iDEFENSE Security Advisory 09.13.05: Linksys WRT54G 'restore.cgi' Configuration Modification Design Error Vulnerability

From: iDEFENSE Labs (labs-no-reply_at_idefense.com)
Date: 09/13/05

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    Date: Tue, 13 Sep 2005 17:16:46 -0400
To: <bugtraq@securityfocus.com>, <vulnwatch@vulnwatch.org>, <full-disclosure@lists.grok.org.uk>

    Linksys WRT54G 'restore.cgi' Configuration Modification Design Error
    Vulnerability

    iDEFENSE Security Advisory 09.13.05
    www.idefense.com/application/poi/display?id=306&type=vulnerabilities
    September 13, 2005

    I. BACKGROUND

    The Linksys WRT54G is a combination wireless access point, switch and
    router. More information is available at the following URL:

      http://www.linksys.com/products/product.asp?prid=508

    II. DESCRIPTION

    Remote exploitation of a design error in the 'restore.cgi' component of
    Cisco Systems Inc.'s Linksys WRT54G wireless router may allow
    unauthenticated modification of the router configuration.

    The vulnerability specifically exists in the 'POST' method of
    restore.cgi handler. The httpd running on the internal interfaces,
    including by default the wireless interface, does not check if
    authentication has failed until after data supplied by an external user
    has been processed. The restore.cgi handler allows a user to upload a
    new configuration into the non-volatile memory of the router. If the
    user is authenticated, the router will then restart, and the new
    configuration will be loaded.

    If the user is not authenticated, they will receive an error page when
    they attempt to upload a new configuration without supplying
    authentication and the router will not reboot. The settings the user
    set will be saved, but will not take effect until the next time the
    router restarts.

    III. ANALYSIS

    Successful exploitation of this vulnerability would allow an
    unauthenticated user the ability to modify the configuration of the
    affected router, including the password. This could allow firewall
    rules to be changed, installation of a new firmware with other
    features, or denial of service. Exploitation of this vulnerability
    would require that an attacker can connect to the web management port
    of the router. The httpd is running by default but is only accessible
    via the LAN ports or the WLAN (wireless LAN). A mitigating factor is
    that if the firmware settings are saved by a process on the router
    before the server is reset, the saved settings will overwrite the
    settings uploaded by the attacker.

    An attacker who can associate with a network running a vulnerable httpd
    could send an exploit from a wireless device to reset the password on
    the device and enable the remote management port, allowing continued
    access from the Internet.

    IV. DETECTION

    iDEFENSE has confirmed the existence of this vulnerability in version
    3.01.03 of the firmware of the Linksys WRT54G wireless router, and has
    identified the same code is present in versions 3.03.6 and 4.00.7. All
    versions prior to 4.20.7 may be affected.

    V. WORKAROUND

    To mitigate exposure of the internal network to outside attackers,
    ensure encryption is enabled on the wireless interface. The exact
    settings to use are dependent on your wireless deployment policies.

    VI. VENDOR RESPONSE

    This vulnerability is addressed in firmware version 4.20.7 available for
    download at:

    http://www.linksys.com/servlet/Satellite?childpagename=US%2FLayout
     
    &packedargs=c%3DL_Download_C2%26cid%3D1115417109974%26sku%3D112491680264
    5
     &pagename=Linksys%2FCommon%2FVisitorWrapper

    VII. CVE INFORMATION

    A Mitre Corp. Common Vulnerabilities and Exposures (CVE) number has not
    been assigned yet.

    VIII. DISCLOSURE TIMELINE

    07/05/2005 Initial vendor notification
    07/25/2005 Initial vendor response
    09/12/2005 Coordinated public disclosure

    IX. CREDIT

    This vulnerability was discovered by Greg MacManus of iDEFENSE Labs.

    Get paid for vulnerability research
    http://www.idefense.com/poi/teams/vcp.jsp

    Free tools, research and upcoming events
    http://labs.idefense.com

    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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