iDEFENSE Security Advisory 09.13.05: Linksys WRT54G 'upgrade.cgi' Firmware Upload 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 17:20:43 -0400
To: <bugtraq@securityfocus.com>, <vulnwatch@vulnwatch.org>, <full-disclosure@lists.grok.org.uk>

    Linksys WRT54G 'upgrade.cgi' Firmware Upload Design Error Vulnerability

    iDEFENSE Security Advisory 09.13.05
    www.idefense.com/application/poi/display?id=307&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 upgrade.cgi component of
    Cisco Systems Inc.'s Linksys WRT54G wireless router may allow
    unauthenticated modification of the router firmware.

    The vulnerability specifically exists in the "POST" method of the
    upgrade.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 upgrade.cgi handler allows a user to upload new
    firmware, which contains the operating system and applications, into the

    non-volatile memory of the router.

    If the user is authenticated, the router will then restart, and the new
    firmware will be loaded. If the user is not authenticated, they will
    receive an error page when they attempt to upload a new firmware without

    supplying authentication and the router will not reboot. The firmware
    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 completely compromise the affected
    router, by installation of an arbitrary firmware. As the source code and

    tools for compiling the firmware are available from the vendor, an
    attacker could simply rebuild the firmware and add the extra
    functionality. Exploitation of this vulnerability would require that an
    attacker 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). For the uploaded firmware to be enabled, the router
    must be restarted.

    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
    09/13/2005 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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