Vulnerability in Linksys Router access

Discussion in 'General Discussion' started by Mr_X, Jul 28, 2005.

  1. Mr_X

    Mr_X Network Guru Member

    From :

    Many months ago, I reported a vulnerability to Linksys/Cisco regarding
    the WRT54G. The vulnerability is simple: SSL is used to secure
    communications with the router.

    That is a good thing. However, SSL is not secure when you just
    implement part of it. SSL was implemented in a miserably insecure
    manner. All routers used the same certificate and private key. The
    certificate and private key were part of the software load.

    Thus, anyone who works at it a very small amount and who records the SSL
    entire session can decrypt it.

    The software writers are caught between a rock and a hard place in terms
    of how to implement certificates. Self signed certificates are at risk
    for MITM (Man In The Middle) attacks. Anyone can dynamically self sign a
    certificate and present it. Certificates that are signed by a well
    known certifying agency or even using a common signing certificate
    programmed into a browser (where the signing certificate's private key
    is properly protected) help prevent MITM attacks due to details of SSL.

    But you need a different certificate/key pair for every presenter, and
    you need to secure the key.

    Installing a different certificate signed by a well known certifying
    agency into each separate software load would require that EVERY
    different router have a unique software load. It might well also
    increase the cost of the router significantly. These routers are
    $49.99, quantity 1, through The cost of a certificate would
    be a significant fraction of that amount.

    So you have three possibilities:

    1. A common certificate.
    2. Individual software loads.
    3. dynamically built, randomly generated self-signed certificates.

    I was assured shortly after I reported this, that the newer versions of
    the router software would be changed to build a random private key and
    use a self-signed certificate. I have not installed the latest version
    of my software in my router, so I can't attest to this. They didn't
    answer my last few e-mails.

    Many people configure these routers by simply accessing a wired directly
    connected router using a browser. Arguably, it does not matter whether
    that initial encryption is secure or not, since the wire is arguably
    secure. If a random, self-signed certificate is used, then the
    certificate fingerprint can be recorded.

    If you then tell your browser to keep accepting that certificate, you
    should be notified if, later, a MITM attack is undertaken - the MITM
    attacker should present some other certificate.

    You should assume that if you are using ssl to access a router where the
    path to the router is in an adverse environment, and you are using a
    version of the software where a shared private key and shared
    certificate are used, that your communication might be intercepted and

    If you are using a randomly generated key, you should record the key
    fingerprint, either using a browser facility or manually, and then, when
    you contact the router, you should verify that you are using the same

    If these routers are used in an adverse environment, administrators
    might consider installing a different private key and certificate in
    each software load. In that case, the private key and associated
    certificate could be used with a single signing key and the browser used
    to access those routers could accept that signing key.
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