Linux

Blocking .wwf attachments

Some idiotic german 'invented' a way to 'save trees'. By converting your attachments to .wwf format - a special .pdf format that blocks printing. While this may be a great feature to block printing of contracts etcetera if you're running a malicious company, most people simply don't want this.

So the big question is: How do I block .wwf files?

Postfix

In /etc/postfix/main.cf uncomment or add the following line
header_checks = pcre:/etc/postfix/header_checks

Then edit /etc/postfix/header_checks and add the following line:
/Content-Disposition: .*\.wwf"/ REJECT Please don't send .wwf files.

Exchange

Attachment blocking in exchange is usually performed by a virusscanner/spamfilter. You could use for example Trend Micro or GFI to block .wwf files.

Sendmail

Depending on your setup, you could use amavisd-new, mailscanner or procmail to block out .wwf files.

qmail

To block attachments with qmail, you'll need Simscan. Simscan is a simple program that enables the qmail smtpd service to reject viruses, spam, and block attachments during the SMTP conversation so the processing load on the email system is kept to a minimum. The project is open source and uses other open source components. Small, very efficient and written in C.

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4 comments on “Blocking .wwf attachments”

  1. You can also convert them using onboard tools like Ghostscript and Poppler utils. Can't you program your mailing server in such a way that it converts it to a printble PDF and return it? ;-)

  2. Hi Hans, thanks for your reply! Converting them using ghostscript and poppler is an interesting idea. I'm not sure if that can be done. I read that the files are actually pdfs with printing disabled and a password. That would probably mean you can't use gs/poppler either.

    But then again, even if you can open them, accepting them would mean that the sender thinks you like their actions. If you simply block it, the originator will be forced to send a normal file.

    If gs/poppler can use .wwf files, you can indeed create a filter that replaces the file. With Sendmail you can use milters to perform such an action. On Postfix, my personal favorite, you can define a content_filter just like amavisd-new.

    By the way, the Postfix content filters and destinations are a great way to perform all sorts of tasks. For instance, I have a special email-address that automatically prints all PDFs (invoices) send to it. Think I'll write a post about that soon.

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