Attachment filtering must remove undesirable attachments by file type.

From Exchange 2010 Edge Transport Server STIG

Part of Exch-2-302

SV-44057r2_rule Attachment filtering must remove undesirable attachments by file type.

Vulnerability discussion

By performing filtering at the perimeter, up to 90 percent of spam, malware, and other undesirable messages are eliminated from the message stream rather than admitting them into the mail server environment. Attachments are being used more frequently for different forms of attacks. By filtering undesirable attachments a large percent of malicious code can be prevented from entering the system. Attachments must be controlled at the entry point into the email environment to prevent successful attachment-based attacks. The following is a basic list of known attachments that should be filtered from Internet mail attachments.*.ade *.crt *.jse *.msi *.scr *.wsh *.dir *.adp *.csh *.ksh *.msp *.sct *.htm *.dcr *.app *.exe *.lnk *.mst *.shb *.html *.plg *.asx *.fxp *.mda *.ops *.shs *.htc *.spl *.bas *.hlp *.mdb *.pcd *.url *.mht *.swf*.bat *.hta *.mde *.pif *.vb *.mhtml *.chm *.inf *.mdt *.prf *.vbe *.shtm *.cmd *.ins *.mdw *.prg *.vbs *.shtml *.com *.isp *.mdz *.reg *.wsc *.stm *.cpl *.js *.msc *.scf *.wsf

Check content

Obtain the Email Domain Security Plan (EDSP) and locate the list of undesirable attachment types that should be stripped. Open the Exchange Management Shell and enter the following command: Get-AttachmentFilterEntry If the values returned are different from the EDSP documented attachment types, this is a finding.

Fix text

Open the Exchange Management Shell and enter the following command: Add-AttachmentFilterEntry -Name <'*.FileExtension'> -Type FileName

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