[Full-disclosure] Webmin miniserv.pl format string vulnerability

advisory_at_dyadsecurity.com
Date: 11/29/05

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    Date: Tue, 29 Nov 2005 02:07:10 -0800
To: full-disclosure@lists.grok.org.uk

    SUMMARY. The webmin `miniserv.pl' web server component is vulnerable to
    a new class of exploitable (remote code) perl format string
    vulnerabilities. During the login process it is possible to trigger this
    vulnerability via a crafted username parameter containing format string
    data. In the observed configuration the process was running as the user
    root, so so if remote code execution is successful, it would lead to a
    full remote root compromise in a standard configuration. A valid login
    is not required to trigger this vulnerability, only access to the
    miniserv.pl port (default 10000).

    Date Found: September 23, 2005.
    Public Release: November 29, 2005.
    Application: webmin miniserv.pl, all known versions
    Credit: Jack Louis of Dyad Security

    BACKGROUND. miniserv.pl is a part of the webmin system administration
    front end, written in perl by Jamie Cameron. more details are available
    at http://www.webmin.com.

    DESCRIPTION. The username parameter of the login form is logged via the
    perl `syslog' facility in an unsafe manner during a unknown user login
    attempt. the perl syslog facility passes the username on to the variable
    argument function sprintf that will treat any format specifiers and
    process them accordingly.

    DETAILS. The vectors for a simple DoS of the web server are to use the
    %n and %0(large number)d inside of the username parameter, with the
    former causing a write protection fault within perl leading to script
    abortion, and the latter causing a large amount of memory to be
    allocated inside of the perl process.

    A generic remote code execution exploit method has been developed by a
    third party that is reachable though this hole itself.

    The following is the section of code in question. (from miniserv.pl)

    if ($use_syslog && !$validated) {
            syslog("crit",
                   ($nonexist ? "Non-existent" :
                    $expired ? "Expired" : "Invalid").
                   " login as $authuser from $acpthost");
            }

    As can be clearly seen with this section of code, the user supplied data
    is clearly within the format specification of the syslog call.

    Additional information and sample work around patches can be found at
    http://www.dyadsecurity.com/webmin-0001.html

    LEGAL NOTICES.
    Copyright (C) 2005 Dyad Security, Inc.

    Permission is granted for the redistribution of this alert
    electronically. It may not be edited in any way without the express
    written consent of Dyad Security, Inc. If you wish to reprint the whole
    or any part of this alert in any other medium other than electronically,
    please email advisoryreprint@dyadsecurity.com for permission.

    DISCLAIMER. The information in the advisory is believed to be accurate
    at the time of publishing based on currently available information. Use
    of the information constitutes acceptance for use in an AS IS condition.
    There are no warranties with regard to this information. Neither the
    author nor the publisher accepts any liability for any direct, indirect,
    or consequential loss or damage arising from use of, or reliance on,
    this information.
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