitrary code with root privileges without
authentication.

Communication on the UPC Wi-Free can be sniffed within the device
The UPC Wi-Free communication is not separated correctly inside the
device, because the whole communication can be sniffed after gaining
root access to the device.

Timeline
--------
- 2015.06.24: Presenting the Ubee router problems to the CTO of UPC
Magyarorszag
- 2015.07.16: UPC contacted Ubee and required some more proof about some
specific problems
- 2015.07.16: Proofs, that the default passphrase calculation of the
Ubee router was broken, were sent to UPC
- 2015.07.20: UPC requested the POC code
- 2015.07.21: POC code was sent to UPC
- 2015.07.30: We sent some new issues affecting the Ubee router and
other findings in Technicolor TC7200 and Cisco EPC3925 devices to UPC
- Between 2015.07.31 and 08.12 there were several e-mail and phone
communications between technical persons from Liberty Global to clarify
the findings
- 2015.08.19: UPC sent out advisory emails to its end users to change
the default WiFi passphrase
- 2015.09.16: Ubee Interactive also asked some questions about the
vulnerabilities
- 2015.09.24: We sent detailed answers to Ubee Interactive
- 2016.01.27: UPC Magyarorszag send out a repeated warning to its end
users about the importance of the change of the default passphrases.
- 2016.02.16: Face to face meeting with Liberty Global security
personnel in Amsterdam headquarters
- 2016.02.18: A proposal was sent to Liberty Global suggesting a
wardriving experiment in Budapest, Hungary to measure the rate of end
users who are still using the default passphrases.

POC
---
POC script is available to demonstrate the following problems [3]:
- Authentication bypass
- Unauthenticated backup file access
- Backup file password disclosure
- Code execution

Video demonstration is also available [1], which presents the above
problems and how these can be combined to obtain full access to the modem.

Recommendations
---------------
Since only the ISP can update the firmware, we can recommend for users
to change the WiFi passphrase.

Credits
-------
This vulnerability was discovered and researched by Gergely Eberhardt
from SEARCH-LAB Ltd. (www.search-lab.hu)

References
----------
[1] http://www.search-lab.hu/advisories/secadv-20160720
[2] https://youtu.be/cBclw7uUuO4
[3] https://github.com/ebux/Cable-modems/tree/master/Ubee


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