[NEWS] SurfControl Filter for SMTP Can Be Bypassed via Nested Zips

From: SecuriTeam (support_at_securiteam.com)
Date: 07/20/03

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    Date: 20 Jul 2003 20:47:46 +0200
    
    

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      SurfControl Filter for SMTP Can Be Bypassed via Nested Zips
    ------------------------------------------------------------------------

    SUMMARY

    SurfControl Filter for SMTP allows for SurfControl's filtering technology
    to be bolted on to your existing SMTP server. The rules engine contains a
    flaw whereby if an attachment is a .zip and it contains more than 15 zip
    files, the 16th zip file will not be scanned by the filter. This probably
    works with other archive/file types and possibly on other SurfControl
    products.

    DETAILS

    Vulnerable systems:
     * SurfControl Filter for SMTP version 4.6

    In order to bypass the filter build a .zip as below:

    attach.zip - dummy_folder - a.zip - junk.txt
                              - b.zip - junk.txt
                              - c.zip - junk.txt
                              - d.zip - junk.txt
                              - e.zip - junk.txt
                              - f.zip - junk.txt
                              - g.zip - junk.txt
                              - h.zip - junk.txt
                              - i.zip - junk.txt
                              - j.zip - junk.txt
                              - k.zip - junk.txt
                              - m.zip - junk.txt
                              - n.zip - junk.txt
                              - o.zip - junk.txt
                              - p.zip - junk.txt
               - z.zip - sneaky.exe << Passes thru!

    (The filter sorts the files in attach.zip alphabetically so we name our
    files a, b, c, etc to be sure that z.zip is last)

    ADDITIONAL INFORMATION

    The information has been provided by <mailto:Lee@networkpenetration.com>
    Lee Bowyer.

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