[VulnWatch] iDEFENSE Security Advisory 09.13.05: Linksys WRT54G Router Remote Administration Fixed Encryption Key Vulnerability

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

  • Next message: iDEFENSE Labs: "[VulnWatch] iDEFENSE Security Advisory 09.13.05: Linksys WRT54G 'restore.cgi' Configuration Modification Design Error Vulnerability"
    Date: Tue, 13 Sep 2005 17:15:35 -0400
    To: <bugtraq@securityfocus.com>, <vulnwatch@vulnwatch.org>, <full-disclosure@lists.grok.org.uk>

    Linksys WRT54G Router Remote Administration Fixed Encryption Key

    iDEFENSE Security Advisory 09.13.05
    September 13, 2005


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



    Remote exploitation of a design error in multiple versions of the
    firmware for Cisco Systems Inc.'s Linksys WRT54G wireless router may
    allow unauthenticated modification of the router configuration.

    The vulnerability specifically exists in the 'ezconfig.asp' handler of
    the httpd running on the internal interfaces, including by default
    the wireless interface. This handler is used by the 'ezSetup' to perform

    the initial setup of the router.

    struct mime_handler mime_handlers[] = {
    //{ "ezconfig.asp", "text/html", ezc_version, do_apply_ezconfig_post,
      do_ezconfig_asp, do_auth },
    /*Modified by Daniel(2004-09-06);*/
    { "ezconfig.asp", "text/html", ezc_version, do_apply_ezconfig_post,
      do_ezconfig_asp, NULL },

    The 'auth()' method for this page does not contain an authentication
    initialization function. As the authentication initializer (do_auth) was

    removed, no check is made when requesting the page. If the auth_fail
    flag was set for any reason, this call will fail. The code which sets
    the auth_fail flag is shown below. When the httpd starts, the value of
    auth_flag defaults to 0.

     if (handler->auth) {
         handler->auth(auth_userid, auth_passwd, auth_realm);
         auth_fail = 0;
         if (!auth_check(auth_realm, authorization))
             auth_fail = 1;

    The request returns an encrypted version of the configuration
    information, however the encryption on this data is very weak, it is a
    simple XOR based encryption, with a fixed 256 byte mask. In order to
    change the configuration, this key must be known. Once this key is known

    and the new configuration data is encrypted with it, and the new data
    can simply be posted to the httpd, the new configuration will take


    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).

    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
    internet access.

    Authentication credentials may be set if another user has attempted to
    view a page since the router was restarted. An attacker may be able to
    crash the httpd using another vulnerability, in which case it will
    restart within 2 minutes, with no authentication details initialized.
    This would then allow them to exploit the httpd with this vulnerability.


    iDEFENSE has confirmed the existence of this vulnerability in version
    3.01.03 of the firmware of the Linksys WRT54G, and has identified the
    same code is present in version 3.03.6.

    Version 2.04.4 of the WRT54G is confirmed to contain the affected code,
    however by default it initializes the authentication details, and so
    requires a password to set the configuration.


    In order to prevent exposure of this vulnerability from wireless
    disable wireless access to the web interface:

      * Connect to the web interface, typically at
      * Go to the Administration page
      * Select 'Disable' next to the 'Wireless Access Web'
      * Click the 'Save Settings' button.

    Please note that this will only prevent wireless access, and not access
    from one of the physical ports. Additionally, other vulnerabilities in
    the httpd may allow exploitation of the router, even with this setting

    In order to mitigate exposure of the router and 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.




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


    06/07/2005 Initial vendor notification
    06/07/2005 Initial vendor response
    09/13/2005 Coordinated public disclosure


    This vulnerability was discovered by Greg MacManus of iDEFENSE Labs.

    Get paid for vulnerability research

    Free tools, research and upcoming events


    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.

  • Next message: iDEFENSE Labs: "[VulnWatch] iDEFENSE Security Advisory 09.13.05: Linksys WRT54G 'restore.cgi' Configuration Modification Design Error Vulnerability"

    Relevant Pages