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Secure Memcached on Directadmin server

| 14:20:23 01.03.2018

CloudFlare reported in their blog-post about a big increase in an obscure amplification attack vector - using the memcached protocol, coming from UDP port 11211. Here we will provide details on how to protect your server with Directadmin.

What you have?

By default memcached on a CentOS server is accepting connections from all IPs to port 11211 both TCP and UDP:

# netstat -nlp | grep memcached
tcp        0      0     *                   LISTEN      11287/memcached
tcp        0      0 :::11211                    :::*                        LISTEN      11287/memcached
udp        0      0     *                               11287/memcached
udp        0      0 :::11211                    :::*                                    11287/memcached

What to do?

First of all make sure you've a firewall which is filtering incoming and outgoing connections to port 11211.

Then update memcached options in the file /etc/sysconfig/memcached. Originally it looks like:


So we need to update OPTIONS to the following view:

OPTIONS=" -l -U 0"

Now restart memcached and check results:

[root@server ~]#  netstat -nlp | grep memc
tcp        0      0   *                   LISTEN      11871/memcached
[root@server ~]# 

That's it.

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We are a team of professionals, and specialize in installation, configuring and managing of remote virtual and dedicated servers powered by Linux/Unix-like OS with DirectAdmin. We support various sets of software, including web-servers Apache, Nginx; internet domain name servers Bind, PowerDNS; mail-servers with POP3, IMAP and SMTP, FTP-servers, etc. After years of working through the most complex server challenges our team has gathered valuable experience and universal solutions suitable for everyday tasks. We are here to lend you a helping hand and take care of your servers in order to let you have enough time to do more of what you love.

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