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Topic: exe and bat files slipping through

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Good afternoon,

Earlier today a couple users received this email from our exchange server (iredmail sits between the internet and exchange acting only as a spam filter):

The message or an attachment did not reach the intended recipient(s).!
  Subject: Order Details
     From: odiousmwt@dramaawork.us
       To: asandoval@coatsandbennett.com
     Date: Mon, 07 Jul 2014 17:47:53 GMT
   Reason: attachment type policy violation (report_id_875893475983475934759384.exe)
   Action: quarantine

After running some tests from www.emailsecuritycheck.net I've discovered that bat files may be passed through also, although the exe files from the test were blocked. How can I tighten amavisd up so that any kind of exe or bat file will be blocked? Below are my current amavisd config for banned file types:

-------
$banned_filename_re = new_RE(

### BLOCKED ANYWHERE
# qr'^UNDECIPHERABLE$',  # is or contains any undecipherable components
  qr'^\.(exe-ms|dll|bat|exe)$',                   # banned file(1) types, rudimentary
# qr'^\.(exe|lha|cab|dll)$',              # banned file(1) types

### BLOCK THE FOLLOWING, EXCEPT WITHIN UNIX ARCHIVES:
# [ qr'^\.(gz|bz2)$'             => 0 ],  # allow any in gzip or bzip2
  [ qr'^\.(rpm|cpio|tar)$'       => 0 ],  # allow any in Unix-type archives

  qr'.\.(pif|scr|bat)$'i,                     # banned extensions - rudimentary
# qr'^\.zip$',                            # block zip type

### BLOCK THE FOLLOWING, EXCEPT WITHIN ARCHIVES:
# [ qr'^\.(zip|rar|arc|arj|zoo)$'=> 0 ],  # allow any within these archives

  qr'^application/x-msdownload$'i,        # block these MIME types
  qr'^application/x-msdos-program$'i,
  qr'^application/hta$'i,

# qr'^message/partial$'i,         # rfc2046 MIME type
# qr'^message/external-body$'i,   # rfc2046 MIME type

# qr'^(application/x-msmetafile|image/x-wmf)$'i,  # Windows Metafile MIME type
# qr'^\.wmf$',                            # Windows Metafile file(1) type

  # block certain double extensions in filenames
  qr'^(?!cid:).*\.[^./]*[A-Za-z][^./]*\.\s*(exe|vbs|pif|scr|bat|cmd|com|cpl|dll)[.\s]*$'i,

# qr'\{[0-9a-f]{8}(-[0-9a-f]{4}){3}-[0-9a-f]{12}\}?'i, # Class ID CLSID, strict
# qr'\{[0-9a-z]{4,}(-[0-9a-z]{4,}){0,7}\}?'i, # Class ID extension CLSID, loose

  qr'.\.(exe|vbs|pif|scr|cpl|bat)$'i,             # banned extension - basic
# qr'.\.(exe|vbs|pif|scr|cpl|bat|cmd|com)$'i, # banned extension - basic+cmd
# qr'.\.(ade|adp|app|bas|bat|chm|cmd|com|cpl|crt|emf|exe|fxp|grp|hlp|hta|
#        inf|ini|ins|isp|js|jse|lib|lnk|mda|mdb|mde|mdt|mdw|mdz|msc|msi|
#        msp|mst|ocx|ops|pcd|pif|prg|reg|scr|sct|shb|shs|sys|vb|vbe|vbs|vxd|
#        wmf|wsc|wsf|wsh)$'ix,                # banned extensions - long
# qr'.\.(asd|asf|asx|url|vcs|wmd|wmz)$'i,     # consider also
# qr'.\.(ani|cur|ico)$'i,                 # banned cursors and icons filename
# qr'^\.ani$',                            # banned animated cursor file(1) type
# qr'.\.(mim|b64|bhx|hqx|xxe|uu|uue)$'i,  # banned extension - WinZip vulnerab.
);
-------

Thank you,
Luke

2

Re: exe and bat files slipping through

You already found where to set banned file extensions, so please just update it to ban '.bat' (or whatever extensions you want) in "$banned_filename_re = new_RE()" block. It also provides sample setting for your use:

$banned_filename_re = new_RE(
    ...
    qr'.\.(exe|vbs|pif|scr|cpl|bat)$'i,             # banned extension - basic
    # qr'.\.(exe|vbs|pif|scr|cpl|bat|cmd|com)$'i, # banned extension - basic+cmd
    ...
);

3

Re: exe and bat files slipping through

Maybe I'm missing something but I already have 'bat' and 'exe' listed everywhere I can find but they are still getting through...I'm assuming I don't need the dot before bat or exe...MIME type maybe?

Thanks!
Luke