README.SECURITY

SECURITY
--------

Here are some tips for improving the security of your MIMEDefang installation.

1) Do NOT run mimedefang or mimedefang-multiplexor as root.  (In fact,
modern versions of MIMEDefang explicitly prohibit this.)  If you start
them as root, use the "-U" flag to get them to drop their privileges.
I recommend creating a dedicated "defang" user just for MIMEDefang.
See README.NONROOT

2) Use the multiplexor, and use the "-M" option to limit the memory space
of workers.  A limit of 50000 (50MB) should be OK on most CPU architectures.
If you don't limit the worker address space, specially-crafted MIME
messages can make workers consume lots of memory and grind your box to
a thrashing halt.

3) Be wary of virus scanners which look into compressed archives.
Compressing large blocks of zeros can result in small archives which
lead to denial-of-service when uncompressed.  Depending on your scanner,
the "-M" option may mitigate this.

4) Do not use "action_notify_sender" unless you are absolutely, 100%
sure that the sender address has not been spoofed.  Oh, by the way, it
is impossible to be sure the sender address has not been spoofed.

5) You may use action_bounce, but use it with care.  You may wish to
test the sender address first.  (For example, don't bounce a message
if the relay it was received from is not an MX host for the purported
sender's domain.)