Month: October 2015

Categories
Fedora Sendmail

Vanity Top Level Domains – How To Block Them Using Sendmail

Oh the joy! More spam from those stupid ass new top level domains to scam people out of their money with worthless crap. By the time you are done reading this I am sure another TLD will sprout it’s spam wings and flood your mail server with it’s nonsense. Because the world is running out of TLDs so that someone can create hundreds of millions of bogus domains every day to harass us with. Yeah, that’s a good sustainable plan. No, nothing to do with making money.

How do we get rid of this stupid shit? It’s easy with Sendmail.

#cd /etc/mail

Edit the ‘access’ file and add the below list. I’ve sorted to make it easy to add more TLDs as they flood you with spam. This will be a weekly if not daily thing so get used to it. And yes, yes there is a .wang TLD.

# TLD Reject
accountant                REJECT
actor                    REJECT
airforce                REJECT
army                    REJECT
attorney                REJECT
auction                    REJECT
audio                    REJECT
band                    REJECT
blackfriday                REJECT
bid                    REJECT
christmas                REJECT
click                    REJECT
#club                    REJECT
consulting                REJECT
cricket                    REJECT
dance                    REJECT
date                    REJECT
degree                    REJECT
democrat                REJECT
dentist                    REJECT
diet                    REJECT
download                REJECT
engineer                REJECT
eu                    REJECT
faith                    REJECT
forsale                    REJECT
futbol                    REJECT
gift                    REJECT
gives                    REJECT
guitars                    REJECT
help                    REJECT
hiphop                    REJECT
hosting                    REJECT
lawyer                    REJECT
loan                    REJECT
link                    REJECT
market                    REJECT
men                    REJECT
mortgage                REJECT
navy                    REJECT
ninja                    REJECT
party                    REJECT
photo                    REJECT
pics                    REJECT
pro                    REJECT
property                REJECT
rehab                    REJECT
republican                REJECT
reviews                    REJECT
review                    REJECT
rip                    REJECT
rocks                    REJECT
science                    REJECT
sexy                    REJECT
show                    REJECT
social                    REJECT
software                REJECT
stream                    REJECT
tattoo                    REJECT
top                    REJECT
trade                    REJECT
us                    REJECT
wang                    REJECT
webcam                    REJECT
win                    REJECT
xyz                    REJECT

Save the file, make the db files and restart Sendmail.

Updated List as of 02/07/21

Categories
Fedora Sendmail

fail2ban – sendmail-auth – howto

This article is about fail2ban and preventing Sendmail brute force password attacks. Also known as fail2ban’s worthless sendmail-auth configuration.

fail2ban comes with a completely worthless sendmail-auth filter.  It looks for a failure notification from Sendmail that most likely will never happen anymore as previously the brute force attack would make one connection and issue multiple AUTH commands.  This is no longer the case. The brute force attack makes one connection, issues an AUTH command then disconnects and re-connects. This never triggers the Sendmail “possible SMTP attack: command=AUTH” string.

So, what we need to do is something, anything that actually has some sort of real world value, like it actually working? That’d be helpful, right?

#cd /etc/fail2ban/filter.d/
#cp sendmail-auth.conf sendmail-auth.local

Now edit the .local file and replace the worthless regex

failregex = ^%(__prefix_line)s\w{14}: (\S+ )?\[<HOST>\]( \(may be forged\))?: possible SMTP attack: command=AUTH, count=\d+$

With this

failregex = \[<HOST>\] .*to MTA
            \[<HOST>\] \(may be forged\)
            \[<HOST>\], reject.*\.\.\. Relaying denied

Save the file, then we want to reload fail2ban

# fail2ban-client reload
Categories
Fedora Other Sendmail

Sendmail – How To Disable IPv6 When Sending/Relaying

Well, we learned how to configure Sendmail to send to a specific IP address on a per domain basis. Google and it’s business service e-mail is now by default publishing IPv6 addresses for MX records, it’s almost impossible to do a per domain setup.  We do not want to disable IPv6 entirely on the server, but Sendmail keeps sending out via IPv6. How the hell do you make it stop!  It’s quite simple but just a refresher since this is a configuration that is out of sight and mind.  Remember that Sendmail is really two things. A Daemon (the part that listens for incoming mail) and a Client (the part that sends/relays e-mail). Naturally you have the DAEMON settings by default, but not the CLIENT settings.  So here we go.

I have only found one forum post regarding the proper solution to this problem.  It appears not to be properly documented and possibly this is changed behavior in a recent update. However, it does make sense.  Essentially you need to tell the IPv6 stack to use your IPv4 address.

Edit /etc/mail/sendmail.mc

Look for

DAEMON_OPTIONS(`Port=smtp,Addr=xxx.xxx.xxx.xxx, Name=MTA')dnl

Below the above line add this;

CLIENT_OPTIONS(`Family=inet6,Addr=::ffff:xxx.xxx.xxx.xxx')dnl

Save the file, make the db files and restart Sendmail.

Now, Sendmail will use IPv4 for it’s CLIENT operations.