iDEFENSE Security Advisory 02.22.05: phpBB Group phpBB Arbitrary File Disclosure Vulnerability

From: iDEFENSE Labs (labs-no-reply_at_idefense.com)
Date: 02/22/05

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    Date: Tue, 22 Feb 2005 11:10:39 -0500
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    phpBB Group phpBB Arbitrary File Disclosure Vulnerability

    iDEFENSE Security Advisory 02.22.05
    www.idefense.com/application/poi/display?id=204&type=vulnerabilities
    February 22, 2005

    I. BACKGROUND

    phpBB is an open source bulletin board package written in the PHP web
    scripting language. More information about phpBB is available from:

        http://www.phpbb.com/

    II. DESCRIPTION

    Remote exploitation of an input validation vulnerability in the phpBB
    Group's phpBB2 bulletin board system allows attackers to read the
    contents of arbitrary system files under the privileges of the web
    server.

    phpBB is an open-source web-based bulletin board system written in PHP.
    The problem specifically exists due to an input validation error that
    allows a remote attacker to control the arguments in a call to copy().

    When a user requests to upload an avatar, the variable
    '$user_avatar_upload' defaults to uploading from a remote URL and the
    variable '$avatar_mode' defaults to uploading from the local computer.
    The variable '$user_avatar_upload' contains either the remote URL or the
    temporary server name depending on whether the source of the avatar to
    upload is local or remote. In the event that both a local and remote
    upload are requested simultaneously, the temporary upload location is
    substituted with the remote server name. This will later be copied to
    the new location. By submitting a local path rather then a URL, an
    attacker is able to execute an arbitrary copy() command.

    An attacker can exploit this input validation condition by selecting an
    avatar from the local machine that meets the board guidelines and can
    then fill the "Upload Avatar from a URL:" field with the path to an
    arbitrary file (ex: /etc/passwd). When the avatar is submitted, the
    destination image of the submitted avatar will contain the contents of
    the requested file.

    III. ANALYSIS

    Exploitation of this vulnerability allows remote attackers to view
    arbitrary system files under the privileges of the underlying web
    server. An attacker must have, or be able to create an account on the
    target system. Non-default settings must also be enabled for
    exploitation to be possible. Upon successful exploitation an attacker
    may be able to further compromise the system by gleaning system
    information that would otherwise be inaccessible to the attacker.

    IV. DETECTION

    iDEFENSE has confirmed the existence of this vulnerability in phpBB2
    version 2.0.11. It is suspected that earlier versions are affected as
    well. "Enable remote avatars" and "Enable avatar uploading" must be
    enabled for the target to be vulnerable.

    V. WORKAROUND

    Disable remote avatars and remove avatar uploading. This can be done
    through th phpBB administrative interface under "General Admin ->
    Configuration -> Avatar Settings". Alternatively, enable the
    'open_basedir' PHP security directive to lock file I/O operations to a
    specific directory.

    VI. VENDOR RESPONSE

    This vulnerability is addressed in phpBB version 2.0.12 available for
    download at:

       http://www.phpbb.com/downloads.php

    VII. CVE INFORMATION

    The Common Vulnerabilities and Exposures (CVE) project has assigned the
    names CAN-2005-0259 to these issues. This is a candidate for inclusion
    in the CVE list (http://cve.mitre.org), which standardizes names for
    security problems.

    VIII. DISCLOSURE TIMELINE

    02/09/2005 Initial vendor notification
    02/11/2005 Initial vendor response
    02/22/2005 Public disclosure

    IX. CREDIT

    AnthraX101 (AnthraX101[at]gmail.com) is credited with this discovery.

    Get paid for vulnerability research
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    X. LEGAL NOTICES

    Copyright (c) 2005 iDEFENSE, 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 iDEFENSE. If you wish to reprint the whole or any
    part of this alert in any other medium other than electronically, please
    email customerservice@idefense.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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