Dealing with SMTP invalid command attack

Posted by mark on Server Fault See other posts from Server Fault or by mark
Published on 2012-09-03T16:47:06Z Indexed on 2012/09/03 21:39 UTC
Read the original article Hit count: 223

Filed under:

linux

|

security

|

smtp

|

sendmail

One of our semi-busy mail servers (sendmail) has had a lot of inbound connections over the past few days from hosts that are issuing garbage commands.

In the past two days:

incoming smtp connections with invalid commands from 39,000 unique IPs
the IPs come from various ranges all over the world, not just a few networks that I can block
the mail server serves users throughout north america, so I can't just block connections from unknown IPs
sample bad commands: http://pastebin.com/4QUsaTXT

I am not sure what someone is trying to accomplish with this attack, besides annoy me.

any ideas what this is about, or how to effectively deal with it?

© Server Fault or respective owner

Related posts about linux

apt-get install and update fail

as seen on Ask Ubuntu - Search for 'Ask Ubuntu'
I've got a problem with apt-get update and apt-get install ... commands . every time update or installing fails and errors are : Get:1 http://dl.google.com stable Release.gpg [198B] Ign http://dl.google.com/linux/chrome/deb/ stable/main Translation-en_US Get:2 http://dl… >>> More
kernel module compiling error

as seen on Ask Ubuntu - Search for 'Ask Ubuntu'
sh@ubuntu:/home/ccpp/helloworld$ make gcc-4.6 -O2 -DMODULE -D_KERNEL_ -W -Wall -Wstrict-prototypes -Wmissing-prototypes -isystem /lib/modules/`uname -r`/build/include -c -o hello-1.o hello-1.c hello-1.c:4:0: warning: "MODULE" redefined [enabled by default] <command-line>:0:0: note: this is… >>> More
Build-Essentials installation failing

as seen on Ask Ubuntu - Search for 'Ask Ubuntu'
I am having trouble accessing the several critical header files that show to be a part of the build process. The "Ubuntu Software Center" shows "Build Essentials" as installed: Next I did the following two commands, which did not improve the problem: ~$ sudo apt-get install build-essential [sudo]… >>> More
Updating Debian kernel

as seen on Super User - Search for 'Super User'
I'm trying to update my Debian machine to 2.6.32-46 (which is the new stable). However, after doing apt-get update my apt-cache search linux-image shows me: linux-headers-2.6.32-5-486 - Header files for Linux 2.6.32-5-486 linux-headers-2.6.32-5-686-bigmem - Header files for Linux 2.6.32-5-686-bigmem linux-headers-2… >>> More
Serial connection over a single USB cable (Windows to linux, or linux to linux)

as seen on Server Fault - Search for 'Server Fault'
I'm helping out with a project for an embedded device that only has USB and no serial. This device is running Linux. These days, when we need to connect to a serial port on a device we typically use a USB to serial adapter (on something like a phone system or a load balancing device, etc). I would… >>> More

Related posts about security

sudo apt-get update errors

as seen on Ask Ubuntu - Search for 'Ask Ubuntu'
Here is what I get on my terminal when running sudo apt-get update errors. I dont know if the issue is from my sources.list or my proxy setup(have not made any changes to proxies). Thank you for any help in advanced. Ign http://security.ubuntu.com oneiric-security Release.gpg Ign http://security… >>> More
The Security-Developer Gap: Why IT Security Can't Fix Your Security Problems Alone

as seen on Devx - Search for 'Devx'
Two well-known white hats explain how hackers take advantage of security holes left by enterprise application developers. >>> More
The Security-Developer Gap: Why IT Security Can't Fix Your Security Problems Alone

as seen on Internet.com - Search for 'Internet.com'
Two well-known white hats explain how hackers take advantage of security holes left by enterprise application developers. >>> More
StackOverFlowError while creating Mac object on AS400/Java

as seen on Stack Overflow - Search for 'Stack Overflow'
Hello all, I am a newbie to AS400-Java programming. I am trying to create my first program to test the implementation of Message Authentication Code (MAC). I am trying to use the HMACSHA1 hash function. My (Java 1.4) program runs fine on a dev box (V5R4).But fails terribly on the QA box (V5R3). My… >>> More
Google App Engine - Spring Security Issue (java.security.AccessControlException)

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm currently getting the AccessControlException below when I deploy to app engine (I don't see it when I run in my local environment). I'm using GAE 1.3.1, Spring 3.0.1, and Spring Security 3.0.2. Any ideas how to get around this issue? It appears to be an issue with Spring Security trying to get… >>> More