Entries tagged as security
Thursday, February 13. 2014
SSL, as I mentioned in a previous blog entry, has some issues when it comes to trust. But regardless of the problems with SSL, it is a necessary part of the security toolchain. In certain situations, however, it is possible to overcome these trust issues.
Commercial providers are not the only entities that are capable of being a Certificate Authority. In fact, anyone can become a CA and the tools to do so are available for free. Becoming your own CA is a fairly painless process, though you might want to brush up on your openSSL skills. And lest you think you can just start signing certificates and selling them to third parties, it's not quite that simple. The well-known certificate authorities have worked with browser vendors to have their root certificates added as part of the browser installation process. You'll have to convince the browser vendors that they need to add your root certificate as well. Good luck.
Having your own CA provides you the means to import your own root certificate into your browser and use it to validate certificates you use within your network. You can use these SSL certificates for more than just websites as well. LDAP, RADIUS, SMTP, and other common applications use standard SSL certificates for encrypting traffic and validating remote connections. But as mentioned above, be aware that unless a remote user has a copy of your root certificate, they will be unable to validate the authenticity of your signed certificates.
Using certificates signed by your own CA can provide you that extra trust level you may be seeking. Perhaps you configured your mail server to use your certificate for the POP and IMAP protocols. This makes it more difficult for an attacker to masquerade as either of those services without obtaining your signing certificate so they can create their own. This is especially true if you configure your mail client such that your root certificate is the only certificate that can be used for validation.
Using your own signed certificates for internal, non-public facing services provides an even better use-case. Attacks such as DNS cache poisoning make it possible for attackers to trick devices into using the wrong address for an intended destination. If these services are configured to only use your certificates and reject connection attempts from peers with invalid certificates, then attackers will only be able to impersonate the destination if they can somehow obtain a valid certificate signed by your signing certificate.
Sound good? Well, how do we go about creating our own root certificate and all the various machinery necessary to make this work? Fortunately, all of the necessary tools are open-source and part of most Linux distributions. For the purposes of this blog post, I will be explaining how this is accomplished using the CentOS 6.x Linux distribution. I will also endeavor to break down each command and explain what each parameter does. Much of this information can be found in the man pages for the various commands.
OpenSSL is installed as part of a base CentOS install. Included in the install is a directory structure in /etc/pki. All of the necessary tools and configuration files are located in this directory structure, so instead of reinventing the wheel, we'll use the existing setup.
To get started, edit the default openssl.cnf configuration file. You can find this file in /etc/pki/tls. There are a few options you want to change from their defaults. Search for the following headers and change the options listed within.
Once the openssl.cnf file is set up, the rest of the process is painless. First, switch into the correct directory.
Next, use the CA command to create a new CA.
And that's about it. The root certificate is located in /etc/pki/CA/cacert.pem. This file can be made public without compromising the security of your system. This is the same certificate you'll want to import into your browser, email client, etc. in order to validate and certificates you may sign.
Now you can start signing certificates. First you'll need to create a CSR on the server you want to install it on. The following command creates both the private key and the CSR for you. I recommend using the server name as the name of the CSR and the key.
openssl req -newkey rsa:4096 -keyout www.example.com.key -out www.example.com.csr
Once you have the CSR, copy it over to the server you're using to sign certificates. Unfortunately, the existing tools don't make it easy to merely name the CSR you're trying to sign, so we need to create our own tool. First, create a new directory to put the CSRs in.
Next, create the sign_cert.sh script in the directory we just created. This file needs to be executable.
That's all you need to start signing certificates. Place the CSR you transferred from the other server into the csr directory and use script we just created to sign it.
The script automatically renamed the newly signed certificate. In the above example, the signed certificate is in www.example.com.2014.crt. Transfer this file back to the server it belongs on and you're all set to start using it.
That's it! You're now a certificate authority with the power to sign your own certificates. Don't let all that power go to your head!
Thursday, February 6. 2014
SSL, a cryptographically secure protocol, was created by Netscape in the mid-1990's. Today, SSL, and it's replacement, TLS, are used by web browsers and other programs to create secure connections between devices across the Internet.
SSL provides the means to cryptographically secure a tunnel between endpoints, but there is another aspect of security that is missing. Trust. While a user may be confident that the data received from the other end of the SSL tunnel was sent by the remote system, the user can not be confident that the remote system is the system it claims to be. This problem was partially solved through the use of a Public Key Infrastructure, or PKI.
PKI, in a nutshell, provides the trust structure needed to make SSL secure. Certificates are issued by a certificate authority or CA. The CA cryptographically signs the certificate, enabling anyone to verify that the certificate was issued by the CA. Other PKI constructs offer validation of the registrant, indexing of the public keys, and a key revocation system. It is within these other constructs that the problems begin.
When SSL certificates were first offered for sale, the CAs spent a great deal of time and energy verifying the identity of the registrant. Often, paper copies of the proof had to be sent to the CA before a certificate would be issued. The process could take several days. More recently, the bar for entry has been lowered significantly. Certificates are now issued on an automated process requiring only that the registrant click on a link sent to one of the email addresses listed in the Whois information. This lack of thorough verification has significantly eroded the trust a user can place in the authenticity of a certificate.
CAs have responded to this problem by offering different levels of SSL certificates. Entry level certificates are verified automatically via the click of a link. Higher level SSL certificates have additional identity verification steps. And at the highest level, the Extended Validation, or EV certificate requires a thorough verification of the registrants identity. Often, these different levels of SSL certificates are marketed as stronger levels of encryption. The reality, however, is that the level of encryption for each of these certificates is exactly the same. The only difference is the amount of verification performed by the CA.
Despite the extra level of verification, these certificates are almost indistinguishable from one another. With the exception of EV certificates, the only noticeable difference between differing levels of SSL certificates are the identity details obtained before the certificate is issued. An EV certificate, on the other hand, can only be obtained from certain vendors, and shows up in a web browser with a special green overlay. The intent here seems to be that websites with EV certificates can be trusted more because the identity of the organization running the website was more thoroughly validated.
In the end, though, trust is the ultimate issue. Users have been trained to just trust a website with an SSL certificate. And trust sites with EV certificates even more. In fact, there have been a number of marketing campaigns targeted at convincing users that the "Green Address Bar" means that the website is completely trustworthy. And they've been pretty effective. But, as with most marketing, they didn't quite tell the truth. sure, the EV certificate may mean that the site is more trustworthy, but it's still possible that the certificate is fake.
There have been a number of well known CAs that have been compromised in recent years. Diginotar and Comodo being two of the more high profile ones. In both cases, it became possible for rogue certificates to be created for any website the attacker wanted to hijack. That certificate plus some creative DNS poisoning and the attacker suddenly looks like your bank, or google, or whatever site the attacker wants to be. And, they'll have a nice shiny green EV certificate.
So how do we fix this? Well, one way would be to use the certificate revocation system that already exists within the PKI infrastructure. If a certificate is stolen, or a false certificate is created, the CA has the ability to put the signature for that certificate into the revocation system. When a user tries to load a site with a bad certificate, a warning is displayed telling the user that the certificate is not to be trusted.
Checking revocation of a certificate takes time, and what happens if the revocation server is down? Should the browser let the user go to the site anyway? Or should it block by default? The more secure option is to block, of course, but most users won't understand what's going on. So most browser manufacturers have either disabled revocation checking completely, or they default to allowing a user to access the site when the revocation site is slow or unavailable.
Without the ability to verify if a certificate is valid or not, there can be no real trust in the security of the connection, and that's a problem. Perhaps one way to fix this problem is to disconnect the revocation process from the process of loading the webpage. If the revocation check happened in parallel to the page loading, it shouldn't interfere with the speed of the page load. Additional controls can be put into place to prevent any data from being sent to the remote site without a warning until the revocation check completes. In this manner, the revocation check can take a few seconds to complete without impeding the use of the site. And after the first page load, the revocation information is cached anyway, so subsequent page loads are unaffected.
Another option, floated by the browser builders themselves, is to have the browser vendors host the revocation information. This information is then passed on to the browsers when they're loaded. This way the revocation process can be handled outside of the CAs, handling situations such as those caused by a CA being compromised. Another idea would be to use short term certificates that expire quickly, dropping the need for revocation checks entirely.
It's unclear as to what direction the market will move with this issue. It has been over two years since the attacks on Diginotar and Comodo and the immediacy of this problem seems to have passed. At the moment, the only real fix for this is user education. But with the marketing departments for SSL vendors working to convince users of the security of SSL, this seems unlikely.
Tuesday, November 12. 2013
The annual BSides Delaware conference took place this past weekend, November 8th and 9th. BSides Delaware is a free community driven security event that takes place at the Wilmington University New Castle campus. The community is quite open, welcoming seasoned professionals, newcomers, curious individuals, and even children. There were a number of families who attended, bringing their children with them to learn and have fun.
I was fortunate enough to be able to speak at last years BSides and was part of the staff for this years event. There were two tracks for talks, many of which were recorded and are already online thanks to Adrian Crenshaw, the IronGeek. Adrian has honed his video skills and was able to have every recording online by the closing ceremonies on Saturday evening.
In all there were more than 25 talks over the course of two days covering a wide variety of topics, logging, Bitcoins, forensics, and more. While most speakers were established security professionals, there were a few new speakers striving to make a name for themselves.
This year also included a FREE wireless essentials training class. The class was taught by a team of world-class instructors including Mike Kershaw (drag0rn), author of the immensely popular Kismet wireless tool, Russell Handorf from the FBI Cyber Squad, and Rick Farina, lead developer for Pentoo. The class covered everything from wireless basics to software-defined radio hacking. An absolutely amazing class.
In addition to the talks, BSides also features not one, but two lockpick villages. Both Digital Trust as well as Toool were present. The lockpick villages were a big hit with seasoned professionals as well as the very young. It's amazing to see how adept a young child can be with a lockpick.
Hackers for Charity was present as well with a table of goodies for sale. They also held a silent (and not so silent) auction where all proceeds went to the charity. Hackers for Charity raises money to help with a variety of projects they engage in across the world. From their website :
We employ volunteer hackers and technologists through our Volunteer Network and engage their skills in short projects designed to help charities that can not afford traditional technical resources.
BSides 2013 was an amazing experience. This was my second year at the conference and it's amazing how it has grown. The dates for BSidesDE 2014 have already been announced, November 14th and 15th. Mark your calendars and make an effort to come join in the fun. It's worth it.
Saturday, October 6. 2012
I spent this past weekend in Louisville, KY attending a relatively new security conference called Derbycon. This year was the second year they held the conference and the first year I spoke there. It was amazing, to say the least.
Sunday, August 26. 2012
I listened to a news story on NPR's On The Media recently about "Cyber Warfare" and assessing it's true threat. On the one hand, it seemed like another misguided report from a clueless news media. On the other hand, though, it did make me think a bit.
Much of the talk about Cyber Warfare revolves around attacking the various SCADA systems used to control the nation's physical infrastructure. By today's standards, many of these systems are quite primitive. Many of these systems are designed for a very specific purpose, rarely upgraded to run on modern operating systems, and very rarely, if ever, designed to be secure. The state of the art in security for many of these systems is to not allow outside access to the system.
Unfortunately, if numerous reports are to be believed, a good portion of the world's infrastructure is connected to the Internet in one manner or another. The number of institutions that truly air gap their critical networks is alarmingly low. A researcher from IO Active, who provided some of the information for the aforementioned NPR article, used SHODAN to scour the Internet for SCADA systems. Why use SHODAN? Turns out, the simple act of scanning the Internet for these systems often resulted in the target systems crashing and going offline. If a simple network scan can kill one of these systems, then what hope do we have?
But, air gapping is by no means a guarantee against attacks since users of these systems may regularly switch between connected and non-connected systems and use some form of media to transfer files back and forth. There is precedence for this with the Stuxnet virus. According to reports, the Iranian nuclear facility was, in fact, air gapped. However, Stuxnet was designed to replicate onto USB drives and other media. Plug an infected USB drive into a targeted SCADA system and poof, instant infection across an air gapped system.
So what can be done here? How do we keep our infrastructure safe from attackers? Yes, even aging attackers…
Personally, I believe this comes down, again, to Defense in Depth. With the exception of not building it in the first place, I don't believe that there is a way to prevent attacks. And any determined attacker will eventually get in, given time. So the only way to defend against this is to build a layered defense grid with a full monitoring back end. Expect that attackers will make it through one or two layers before being detected. Determined attackers may make it even further. But if you build you defenses with this in mind, you will stand a better chance at detecting and repelling these attacks.
I don't believe that air gapping systems is a viable security strategy. If anything, it can result in a false sense of security for users and administrators. After all, if the system isn't connected, how can it possibly be infected? Instead, start building in security from the start and deploy your defense in monitored layers. It works.
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"Chance favors the prepared mind."