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attachment with unknown extension issue with IE8

Discussion in 'Internet Explorer' started by rlastar, Mar 29, 2010.

  1. rlastar

    rlastar Flightless Bird

    My company save files with an unknown extension for security. When I receive
    an email (using gmail) with the file attached I save the file to a folder, it
    automatically changes the extension to .zip

    It's definitely and IE8 issue as with Firefox it saves the file with our
    unknown extension.

    I've checked Internet options but can't find what setting is causing this to
    happen.
    Any help is appreciated.

    Thanks
     
  2. Dan

    Dan Flightless Bird

    "rlastar" <rlastar@discussions.microsoft.com> wrote in message
    news:3796DBDB-79E0-471E-8574-E4576515EB08@microsoft.com...
    > My company save files with an unknown extension for security. When I
    > receive
    > an email (using gmail) with the file attached I save the file to a folder,
    > it
    > automatically changes the extension to .zip
    >
    > It's definitely and IE8 issue as with Firefox it saves the file with our
    > unknown extension.
    >
    > I've checked Internet options but can't find what setting is causing this
    > to
    > happen.
    > Any help is appreciated.
    >
    > Thanks


    IE uses "MIME Sniffing" if the content-type header and file extension can't
    be used to figure out the type of file.

    http://msdn.microsoft.com/en-us/library/ms775148(VS.85).aspx

    So, if these files are ZIP files as determined from the first 200 bytes of
    the file, IE will give them the .ZIP file extension (this may also occur
    with other file types that internally use ZIP compression, such as Office
    2007 compressed documents). This is a security feature in IE - it's designed
    to stop malicious attachments masquerading as something else.

    Security by obscurity is not a good practice. It's pretty trivial to
    determine the type of content of most files from the first few bytes, so
    using "unknown" file extension just ends up making things more difficult for
    humans but has little effect on software designed to figure out the file
    type as you've found out.

    --
    Dan
     

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