Posts Tagged ‘CentOS’

vsftpd, FTPES & CentOS 5.5 part 1

Ask anyone that knows me and they’ll tell you I love Linux. In particular, I love Red Hat’s flavor of Linux. I’ve still got my first Linux book “The Complete Red Hat 5.2 Installation Guide” and while I don’t consult it first for all problems I do remember thumbing thru its pages when trying to configure those tulip.o drivers and how to change my X Windows config file settings (NOTE: I still to this day get tripped up on configuring X Windows!) So that having been said, it’s no wonder I’m using CentOS and have been for years since Red Hat has stopped releasing a free desktop variety for users to use (I know they’ve got Fedora but that product lines’ release cycle is too aggressive for my tastes.) 

  So that having been said, I love CentOS. I’ve been using it at home for a while now and whenever possible do my best to stick w/ the stock rpms so updates go smoothly. I’ve recently been trying to get vsftpd daemon to use encryption while still jailing my end users in their home directories and here’s what I found out. Vsftpd doesn’t natively do sftp but it does do ftpes pretty well. So I’m going to walk thru generating a private key, making a certificate signing request, adding the public key from your third party certificate authority (CA) to their certificate bundle to form a chained public key and finally, configuring vsftpd to do ftpes.

First, I logged into the box and grabbed superuser.

su -

Then changed directory to the location of the certificates.

cd /etc/pki/tls/certs/

Next, I ran openssl to generate my private key w/o a passphrase! (NOTE: If you decide to use a passphrase a number of services won’t auto start on a power failure which means you’ll need to run home, start the service manually again and enter in the passphrase so the service can use the certificate. Some services can be configured to manually put the passphrase in for you but that’s lots of effort.)

openssl genrsa -out myserver.mydomain.private.key 2048

Had I wanted to generate a private key w/ a passphrase it would have been…

openssl genrsa -des3 -out myserver.mydomain.private.key 2048

You’ll notice at the end of the command I put 2048. That stands for how many bits this certificate is generated with. A number of CAs will require now a days that you use a 2048 bit key versus the old standby of 1024 bit ( the CA I use GoDaddy is one of them.)

The very next thing we need to do is lock down your private key. This is used to encode encrypted communications to the end user who will now use your public key to decrypt the data. So let’s make it readable only by root.

chmod 600 myserver.mydomain.private.key

Once that’s done, it’s time to generate our certificate signing request (CSR) that needs to be passed to your CA so they can generate a public certificate for you.

openssl req -new -key myserver.mydomain.private.key -out myserver.csr

At this point you’ll be prompted for answers to a series of questions which will be placed in your CSR. The big thing you need to get right is your Common Name (CN) question. Make sure the CN is the server name that matches up w/ your DNS entry for this server. Folks are going to use DNS to access your server so the certificate needs to match up with what they are going to use to hit your server across the internet. It’s interesting to note, that w/ GoDaddy, pretty much all of the other fields you fill in get thrown out in the generated public certificate they send back to you so don’t get too freaked out with putting your location information in there. Again, this is with GoDaddy. Other CAs may publish that information w/ the public certificate.

After you’ve submitted your CSR to your CA. You’ll have to go thru the whole domain verification process which can be its’ own little tap dance. I know when our company had their domain names register w/ someone else besides GoDaddy it took 24 to 48 hours for whois verification and whatnot. Once we moved our domain names to GoDaddy the verification process took less that 5 minutes. Coincidence? Business strategy? I don’t know but I’m sure glad we moved our domains over to GoDaddy.

Okay, so you’ve finally gotten your certificate from your CA. Yay! Now comes the fun of lumping that certificate w/ the included CA bundle they sent you and configuring your vsftpd daemon.

First, concatenating the two files together into a combined public certificate file. Why? Cause vsftpd doesn’t have an option for the certificate chain file your CA gave you w/ your public certificate.

cat myserver.crt CA_bundle.crt > myserver.mydomain.public.key

This will put both files together into a combined file which will have all certificates. Now we can configure vsftpd and be done.

Open up the vsftpd.conf file w/ vi.

vi /etc/vsftpd/vsftpd.conf

When looking at your vsftpd.conf file I started at the beginning and slowly worked my way thru turning off features I knew I didn’t need. One of the first was anonymous_enabled. It defaults to enabled unless you uncomment the line and tell it NO. Most everything else I left as is. It’s interesting to note, that the SSL features you’re looking for in the config file aren’t present so you’ll need to add them manually to the file. Here’s what I’ve put in mine. Most of these commands by the way are covered in your man page for vsftpd.conf so take a look there for a more detailed explanation.

ssl_enable=YES
allow_anon_ssl=NO
force_local_data_ssl=YES
force_local_logins_ssl=YES
ssl_tlsv1=YES
ssl_sslv2=NO
ssl_sslv3=NO
rsa_cert_file=/etc/pki/tls/certs/myserver.mydomain.public.key
rsa_private_key_file=/etc/pki/tls/certs/myserver.mydomain.private.key

This essentially turns on SSL, turns off anonymous SSL, forces both data & logins to go over SSL and only allows TLS encryption. It also points to the location of your public & private keys.

This concluded part 1. Part 2 will talk about the implications of encrypting your FTP traffic and how it will mess w/ your FW rules at your border device.

-Q

Links I found useful while doing my install:
http://wiki.vpslink.com/Configuring_vsftpd_for_secure_connections_%28TLS/SSL/SFTP%29

http://en.wikipedia.org/wiki/FTPS

http://vsftpd.beasts.org/vsftpd_conf.html

Quickie on Dovecot. Suicidal daemon…

This post is out of sequence but I told myself I’d throw it up while it’s still fresh. About a month ago I redid my entire email server from scratch when I started having some hardware issues. This post is on one of those bug-a-boos of switching from a physical server to a virtual world. TIME. Seems keeping vmguests synchronized with the correct time is an issue and wrecks havoc upon Dovecot (even when vmware tools are installed!) So, one of solutions was to not only install the vmware tools on my vmguest but to also install ntpd. This is good and bad…

  See, ntpd checks the time rather frequently and all it takes is a sync of > 75 seconds and Dovecot kills itself. Thankfully, it left a message in the log file.

dovecot: Time just moved backwards by 109 seconds. This might cause a lot of problems, so I’ll just kill myself now. http://wiki.dovecot.org/TimeMovedBackwards: 1 Time(s)

The URL provided in the error message was very illuminating and gave some recommendations from there. I installed the script that used lsof and was pretty much good to go. I did a couple of tests to ensure it wasn’t just restarting it once per minute then did the old crontab -e command and placed the script in the root’s cron jobs file stored at /var/spool/cron/root. Life is good. I’ve always been a big fan of netstat but lsof also gives some very valuable information on tracking down rogue issues.

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