Fix the JenkinsAPI No valid crumb error

If you are working with the Python based JenkinsAPI library you might run into the No valid crumb was included in the request error.  The error below will probably look familiar if you’ve run into this issue.

Traceback (most recent call last):
 File "myscript.py", line 47, in <module>
 deploy()
 File "myscript.py", line 24, in deploy
 jenkins.build_job('test')
 File "/usr/local/lib/python3.6/site-packages/jenkinsapi/jenkins.py", line 165, in build_job
 self[jobname].invoke(build_params=params or {})
 File "/usr/local/lib/python3.6/site-packages/jenkinsapi/job.py", line 209, in invoke
 allow_redirects=False
 File "/usr/local/lib/python3.6/site-packages/jenkinsapi/utils/requester.py", line 143, in post_and_confirm_status
 response.text.encode('UTF-8')
jenkinsapi.custom_exceptions.JenkinsAPIException: Operation failed. url=https://jenkins.example.com/job/test/build, data={'json': '{"parameter": [], "statusCode": "303", "redirectTo": "."}'}, headers={'Content-Type': 'application/x-www-form-urlencoded'}, status=403, text=b'<html>\n<head>\n<meta http-equiv="Content-Type" content="text/html;charset=utf-8"/>\n<title>Error 403 No valid crumb was included in the request</title>\n</head>\n<body><h2>HTTP ERROR 403</h2>\n<p>Problem accessing /job/test/build. Reason:\n<pre> No valid crumb was included in the request</pre></p><hr><a href="http://eclipse.org/jetty">Powered by Jetty:// 9.4.z-SNAPSHOT</a><hr/>\n\n</body>\n</html>\n'

It is good practice to enable additional security in Jenkins by turning on the “Prevent Cross Site Forgery exploits” option in the security settings, so if you see this error it is a good thing.  The below example shows this security feature in Jenkins.

enable xss protection

The Fix

This error threw me off at first, but it didn’t take long to find a quick fix.  There is a crumb_requester class in the jenkinsapi that you can use to create the crumbed auth token.  You can use the following example as a guideline in your own code.

from jenkinsapi.jenkins import Jenkins
from jenkinsapi.utils.crumb_requester import CrumbRequester

JENKINS_USER = 'user'
JENKINS_PASS = 'pass'
JENKINS_URL = 'https://jenkins.example.com'

# We need to create a crumb for the request first
crumb=CrumbRequester(username=JENKINS_USER, password=JENKINS_PASS, baseurl=JENKINS_URL)

# Now use the crumb to authenticate against Jenkins
jenkins = Jenkins(JENKINS_URL, username=JENKINS_USER, password=JENKINS_PASS, requester=crumb)

...

The code looks very similar to creating a normal Jenkins authentication object, the only difference being that we create and then pass in a crumb for the request, rather than just a username/password combination.  Once the crumbed authentication object has been created, you can continue writing your Python code as you would normally.  If you’re interested in learning more about crumbs and CSRF you can find more here, or just Google for CSRF for more info.

This issue was slightly confusing/annoying, but I’d rather deal with an extra few lines of code and know that my Jenkins server is secure.

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Enable SSL for your WordPress blog

Updated: 11/18/16

The Let’s Encrypt client was recently renamed to “certbot”.  I have updated the post to use the correct name but if I miss something use certbot or let me know.

With the announcement of the public beta of the Let’s Encrypt project, it is now nearly trivial to get your site set up with an SSL certificate.  One of the best parts about the Let’s Encrypt project is that it is totally free, so there is pretty much no reason to protect your blog set up with an SSL certificate.  The other nice part of Let’s Encrypt is that it is very easy to get your certificate issued.

The first step to get started is grabbing the latest source code from GitHub for the project.  Log on to your WordPress server (I’m running Ubuntu) and clone the repo.  Make sure to install git if you haven’t already.

git clone https://github.com/letsencrypt/certbot.git

There is a shell script you can run to pretty much do everything for you, including installation of any packages and libraries it needs as well as configures paths and other components it needs to work.

cd certbot
./certbot-auto

After the bootstrap is done there should be some CLI options.  Run the command with the -h flag to print out help.

./certbot-auto -h

Since I am using Apache for my blog I will use the “–apache” option.

./certbot-auto --apache

There will be some prompts you need to go through for setting up the certificates and account creation.

let's encrypt

 

 

 

 

 

This process is still somewhat error prone, so if you make a typo you can just rerun the “./letsencrypt-auto” command and follow the prompts.

The certificates will be dropped in to /etc/letsencrypt/live/<website>.  Go double check them if needed.

This process will also generate a new apache configuration file for you to use.  You can check for the file in /etc/apache2/site-enabled.  The import part of this config should look similar to the following:

<VirtualHost *:443>
  UseCanonicalName Off
  ServerAdmin [email protected]
  DocumentRoot /var/www/wordpress
  SSLCertificateFile /etc/letsencrypt/live/thepracticalsysadmin.com/cert.pem
  SSLCertificateKeyFile /etc/letsencrypt/live/thepracticalsysadmin.com/privkey.pem
  Include /etc/letsencrypt/options-ssl-apache.conf
  SSLCertificateChainFile /etc/letsencrypt/live/thepracticalsysadmin.com/chain.pem
</VirtualHost>

As a side note, you will probably want to redirect non https requests to use the encrypted connection.  This is easy enough to do, just go find your .htaccess file (mine was in /var/www/wordpress/.htaccess) and add the following rules.

<IfModule mod_rewrite.c>
  RewriteEngine On
  RewriteCond %{SERVER_PORT} 80
  RewriteRule ^(.*)$ https://example.com/$1 [R,L]
</IfModule>

Before we restart Apache with the new configuration let’s run a quick configtest to make sure it all works as expected.

apachectl configtest

If everything looks okay in the configtest then you can reload or restart apache.

service apache2 restart

Now when you visit your site you should get the nice shiny green lock icon on the address bar.  It is important to remember that the certificates issued by the Let’s Encrypt project are valid for 90 days so you will need to make sure to keep up to date and generate new certificates every so often.  The Let’s Encrypt folks are working on automating this process but for now you will need to manually generate new certificates and reload your web server.

let's encrypt

 

 

 

 

 

 

 

 

 

 

 

 

 

 

That’s it.  Your site should now be functioning with SSL.

Updating the certificate automatically

To take this process one step further We can make a script that can be run via cron (or manually) to update the certificate.

Here’s what the script looks like.

#!/usr/bin/env bash

dir="/etc/letsencrypt/live/example.com"
acme_server="https://acme-v01.api.letsencrypt.org/directory"
domain="example.com"
https="--standalone-supported-challenges tls-sni-01"

# Using webroot method
#/root/letsencrypt/certbot-auto --renew certonly --server $acme_server -a webroot --webroot-path=$dir -d $domain --agree-tos

# Using standalone method
service apache2 stop
# Previously you had to specify options to renew the cert but this has been deprecated
#/root/letsencrypt/certbot-auto --renew certonly --standalone $https -d $domain --agree-tos
# In newer versions you can just use the renew command
/root/letsencrypt/certbot-auto renew --quiet
service apache start

Notice that I have the “webroot” method commented out.  I run a service (Varnish) on port 80 that proxies traffic but also interferes with LE so I chose to run the standalone renewal method.  It is pretty easy, the main difference is that you need to turn off Apache before you run it since Apache binds to to ports 80/443.  But the downtime is okay in my case.

I chose to put the script in to a cron job and have it run every 45 days so that I don’t have to worry about logging on to my server to regenerate the certificate.  Here’s what a sample crontab for this job might look like.

0 0 */45 * * /root/renew_cert.sh

This is a straight forward process and will help with your search engine juices as well.

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Patching CVE-6271 (shellshock) with Chef

If you haven’t heard the news yet, a recently disclosed vulnerability has been released that exploits environmental variables in bash.  This has some far reaching implications because bash is so widespread and runs on many different types of devices, for example network gear, routers, switches, firewalls, etc.  If that doesn’t scare you then you probably don’t need to finish reading this article.  For more information you can check out this article that helped to break the story.

I have been seeing a lot “OMG the world is on fire, patch patch patch!” posts and sentiment surrounding this recently disclosed vulnerability, but basically have not seen anybody taking the time to explain how to patch and fix this issue.  It is not a difficult fix but it might not be obvious to the more casual user or those who do not have a sysadmin or security background.

Debian/Ubuntu:

Use the following commands to search through your installed packages for the correct package release.  You can check the Ubuntu USN for versions.

dpkg -l | grep '^ii' or
dpkg-query --show bash

If you are on Ubuntu 12.04 you will need update to the following version:

bash    4.2-2ubuntu2.3

If you are on Ubuntu 13.10, and have this package (or below), you are vulnerable.  Update to 14.04!

 bash 4.2-5ubuntu3

If you are on Ubuntu 14.04, be sure to update to the most recently patched patch.

bash 4.3-7ubuntu1.3

Luckily, the update process is pretty straight forward.

apt-get update
apt-get --only-upgrade install bash

If you have the luxury of managing your environment with some sort of automation or configuration management tool (get this in place if you don’t have it already!) then this process can be managed quite efficiently.

It is easy to check if a server that is being managed by Chef has the vulnerability by using knife search:

knife search node 'bash_shellshock_vulnerable:true'

From here you could createa a recipe to patch the servers or fix each one by hand.  Another cool trick is that you can blast out the update to Debian based servers with the following command:

knife ssh 'platform_family:debian' 'sudo apt-get update; sudo apt-get install -y bash'; knife ssh 'platform_family:redhat' 'sudo yum -y install bash'

This will iterate over every server in your Chef server environment that is in the Debain family (including Ubuntu) or RHEL family (including CentOS) and update the server packages so that the latest patched bash version gets pulled down and then gets updated to the latest version.

You may need to tweak the syntax a little, -x to override the ssh user and -i to feed an identity file.  This is so much faster than manually installing the update on all your servers or even fiddling around with a tool like Fabric, which is still better than nothing.

One caveat to note:  If you are not on an LTS version of Ubuntu, you will need to upgrade your server(s) first to an LTS, either 12.04 or 14.04 to qualify for this patch.  Ubuntu 13.10 went out of support in August which was about a month ago as per the time of this writing so you will want to get your OS up date.

One more thing:  The early patches to address this vulnerability did not entirely fix the issue, so make sure that you have the correct patch installed.  If you patched right away there is a good chance you may still be vulnerable, so simply rerun your knife ssh command to reapply the newest patch, now that the dust is beginning to settle.

Outside of this vulnerability, it is a good idea to get your OS on an Ubuntu LTS version anyway to continue receiving critical updates for software as well as security patches for a longer duration than the normal, 6 month release cycle of the server distribution.

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Set up PEM key authentication

Many times it is useful to keys to authenticate to your servers.  This can dramatically improve security and is a great way to manage servers in bulk as well.  You just need to keep track of your keys rather than having to remember a large number of passwords.  The steps to get PEM key authentication are fairly straight forward but it never hurts to walk through the process of getting them set up correctly.

Side Note: I’d like to also mention briefly, that I have these steps set up to work with Chef, so every server that gets deployed using Chef will use PEM keys out of the box, which works out very nicely.  If you’re interested I can expound on that topic a little more, just let me know.

The first step in the process is to generate some keys using openssl.  If you don’t have openssl go download and install it.  If you do have openssl but haven’t updated in ahwile, please update to avoid the heartbleed vulnerability that was recently exploited (nearly all distributors have released the patched version at this point so it should be trivial).

We want to generate our key and create a PEM file out of it.  Here are the steps:

cd ~/.ssh
ssh-keygen -t dsa -b 1024
openssl dsa -in id_dsa -outform pem > test.pem
cat ida_dsa >> authorized_keys

You can leave the values blank (default) in the ssh-keygen.

Now you should have similar listings in your ~/.ssh directory:

ssh keys

  • authorized_keys – This is the public key that the pem file gets authenticated against
  • id_dsa – This is the private portion of the key that we generated in the steps above
  • id_dsa.pub – This is the public key section that is used when authenticating
  • test.pem – this is the file that will be used to authenticate.  Essentially the private key minus the pass phrase

Now you just need to copy the test.pem file that was just generated to a different host in order to log in with your PEM key using scp or rsync.  Once that is done, the command to connect to the remote host using  your key should look similar to the following:

ssh -i /path/to/pem [email protected]

Next steps.  At this point you should have a working pem authentication on your server.  It is probably a good idea at this point to start looking at hardening the security as well as the SSH configuration on the host.  Small things can go a long way.  For example disabling root login, disabling password authentication, etc. will stop a very large amount of attacks from hitting your server now that you are authenticating with pem keys.

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Using a self signed cert with Nginx

After the recent heart bleed incident (which I’m sure many of you well remember) I had to reassign some certificates. It turns out that this was a great opportunity to create a blog post.  Since I do not create and assign certs very frequently it is a good opportunity to take some notes and hopefully ease the process for others.  After patching the vulnerable version of Openssl, there are really only a few steps needed to accomplish this.  Assuming you already have nginx installed, which is trivial to do on Ubuntu, the first step is to create the necessary crt and key files.

sudo openssl req -x509 -nodes -days 365 -newkey rsa:2048 -keyout /etc/nginx/cert.key -out /etc/nginx/cert.crt

Next you will need to tell nginx to load up you new certs in its config.  Here is an example of what the server block in you /etc/nginx/site-available config might look like.  Notice the ssl_certificate and ssl_certificate_key files correspond to the cert files we created above, which we stuck in the /etc/nginx directory.  If you decide to place these certs in a different location you will need to modify your config file to reflect the location.

server {

listen *:443; 
ssl on; 
ssl_certificate cert.crt; 
ssl_certificate_key cert.key; 
ssl_session_timeout 5m; 
ssl_protocols SSLv3 TLSv1; 
ssl_ciphers ALL:!ADH:!EXPORT56:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv3:+EXP; 
ssl_prefer_server_ciphers on;

}

Just to cover all our bases here we will also redirect any requests that come in to port 80 (default web) back to 443 for ssl.  The is a simple addition and will add an additional layer of security.

server { 
listen 80; 
return 301 https://$host$request_uri; 
}

The final step is to reload your configuration and test to make sure everything works.

sudo service nginx reload

If your nginx fails to reload, more than likely there is some sort of configuration or syntax error in your config file.  Comb through it for any potential errors or mistakes.  Once your config is loaded properly you can check your handy work by attempting to hit your site using http://.  If your config is working properly it should automatically redirect you to https://.

That’s all it takes.  I think it might be a good exercise to try something like this with Chef but for now this process works okay by hand.  Let me know what you think or if this can be improved.

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