OSEC

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From: Peter Gründl (pgrundlkpmg.dk)
Date: Mon Mar 18 2002 - 03:41:51 CST

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            -=>BitVise WinSSH Denial of Service<=-
                          courtesy of KPMG Denmark

    BUG-ID: 2002005 Released: 18th Mar 2002
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    Problem:
    ========
    Using "ill-intended connection attempts", a malicious user could
    bring the server to a state where it would no longer accept incoming
    SSH connections.

    Vulnerable:
    ===========
    - BitVise WinSSH prior to build 2002-03-16 on Windows 2000 Server

    Details:
    ========
    Due to differences in the SSHd and the underlying socket layer, it
    was possible to abruptly end sessions and not have those freed
    properly by the sshd. Each incomplete connection would use up a few
    memory handles and allocate nonpaged kernel memory.

    Windows can only handle a certain amount of kernel memory being
    allocated, after that point most applications begin acting peculiar.

    During testing we repeatedly caused the server to no longer accept
    connections to port 22 (connection refused). This took about
    1840x254 connections, but since it's not time or bandwidth related,
    this attack could be carried out from a normal modem dialup,
    and still be succesful.

    The vendor has limited the amount of simultaneous unathenticated
    sessions and put a timeout of 60 seconds on each connection.

    Vendor URL:
    ===========
    You can visit the vendors webpage here: http://www.bitvise.com

    Vendor response:
    ================
    The vendor was contacted on the 25th of February, 2002. On the
    16th of March the vendor released the new build, that corrected
    the issue. On the 18th of January, 2002, it was confirmed that the
    patch corrected the issue mentioned in this advisory.

    Corrective action:
    ==================
    Upgrade to the latest build, which can be downloaded here:
    http://www.bitvise.com/existing-users.html

       Author: Peter Gründl (pgrundlkpmg.dk)

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    through our security advisories. These advisories are a service to
    the professional security community. In no event shall KPMG be lia-
    ble for any consequences whatsoever arising out of or in connection
    with the use or spread of this information.
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