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From: Franklin DeMatto (franklinqDefense.com)
Date: Tue May 15 2001 - 13:52:33 CDT

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    DCForum Password File Manipulation Vulnerability
    qDefense Advisory Number QDAV-5-2000-2

    Product: DCForum

    Vendor: D.C. Script

    Version Tested: DCForum 2000 1.0 (Version 6.0 is believed to be vulnerable as well)

    Severity: Remote; Any attacker may gain DCForum admin privileges, which result in read/write/execute privileges

    Cause: Failure to validate input

    The current version of this document is available at http://qDefense.com/Advisories/QDAV-5-2000-2.html.

    DCForum is a popular CGI to create message boards on web sites.

    It is vulnerable to an attack which will grant a remote attacker the status of DCForum administrator, which can then be used to execute arbitrary commands on the server.

    The DCForum password file (normally the file auth_user_file.txt, located in the /cgi-bin/dcforum/User_info directory), stores the user info in a text file database, using the pipe symbol ( | ) as a delimiter by default. Here is a sample file:

    1ejq5eWn718pA|bill|admin|William|Smith|webmasterletstalksports.com|on
    mgHX9HISAezfQ|joe|normal|Joe|Smith|joemailboxesrus.com|on
    67NuyNzElLQs.|iceman|normal|Alfred|Lehoya|js124abracadabra.com|on
    79NAtkW0UxFWE|hank|normal|Harold|Jenkins|hjenkinsaricdorsresearch.org|on

    By registering with a last name containing url-encoded newlines and pipes, an attacker can imbed a second line into his last name, which will be recorded as an entirely new line in the password file, containing whatever information the attacker wants. For instance, an attacker may register as follows:

    Username = dummyuser
    Password = *****
    Password again = *****
    Firstname = John
    Lastname = Doe\nzzw1I3xWVi.zE|evilhacker|admin|Evil|Hacker
    Email = evilhackerstogo.com
    When url encoded and submitted properly, this will add two lines to the auth_user_file.txt. The example auth_user_file.txt will now look like this:

    1ejq5eWn718pA|bill|admin|William|Smith|webmasterletstalksports.com|on
    mgHX9HISAezfQ|joe|normal|Joe|Smith|joemailboxesrus.com|on
    67NuyNzElLQs.|iceman|normal|Alfred|Lehoya|js124abracadabra.com|on
    79NAtkW0UxFWE|hank|normal|Harold|Jenkins|hjenkinsaricdorsresearch.org|on
    fgRldEzNsQL1p|dummyuser|normal|John|Doe
    zzw1I3xWVi.zE|evilhacker|admin|Evil|Hacker|evilhackerstogo.com|on

    As you can see, an entry, evilhacker, has been added with full admin status. This account can be used provided that the password hash given, zzw1I3xWVi.zE, was constructed from a known password (in this case it was "gotya"). This technique will work even if DCForum is set to e-mail passwords, and, with a minor modification, will work even if accounts are not enabled automatically. Once admin status has been acquired, an attacker can execute arbitrary commands. The easiest way for an attacker to do this is to set the sendmail program to the command the attacker wants to execute, set DCForum to e-mail the admin upon new registration, and then to register a new user.

    Proof of concept:

    A fully working proof-of-concept script, dcgetadmin.pl, is available at the qDefense web site ( http://qDefense.com/downloads/dcgetadmin_pl.txt).

    Franklin DeMatto
    franklinqDefense.com
    qDefense - DEFENDING THE ELECTRONIC FRONTIER