Linux Webhosting Support

Linux web hosting and server support tips

Disable greylisting completely – iRedmail

iRedMail is:
1. A ZERO COST, fully fledged, full-featured mail server solution. All components are free and open source software
2. It support unlimited domains and email accounts.
2. SpamAssassin, ClamAV, SPF, DKIM, greylisting, whitelisting, blacklisting.
3. Stores mail accounts in your favourte backend: OpenLDAP, MySQL, MariaDB, PostgreSQL.
4. Supports major Linux distros

You know how difficult is to configure a fully fledged email service you have tried. iRedmail do this heavy part for you. I would recommend this piece of software to everyone. I used to configure email server manually using Postfix, Postfixadmin, MySQL, SpamAssassin, etc. Even though I have done this several times, it needs 2-3 hours for setup. But iRedmail can do all of this and MORE in few minutes, thus saves lot of time.

How to disable greylisting completely

Greylisting is a method of defending e-mail users against spam. A mail transfer agent (MTA) using greylisting will “temporarily reject” any email from a sender it does not recognize

To disable greylisting completely, please remove plugin name greylisting in iRedAPD config file
/opt/iredapd/settings.py, parameter plugins =:
plugins = […, ‘greylisting’, …]

Restarting iRedAPD service is required.

Reject outgoing Spam – iRedmail server

iRedMail is:
1. A ZERO COST, fully fledged, full-featured mail server solution. All components are free and open source software
2. It support unlimited domains and email accounts.
2. SpamAssassin, ClamAV, SPF, DKIM, greylisting, whitelisting, blacklisting.
3. Stores mail accounts in your favourte backend: OpenLDAP, MySQL, MariaDB, PostgreSQL.
4. Supports major Linux distros

You know how difficult is to configure a fully fledged email service you have tried. iRedmail do this heavy part for you. I would recommend this piece of software to everyone. I used to configure email server manually using Postfix, Postfixadmin, MySQL, SpamAssassin, etc. Even though I have done this several times, it needs 2-3 hours for setup. But iRedmail can do all of this and MORE in few minutes, thus saves lot of time.

Reject outgoing Spam

iRedmail comes with Amavis, Spamassasin and Clamd. By default iRedmail will not block Outgoing spam message. However you can tweak Amavis configurations to reject such mails.

/etc/amavisd/amavisd.conf

Add following to $policy_bank{‘ORIGINATING’}

final_virus_destiny => D_DISCARD,
final_banned_destiny => D_REJECT,
final_spam_destiny => D_REJECT,
final_bad_header_destiny => D_REJECT,

Then restart amavis /etc/init.d/amavisd restart

This will reject all outgoing spam mails above the score

Of course tweak the spam score accordingly.

URL Monitoring With Nagios

Capabilities

Nagios provides complete URL monitoring of HTTP and HTTPS servers and protocols as well as full URL transaction monitoring.

Benefits

Implementing effective URL monitoring with Nagios offers the following benefits:
* Increased server, services, and application availability
* Fast detection of network outages and protocol failures
* Monitor user experience when accessing URLs
* Web server performance monitoring
* Web transaction monitoring
* URL monitoring

URL monitoring

By using the ‘check_http’ nagios command, we can monitor a specific url rather than checking the Apache service is up or not. This method is helpful to identify if the website is hacked and url is injected with malicious codes or there is some Apache or php errors and page is throwing an error instead. The normal Apache service check will return successful results in the above case.
We can check for a specific keyword string on the webpage. If that string not present, an error will be returned.

Here is an real example

define service{
    use                            urlmonitoring-service
    host_name                      server.linuxwebservertips.in
    service_description            url_check
    check_command                  check_http!-H linuxwebservertips.in -t 30 -R "Cpanel and WHM" -f follow
}

The above will check for the keyword “Cpanel and WHM” on the page “linuxwebservertips.in”. If the keyword is missing or the page is not responding nagios will retun and error.

URL monitoring +SSL

You can refer to below example if the web page has SSL/TLS enabled.

define service{
    use                            urlmonitoring-service
    host_name                      server.linuxwebservertips.in
    service_description            url_check
    check_command                  check_http!-H linuxwebservertips.in -t 30 -R "Cpanel and WHM" -f follow --ssl
}

Here we added the option “–ssl” to the check command

URL monitoring on ht password protected page

Normal method will not work as we need to validate ht password protection first to see the page. You can use the following example for such pages.

define service{
    use                            urlmonitoring-service
    host_name                      server.linuxwebservertips.in
    service_description            url_check_protected
    check_command                  check_http!-H linuxwebservertips.in -a user:password -t 30 -R "Cpanel and WHM" -f follow --ssl 
}

Replace the username and password appropriately.

Run Postfix on multiple ports

Adding additional SMTP listenerports

By default postfix run on port 25 and 587(TLS). However some ISPs block port 25. In that case you can configure the postfix mail server to listen on addional ports too, for example port 26 or some random 5125.

This configuration is done in the master.cf configuration file. Edit it in your editor of choice.

This file is in the following format:

# ==========================================================================
# service type private unpriv chroot wakeup maxproc command + args
# (yes) (yes) (yes) (never) (100)
# ==========================================================================

The first column is the port number that you want to listen on. The default SMTP port 25 line will read as follows:

smtp inet n - - - - smtpd

To add an additional listener port of 5125, insert the the following after the above:

5125 inet n - n - - smtpd

Save the file and restart postfix service

service postfix restart

Now you can use port 25, 587 and 5125 to connect to your mail server.

FTP connectivity problem:: No route to host

FTP connectivity problem

If you are getting following error while FTP directory listing, follow the solution provided below

———-
ftp> ls
227 Entering Passive Mode (108,61,169,245,167,161).
ftp: connect: No route to host
———-

Solution

Edit /etc/sysconfig/iptables-config and add this line:

IPTABLES_MODULES=”ip_conntrack_ftp”

Save it and restart iptables.
That’s because passive mode use non standard ports to communicate, so you need to keep trak of the ftp connections and iptables will allow them when necessary.

However, you will need to do this every time you reboot your RedHat server. Thus as a more permanent solution you can persistently load this module after each reboot by creating executable shell script within /etc/sysconfig/modules/ directory. Create file /etc/sysconfig/modules/iptables.modules with the following content:

#!/bin/sh
exec /sbin/modprobe ip_conntrack_ftp >/dev/null 2>&1

Once you save this file you also need to make it executable:
# chmod +x /etc/sysconfig/modules/iptables.modules

Another solution is specify the passive ports that will be used on FTP server configuration, then open those specific ports on firewall.

Plesk update error/autoinstaller error

If you are getting the below error while updating the Plesk versions or installing the microupdates

—-
ERROR: Unable to download the MD5 sum for the new Parallels Installer binary.
Not all packages were installed.
Please, contact product technical support.
—-

Solution
—–
Remove cache from /var/cache/parallels_installer/ and start autoinstaller again.
/usr/local/psa/admin/sbin/autoinstaller –select-product-id plesk –select-release-current –reinstall-patch –install-component base
—–

CSR generation for UCC certificates

Unified Communications (UC) Certificates (also called SAN Certificates) use Subject Alternative Names o secure multiple sites (e.g. fully qualified domain names) with one certificate. Four SANs are included in the base price of the UC Certificate, but you can purchase additional names at any time during the lifetime of the certificate.

With a UC Certificate, you can secure:

www.linuxwebservertips.in
www.example2.com
www.example3.net
mail.example.net
dev.example2.com

The CSR generation process is little different for creating an UCC certificates. We will have to create a Openssl based configuration file and then create private key and CSR from it.

Step 1: Create a custom OpenSSL Conf file.

The following is an example conf file that can be used for creation of a SAN/UCC cert. Save it as multissl.conf

———–
[ req ]
default_bits = 2048
default_keyfile = privkey.pem
distinguished_name = req_distinguished_name
req_extensions = req_ext # The extentions to add to the self signed cert

[ req_distinguished_name ]
countryName = Country Name (2 letter code)
countryName_default = US
stateOrProvinceName = State or Province Name (full name)
stateOrProvinceName_default = Iowa
localityName = Locality Name (eg, city)
localityName_default = Iowa City
organizationName = Organization Name (eg, company)
organizationName_default = The University of Iowa
organizationalUnitName = Organizational Unit Name (eg, section)
organizationalUnitName_default = Domain Control Validated
commonName = Common Name (eg, YOUR SSL domain name)
commonName_max = 64

[ req_ext ]
subjectAltName = @alt_names

[alt_names]
DNS.1 = www.linuxwebservertips.in
DNS.2 = www.example1.com
DNS.3 = example2.com
———–

Notes:

The alt_names section (DNS.1, DNS.2, ….) are the list of all other domain names you wish to secure with this cert. Additional can be added such as DNS.4, etc.
The following examples assume that you name the above config file file multissl.conf (if it is named differently you must adjust the filename in the below examples accordingly.
Step 2: Generate the Private key and CSR with OpenSSL

Execute the following OpenSSL command

$ openssl req -nodes -newkey rsa:2048 -keyout serverfqdn.key -out multidomain.csr -config multissl.conf

* Replace “serverfqdn” with the fully qualified domain name of the server (ie: sample.server.uiowa.edu). Note: it may also be helpful to add a year to the filename.

You will then see output and be prompted for configuration as seen in the following example. Enter your details accordingly.

——————————————
$ openssl req -nodes -newkey rsa:2048 -keyout serverfqdn.key -out multidomain.csr -config multissl.conf
Generating a 2048 bit RSA private key
………………………………….+++
…………………………………………………………+++
writing new private key to ‘serverfqdn.key’
—–
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter ‘.’, the field will be left blank.
—–
Country Name (2 letter code) [US]:US
State or Province Name (full name) [Iowa]:Iowa
Locality Name (eg, city) [Iowa City]:Iowa City
Organization Name (eg, company) [The University of Iowa]:My Company name
Organizational Unit Name (eg, section) [Domain Control Validated]:IT SUPPORT
Common Name (eg, YOUR SSL domain name) []:www.linuxwebservertips.in
——————————————

Note: Replace www.linuxwebservertips.in with the “primary” domain name you want secured with this certificate (likely, but not necessarily the hostname of the machine).

At this point you should have the new key file, and CSR. Save the key file in a secure place, it will be needed to apply the new certificate. The CSR can now be submitted to request the SSL Cert.

Strong TLS/SSL Security on your server

SSL Report : www.linuxwebservertips.in

ssllab

 

 

 

 

This is a simple guide for setting up a strong TLS/SSL configuration on your server.

If you configure a web server’s TLS configuration, you have primarily to take care of three things:

1. disable SSL 2.0 (FUBAR) and SSL 3.01 (POODLE),
2. disable TLS 1.0 compression (CRIME),
3. disable weak ciphers (DES, RC4), prefer modern ciphers (AES), modes (GCM), and protocols (TLS 1.2).

 

Your Server’s Certificate

Let’s start with your digital certificate, which is at the core of HTTPS. The certificate enables clients to verify the identity of servers, through a chain of trust from your server’s certificate through intermediate certificates and up to a root certificate trusted by users’ browsers. Your server certificate should be 2048 bits in length. Using 4096 bit certificate is more secure however it require more computation times and hence slow compared to 2048 bit certs.

 

Basic HTTPS Setup

Here are basic SSL configurations, first for Apache:

;
...
SSLEngine on
SSLCertificateFile /etc/ssl/certs/your_cert
SSLCertificateChainFile /etc/ssl/certs/chained_certs
SSLCertificateKeyFile /etc/ssl/certs/your_private_key
<;/VirtualHost>;

And then for Nginx:

server {
...
ssl on;
ssl_certificate /etc/ssl/certs/your_cert_with_chain;
ssl_certificate_key /etc/ssl/certs/your_private_key;
ssl_session_cache shared:SSL:50m;
ssl_session_timeout 10m;
}

In Nginx, the ssl_certificate parameter is confusing. It expects your certificate plus any necessary intermediate certificates, concatenated together.

Make sure all of these files are at least mode 0444, except your private key, which should be 0400.

 

Software versions

On the server side you should update your OpenSSL to 1.0.1c+ so you can support TLS 1.2, GCM, and ECDHE as soon as possible. Fortunately that’s already the case in Ubuntu 12.04 and later.

On the client side the browser vendors are starting to catch up. As of now, Chrome 30, Internet Explorer 11 on Windows 8, Safari 7 on OS X 10.9, and Firefox 26 all support TLS 1.2.

 

Cipher Suite Configuration

The recommended cipher suites for Apache are follows

SSLCipherSuite EECDH+AESGCM:EDH+AESGCM:AES256+EECDH:AES256+EDH
SSLHonorCipherOrder on

The recommended cipher suite for backwards compatibility (IE6/WinXP):

SSLCipherSuite EECDH+AESGCM:EDH+AESGCM:AES256+EECDH:AES256+EDH:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-SHA384:ECDHE-RSA-AES128-SHA256:ECDHE-RSA-AES256-SHA:ECDHE-RSA-AES128-SHA:DHE-RSA-AES256-SHA256:DHE-RSA-AES128-SHA256:DHE-RSA-AES256-SHA:DHE-RSA-AES128-SHA:ECDHE-RSA-DES-CBC3-SHA:EDH-RSA-DES-CBC3-SHA:AES256-GCM-SHA384:AES128-GCM-SHA256:AES256-SHA256:AES128-SHA256:AES256-SHA:AES128-SHA:DES-CBC3-SHA:HIGH:!aNULL:!eNULL:!EXPORT:!DES:!MD5:!PSK:!RC4
SSLHonorCipherOrder on

 

And here’s the same configuration for Nginx:

ssl_ciphers 'EECDH+AESGCM:EDH+AESGCM:AES256+EECDH:AES256+EDH';
ssl_prefer_server_ciphers on;

The recommended cipher suite for backwards compatibility (IE6/WinXP):

ssl_ciphers "EECDH+AESGCM:EDH+AESGCM:AES256+EECDH:AES256+EDH:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-SHA384:ECDHE-RSA-AES128-SHA256:ECDHE-RSA-AES256-SHA:ECDHE-RSA-AES128-SHA:DHE-RSA-AES256-SHA256:DHE-RSA-AES128-SHA256:DHE-RSA-AES256-SHA:DHE-RSA-AES128-SHA:ECDHE-RSA-DES-CBC3-SHA:EDH-RSA-DES-CBC3-SHA:AES256-GCM-SHA384:AES128-GCM-SHA256:AES256-SHA256:AES128-SHA256:AES256-SHA:AES128-SHA:DES-CBC3-SHA:HIGH:!aNULL:!eNULL:!EXPORT:!DES:!MD5:!PSK:!RC4";
ssl_prefer_server_ciphers on;

If your version of OpenSSL is old, unavailable ciphers will be discarded automatically. Always use the full ciphersuite above and let OpenSSL pick the ones it supports.

The ordering of a ciphersuite is very important because it decides which algorithms are going to be selected in priority. The recommendation above prioritizes algorithms that provide perfect forward secrecy.

 

Prioritization logic

ECDHE+AESGCM ciphers are selected first. These are TLS 1.2 ciphers and not widely supported at the moment. No known attack currently target these ciphers.
PFS ciphersuites are preferred, with ECDHE first, then DHE.
AES 128 is preferred to AES 256.  At the moment, AES128 is preferred, because it provides good security, is really fast, and seems to be more resistant to timing attacks.
In the backward compatible ciphersuite, AES is preferred to 3DES. BEAST attacks on AES are mitigated in TLS 1.1 and above, and difficult to achieve in TLS 1.0. In the non-backward compatible ciphersuite, 3DES is not present.
RC4 is removed entirely. 3DES is used for backward compatibility

 

Protocol Support: SSL or no SSL

To prevent downgrade attacks and poodle attack, we will also disable old SSL protocols

For Apache:

SSLProtocol all -SSLv2 -SSLv3

For Nginx:

ssl_protocols TLSv1 TLSv1.1 TLSv1.2;

This disables all versions of SSL, enabling only TLS 1.0 and up. All versions of Chrome and Firefox support at least TLS 1.0.

How to Disable SSLv3 for Apache,Nginx, Litespeed, cPanel

The POODLE bug is a new bug discovered by Google in the SSLv3 protocol. The fix is easy, disable support for SSLv3.

See the google security blog for more info on the bug: http://googleonlinesecurity.blogspot.nl/2014/10/this-poodle-bites-exploiting-ssl-30.html.

 

Fix POODLE

To fix the bug, disable SSLv3 and use a secure cipherlist. SSL v2 is also insecure, so we need to disable it too.

So edit the Apache config file and add following

SSLProtocol All -SSLv2 -SSLv3

All is a shortcut for +SSLv2 +SSLv3 +TLSv1 or – when using OpenSSL 1.0.1 and later – +SSLv2 +SSLv3 +TLSv1 +TLSv1.1 +TLSv1.2, respectively. The above line enables everything except SSLv2 and SSLv3

And then restart the Apache service

service httpd restart

 

cPanel/WHM

If you have a cPanel server, you should not edit Apache configurations directly, instead you can do this from WHM.

 

Apache-Configuration-WHM

 

1. Visit your server’s WHM Panel ( https://<yourserversip>:2087 )
2. Navigate to the Apache Configuration Panel of WHM.
3. Scroll down to the ‘Include Editor’ Section of the Apache Configuration.
4. Click ‘Pre Main Include’, which will jump to the corresponding section. Via the drop-down selector, choose ‘All Versions’.
5. An empty dialogue box will appear allowing you to input the needed configuration updates. In this box, copy and paste the following:

SSLProtocol All -SSLv2 -SSLv3
SSLHonorCipherOrder On

 

For Nginx

If you’re running an NGINX web server that currently uses SSLv3, you need to edit the NGINX configuration (nginx.conf). You will need to add the following line to your server directive:

ssl_protocols TLSv1 TLSv1.1 TLSv1.2;

Then restart the nginx service

service nginx restart

For LiteSpeed:

Update to LiteSpeed version 4.2.18.

For more information about Litespeed & POODLE: http://www.litespeedtech.com/support/forum/threads/lsws-4-2-18-released-%E2%80%94-addresses-poodle-sslv3-vulnerability.9948/

Note about Mail Servers:

The POODLE attack requires the client to retry connecting several times in order to downgrade to SSLv3, and typically only browsers will do this. Mail Clients are not as susceptible to POODLE. However, users who want better security should switch to Dovecot until we upgrade Courier to a newer version.

For cpsrvd:

1. Go to WHM => Service Configuration => cPanel Web Services Configuration
2. Make sure that the “TLS/SSL Protocols” field contains “SSLv23:!SSLv2:!SSLv3”.
3. Select the “Save” button at the bottom.

For cpdavd:

1. Go to WHM => Service Configuration => cPanel Web Disk Configuration
2. Make sure that the “TLS/SSL Protocols” field contains “SSLv23:!SSLv2:!SSLv3”.
3. Select the “Save” button at the bottom.

For Dovecot:

1. Go to WHM => Service Configuration => Mailserver Configuration.
2. SSL Protocols should contain “!SSLv2 !SSLv3”. If it does not, replace the text in this field.
3. Go to the bottom of the page, and select the Save button to restart the service.

For Courier:

Courier has released a new version to mitigate this as of 10/22, until we have an opportunity to review, test, and publish the new version of Courier please switch to Dovecot for enhanced security.

For Exim:

1. Go to Home » Service Configuration » Exim Configuration Manager
2. Under Advanced Editor, look for ‘openssl_options’.
3. Make sure the field contains “+no_sslv2 +no_sslv3”.
4.Go to the bottom of the page, and select the Save button to restart the service.

 

For Lighttpd:

Lighttpd releases before 1.4.28 allow you to disable SSLv2 only.

If you are running at least 1.4.29, put the following lines in your configuration file:

ssl.use-sslv2 = "disable"
ssl.use-sslv3 = "disable"

How to verify the Poodle is disabled

You can use a website like http://poodlebleed.com/ for a web based check.

 

Manual check

To make sure services on your server are not accepting SSLv3 connections, you can run the openssl client on your server against the SSL ports. This command is run as follows:

openssl s_client -connect linuxwebservertips.in:443 -ssl3

If it fails (which is what you want), you should see something like this at the top of the output:

3078821612:error:14094410:SSL routines:SSL3_READ_BYTES:sslv3 alert handshake failure:s3_pkt.c:1257:SSL alert number 40
3078821612:error:1409E0E5:SSL routines:SSL3_WRITE_BYTES:ssl handshake failure:s3_pkt.c:596:

Shellshock How to check if you are vulnerable

A new vulnerability has been found that potentially affects most versions of the Linux and Unix operating systems, in addition to Mac OS X. Known as the “Bash Bug” or “ShellShock,” the GNU Bash Remote Code Execution Vulnerability could allow an attacker to gain control over a targeted computer if exploited successfully. And because Bash is everywhere on Linux and UNix-like machines and interacts with all parts of the operating system, everyone anticipates that it will have lot of repercussions.

How does Shellshock work?

Shellshock exploits a flaw in how Bash parses environment variables; Bash allows functions to be stored in environment variables, but the issue is Bash will execute any code placed after the function in the environment variable value.

For example, an environment variable setting of VAR=() { ignored; }; /bin/id will execute /bin/id when the environment is imported into the bash process.

I am vulnerable?

You can check if you’re vulnerable by running the following lines in your default shell.

env X=”() { :;} ; echo vulnerable” `which bash` -c “echo Check completed”

If you see the word “vulnerable” echo’d back , then you’re at risk.

How Shellshock is Impacting the Web

The most likely route of attack is through Web servers utilizing CGI (Common Gateway Interface), the widely-used system for generating dynamic Web content. An attacker can potentially use CGI to send a malformed environment variable to a vulnerable Web server. The attacker is able to inject environment variables inside all bash process spawned by a web server under the CGI specification. This will occur directly if the CGI script is programmed in bash or indirectly by system calls inside other types of CGI scripts since the environment will propagate to the sub-shell. The vulnerability will automatically be triggered at the shell process instantiation. Furthermore if specific headers are used as attack points, the payload may not appear in the webserver logs, letting a compromise occur with virtually no trace of the intrusion.

Example:

CGI stores the HTTP headers in environment variables. Let’s say the example.com is running a CGI application written in Bash script.

We can modify the HTTP headers such that it will exploit the shellshock vulnerability in the target server and executes our code.

curl -k http://example.com/cgi-bin/test -H “User-Agent: () { :;}; echo Hacked > /tmp/Hacked.txt”

Here, the curl is sending request to the target website with the User-Agent containing the exploit code. This code will create a file “Hacked.txt” in the “/tmp” directory of the server.

What can I do to protect myself?

Major operating software vendors including RedHaT, CentOS, etc are already released a initial patch for this bug.

Debian—https://www.debian.org/security/2014/dsa-3032

Ubuntu—http://www.ubuntu.com/usn/usn-2362-1/

Red Hat—https://access.redhat.com/articles/1200223*

CentOS—http://centosnow.blogspot.com/2014/09/critical-bash-updates-for-centos-5.html

Novell/SUSE— http://support.novell.com/security/cve/CVE-2014-6271.html

If a patch is unavailable for a specific distribution of Linux or Unix, it is recommended that users switch to an alternative shell until one becomes available.

Need expert assistanace?

I can help you to patch your server against this bug and make sure you and your customers are secure. Mail me at therealfreelancer[at]gmail[dot]com.

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