Duncans Security Blog An enthusiasts musings

27Nov/160

Gaps in DevOpsSec Part 2

In my previous article, I briefly went over some of the default security testing options available in existing DevOps deployment tools. In this article, I will cover what can reasonably be included in the DevOps pipeline, and a few caveats faced by security engineers who are trying to add security testing into a fully automated deployment pipeline.

The fact that security scanning can take time is just the tip of the iceberg. What must be remembered, is that no amount of automated scanning will catch every security vulnerability. Ultimately a professional penetration tester will still need to manually perform tests of their own. The trick with automated testing therefore, is to perform enough testing to account for the "low hanging fruit", but also complete the scan in "reasonable" time. While 4-5 minutes per scan may still sound unreasonable to the automation engineers, 10 minutes or more per scan will certainly be a test of their character.

The goal here is to use the APIs of security scanning tools to provide a degree of confidence in the code being deployed to production, until such time as a penetration tester can conduct a more thorough scrutiny of application. It is up to the security engineers to review scan results, identify false positives, and assist the development teams with urgently fixing any identified vulnerabilities.

How?

There are a number of ways that we can achieve our needs, given the features that automation tooling provide. The first approach automation engineers may suggest, is to build a recipe/playbook to act as an orchestration point to trigger scans on whichever server the recipe/playbook is run from. This would work, but some crafty design decisions need to be made with respect to how to make the script generic enough to work everywhere, and the waiting and post processing of results can become tricky.

For option two we could try webhooks from the configuration manager itself. This too would work, but may require a few "hacks" to get this working well, and if you are doing multiple deployments at once, this method may be prone to a lot of confusion and ultimate failure.

Option three would be to use something like a Bag-of-holding(OWASP) to provide an abstraction layer which manages security activities. This way, the pipeline will delegate security to the orchestration service. Depending on the design of this option, you could pre-install all tools on a server or virtual machine, or simply use containers(Docker). The Bag-of-holding can cater for all scanning, polling for completion, and making sense of the results.

Now that we have some options, lets look at what we might want to do with our security tools.

Network scan

To start with, we can run a simple network scan to scan the application server itself, which would have just been built from scratch by the configuration manager. Any changes to a recipe/playbook could result in a change in configuration that can leave the application server exposed. A basic network scan by a tool like Tenable's Nessus should do the trick. Nessus has a very nice API, and with a little pre-work, a generic scan template can be set up and re-used by all deployments.

Application scan

Next up we have an application scan. This one is tricky, because this is usually done manually by clicking through the application. OWASP ZAP or Portswigger's Burp would be options here. The idea is to probe the actual application for any obvious vulnerabilities. However, both ZAP and Burp have APIs available through which a decent amount of coverage can be achieved. Be warned though, that ZAP and Burp were designed to be used manually. Their APIs are crude, but they work. Don't expect any vast improvements to these APIs, either.

This scan can really run away with time if you have not tuned it correctly. At a minimum, you would want to run a spider, an active scan, and a passive scan. There are tuning guides available for both ZAP and Burp. If you are using ZAP, stopping by the OWASP Slack channel will do you some good(they can be quite helpful). In addition, the ZAP team have put together a "baseline" scan, which should give you reasonable coverage in a short time(ZAP Baseline scan).

For bonus points, you might like to run your development teams' functional tests(done with automated testing tools such as Selenium) directly through the proxy.

Compliance scan

Lastly, we can run some scans to satisfy our governance friends. Having an application server consistently, and provably compliant, has a lot of perks. To do this, you would need to decide on what your application server needs to comply to(e.g. CIS benchmarks, NIST, COBIT, etc), and then have a battery of tests to check. Ideally, during the rebuild of the application server, the configuration manager would have configured everything for compliance. The compliance tests are just for verification. Luckily, there are plenty of existing recipes/playbooks to help with this. For example, The hardening framework, CIS Ansible playbooks for CentOS/RHEL.

...and then?

Up till this point, we have launched various scans to cover different areas of the application server. These scans will invariably run till completion, and then as it stands, nothing further will happen. We have now come across a major problem: We have run our scans, but our continuous deployment tools have carried on without the results. While the deployment can be halted to wait for scans not being run directly from the deployment tool, something else needs to happen in order to proceed.

We have three sets of scan results(still in their respective scanner databases), each with potentially different severity report formats. These severities have also been determined by a third party, and may not correspond to your organisations interpretation of risk. So now the task of retrieving the results, parsing them, and making a decision about allowing the deployment to proceed or not, needs to be made. For this, something like Etsy's 411 security alerting framework would be useful. The framework would generate alerts, and based on the alert, the deployment tool may be notified to proceed or abort the deployment(this may sound easy, but I am not currently aware of any available hook on any CD tool that has this kind of functionality, natively).

Whether the deployment proceeds or not, any potential bug should be automatically added to an API-enabled issue tracking software such as Atlassian's Jira. The security engineers can then review the issues, and either declare them as false positives, or re-assign the issue to the relevant development manager for fixing.

On that note, any false positives need to be recorded in a central repository. Ideally, you would try and filter out the known false positives from being added onto the issue tracker, to prevent the re-work of again declaring the issue as a false positive.

In closing

As you can see, there are ways to include automated security scans into a continuous delivery pipeline, but any experienced security engineer or developer will know that it wont be trivially easy. The important thing is that you work out what is best for you and your organisation. However deciding that it either can't be done, or is too difficult, will potentially expose your organisation to attack should you proceed with production deployments that have not been tested.

I hope this has been an interesting read. Feel free to share this post with your friends 🙂

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18Sep/160

Gaps in DevOpsSec Part 1

[Part 2 of this article can be found here.]

I recently did some work with a bunch of great automation engineers. My task was to assist them with adding some automation with respect to security testing. It was an awesome experience, but it left me feeling a bit worried about the continuous deployment world, as far as security is concerned.

I know what you are thinking: "But all the fancy DevOps tools provide 'security' out-the-box". This is partly true, all of the DevOps pipeline tooling I have scrutinized(all of the widely adopted ones), provided static code analysis steps in the very early stages of the deployment pipeline. Static code analysis is a fantastic start, but for the most part, that is where the line is drawn.

Continuous deployment or continuous delivery?

Continuous deployment and continuous delivery are often confused. Continuous deployment is when a development team will deploy every change straight through to production(the change will still go through a battery of automated tests, if its done right). Continuous delivery differs in that the change will be ready for deployment just as quickly, but the developers may choose not to deploy immediately(the change would usually not be left "hanging" for too long though).

It is up to the automation engineers to build a deployment pipeline such that, from code to compiling, testing and deployment; everything will be done at the click of a button, and will be in production within minutes. The engineers from some of the bigger software companies, have been known to claim up to 50 deployments every day. Smaller adopters of DevOps admire the big guys, and so they tend to start chasing metrics: "How many deployments can WE do per day?".

Taking this into account, would you be satisfied that only static code analysis has been done?

Static code analysis

Diving into the static code analysis realm should quickly raise a lot of questions from an experienced programmer. SCA tools do work, and should certainly be used. However among the results, there are usually a plethora of false positives. The truth is, SCA is extremely hard to do well. Even the best tools will have their problems, and will typically only do one, maybe two languages effectively. With the assistance of a security engineer, the developers will learn to spot what is, and what isn't a false positive, but this will take time.

Time is of short supply in DevOps. Granted that the same false positives for unchanged code will pop up(which should be catalogued and marked as "OK", for future scans), any false positives picked up on new code should be verified. A decision therefore needs to be made: "Do we deploy as-is to production, and flag the code for security to verify?, or do we halt this run, until verification has taken place?"...But...Metrics...

What else should we do?

Up till now, we have scanned the code for vulnerabilities. We trust that our SCA tool is good, and that our teams didn't make a mistake when picking out false positives. We have not, however, tested the finished application for vulnerabilities, nor have we tested the server on which it is hosted. How about compliance? Have we tested that the application and infrastructure we are about to deploy comply with our security policy?

While SCA is generally well understood and handled by deployment tools, these other testing areas are completely alien. While it is certainly possible to launch these additional tests, they bring with them some major caveats for the deployment pipeline. One of these caveats is of course, time.

As for the rest, I will cover those in Part 2.

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29Feb/160

WordPress plugin security

The WordPress framework makes it very convenient for website owners(both novice and experienced) to extend the core functionality by adding plugins. The trouble is, installing plugins could potentially increase the websites attack surface. In this post, I will discuss the reasons, and how to limit exposure.

WordPress does a good job of securing its framework(the core code), most often releasing security fixes within 24 hours of discovery. Securing the web server, and following good development practice though, is ultimately left to the website owner/maintainer. While WordPress does produce(and maintain) some plugins of their own, they are not responsible for the code of 3rd party plugins.

3rd party plugins
3rd party plugins can be made by anyone: individual, or company. While a company will typically continue to support their plugin(whether it is paid, or free), an individual may not. It is worth noting when last a plugin was updated, before installing it. If possible, it would be even more beneficial to see if the developer intends on maintaining the code(with bug fixes, or additional functionality). Security fixes are especially of concern here: if the code will not be maintained, then using the plugin will leave you indefinitely vulnerable.

Furthermore, be aware that you are essentially installing code from strangers(including companies). It would be beneficial to attempt to establish some kind of assurance that the developers are credible. Any assurance would of course be discretionary, but a little digging could be unsettling enough to look at an alternate option.

Guidelines for using plugins on WordPress
With that in mind, here are some guidelines to follow when considering installing a new plugin.

Install the minimum amount of 3rd party plugins needed. Ask yourself, "Do I really need what this plugin will give me?". The more plugins installed, the greater the chance that one of them could be used to compromise your website. I personally don't believe that most 3rd party code is intentionally vulnerable, but I certainly believe that some of it could be. There are plenty of developers with good intentions, contributing their useful plugins to the community. However good intentions do not mean the developer has taken security into consideration(or perhaps they do not know how).

Check the plugin for known vulnerabilities. Thankfully, there are online databases which keep record of known WordPress vulnerabilities. My personal favourite, is wpvulndb. Wpvulndb has a nice interface for checking not only plugins, but also themes and WordPress itself. Any plugin you are thinking of installing, should be checked against this database. In addition, all your existing plugins should be checked, and rechecked on at least a monthly basis. There some plugins that offer to check automatically against wpvulndb for you(via an API), but I have not used them(e.g. Vulnerabilities check, and Plugin security scanner. In theory, their use would be helpful.

If it's not activated, delete it. This goes for themes, too. If the plugin is not in use, then remove it from your webserver. Plugins exist as files on your webserver. If not deleted, they will remain there and could be forgotten. If a vulnerability is discovered in this unused plugin, an attacker could potentially access it directly from its location on your webserver.

Trust, but verify. As already mentioned, you should attempt to verify the credibility of the plugin developer. By this, I dont mean harassing the developer, hoping for a confession. I mean look at their previous work(does it look dodgy?), look at their activity(Recent updates? users complaining of no support?). A personal or company blog is often a good place to start, if one exists. One thing to note, however, is that just because a plugin has not been updated in a while, doesn't mean it is a problem. It may not have had any updates, because none were needed(the plugin ratings should help with this). You will never be able to fully verify a developer. As long as you are content with your analysis, thats as close as you will get.

Keep your plugins updated. As with all security guidelines, I will suggest keeping your plugins updated. This will ensure that any available fixes have always been installed. Since 80% of WordPress updates are security related, it is in your best interest to update when possible. Remember, that a security vulnerability may not just be something that allows an attacker access to your data. It could also be something that affects the performance and/or availability of your website.

 

The above guidelines will not guarantee the safety of your website, but they will go a long way toward understanding and limiting the risks associated with using WordPress plugins. Feel free to provide your comments below.

 

Please note: This article is written in the context of a WordPress implementation(specifically for private users or small companies), and not meant as general guidelines for using 3rd party code. In the case of a larger company(and for other use cases outside of WordPress), vetting the code and provider would include a more comprehensive analysis, most commonly site visits, code reviews, penetration tests etc.

 

 

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15Jul/150

Regarding WordPress security

Over the last few years, WordPress has been the subject of much abuse. First from people of questionable intent, who may or may not disclose any security holes they find, and secondly from bystanders who comment on any disclosed vulnerabilities (of which there have been many). However, there are a few important things to note when regarding WordPress security. I will be discussing these points in this blog post.

Responsibility

A question needs to be asked as to where the responsibility lies with respect to securing a WordPress website. In short, both WordPress and the website owner are responsible. WordPress is a framework for creating websites (it is not just a CMS system). As such, WordPress is responsible for delivering secure code to their customers. However, they cannot do much more than that. The site owner (who may or may not be the developer), is responsible for decisions made both during implementation, as well as post implementation. Decisions like hosting platform, plugins, SSL configuration and database configuration are all out of WordPress' control.

WordPress have consistently proven that if a vulnerability is their responsibility, it is taken care of. It then falls on the website owner to run updates. Minor updates now happen automatically, but major updates still require administrative action. Updates aside, WordPress cant be held responsible for installation of compromised plugins (which is where most breaches are coming from these days; 3rd party code). WordPress should also not be held responsible for failure to use security certificates (without which, dashboard credentials can be sniffed in plaintext). Hosting is also a website owners decision. The choice of a shared hosting package for example, introduces a great deal of risk (a server compromise on someone elses website could expose all websites on the cluster).

WordPress is the most secure and most vulnerable framework, at the same time

Thats a bold statement. But did you know that 25% of all websites on the internet, are built with WordPress? Furthermore, WordPress' market share varies between 60-65% of all CMS frameworks in use. By numbers alone, that paints a massive target on WordPress implementations. Since WordPress can also be installed by a user with no technical "know-how", a good portion of implementations will be left in their default configurations, making them vulnerable (and easy targets).

Bug fixing in software is an endless process. A study done by WordPress over a period of five years on theme, core and plugin code showed that 80% of all updates were security related. History has shown that the WordPress developers are quick to patch security vulnerabilities. The same cannot be said for other popular CMS systems, which could take weeks or even months to release a patch which WordPress had implemented within 24 hours of disclosure. The quick turn around time for security patches make WordPress a secure platform (provided the site owner runs the update).

Bottom line

No website or web application will ever be 100% secure. The only way to prevent ever getting hacked, is to unplug from the internet. The most a website owner can do, is keep their software up to date, and periodically review security measures to make sure they are sufficient to protect the required assets. But with just a few key security tweaks, your WordPress installation can be orders of magnitude securer. WordPress has an army of developers collaborating and working towards a better framework for their customers.

So its all doom and gloom then... what can you do?

This post will be the first of a series of posts I will be making, going over WordPress security and best practice. At a bare minimum, you can install a trusted security plugin (I can vouch for ithemes security, wordfence, and securi). These plugins help a great deal, I will compare them in a future post.

Feel free to leave your comments, even if its a dispute 😉

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19Apr/142

Heartbleed: my comments

It has been 11 days since the public disclosure of a major bug in OpenSSL, known as Heartbleed. I have been asked about my thoughts by a few people(both technical and non-technical), and so I find myself writing this blog post. I must mention that security disclosures occur on a weekly(if not, daily) basis, but heartbleed has been one that has stood out, even to laymen. To clear the air, there is a lot of discussion about stolen passwords. This isnt necessarily true. The passwords could potentially have been stolen, but it doesnt mean they have been(and unfortunately, there is no way to know if they have been compromised).

So what is it about? Is it important? What is being overlooked?

What is it, in a nutshell?
Heartbleed is the name that has been given to a bug which was found in OpenSSL. OpenSSL is an open source implementation of the SSL and TLS protocols, which are used for secure communications across a network. OpenSSL is also by far, the most widely used implementation of SSL/TLS in the world. If you have ever logged in to any website on the internet, there is a very good chance that OpenSSL was involved. Some of the major websites that use OpenSSL, are listed in the Heartbleed hit-list.

The bug revolves around a piece of code committed to OpenSSLs codebase in 2012, known as heartbeat. OpenSSL makes use of a process of secret exchanges in order to authenticate the client and server, in order to establish a secure connection. The heartbeat feature is used to keep existing sessions "alive", when there is no data being transmitted. Heartbeat involves an exchange of an arbitrary message from the client to the server, and the subsequent reply from the server, with the same arbitrary message. However, security researchers found that there was no bound check done on this arbitrary message. So they discovered that when receiving their arbitrary message back, they could request a bigger message in response, up to 64K in size.

This meant that the server would "bleed"(hence the name, "heartbleed") the extra bits of information that where not in the original message from heartbeat, and this additional data would come directly from the servers memory. This has been nicely summarised in a comic by XKCD. Due to the nature of heartbleed, there is unfortunately no way that the use of heartbleed could have been detected, and so it is not known if or where the exploit has been used.

What can be bled from the servers memory?
The spoils are random dumps of the next blocks of memory after the heartbeat message. So this may or may not be of use to an attacker. However, it is entirely possible that the data could consist (either in full, or in part) of sensitive information, such as; the servers private key(the holy grail), user names and passwords, credit card information, sensitive documents, confidential communications. The fact that the entire key/password etc wont necessarily be returned, is not a comfort. Because the attacker can simply keep exploiting heartbleed in order to get more data, and ideally all the pieces needed to put the puzzle together.

What I would like to see, is the capture of the random numbers which have been used to create the secret keys. With these, the attacker can generate their own copy of the private key(and perhaps infer some other sensitive details to add to the spoils).

Who is vulnerable?
Heartbeat was introduced with OpenSSL version 1.0.1, and remained unchanged up to version 1.0.1f, so anyone using these versions of OpenSSL are vulnerable. The emergency release of OpenSSL version 1.0.1g on 7th April 2014 fixed the bug, by applying bounds to the heartbeat message. There are a few web services available which you can use to test a website if it is vulnerable(the websites you use, for example). One such service can be found at filippo.io. Java haters will be fascinated to know that the Java standard edition (SE) is unaffected. Microsofts servers are also mostly unaffected, because they tend to use their own implementation of TLS(SChannel). However, other products, such as OpenVPN(which can be used on a microsoft box), do use OpenSSL.

What should you do about it?
The most obvious steps for you to take, would be to change your passwords at any website that has been affected. Indeed, just about every article on heartbleed recommends this. While this is good advice, dont rush out and do it immediately. The reason behind password changes is due to the possibility that your password has already been compromised. But if you change it before the servers OpenSSL has been updated, then your astuteness will not have paid off. If you arent sure that your websites where compromised before the disclosure of heartbleed, you can be sure that there is a much higher chance that they are now. Rather verify that the server has applied the bugfix first(either by testing it with a webservice, or by taking note of any public announcements made by the website).

If you run your own server, you should update your OpenSSL, or recompile it with the -DOPENSSL_NO_HEARTBEATS option, as well as revoking and reissuing all certificates that use SSL/TLS(with new keys, of course. Have fun...), and force client password resets.

One thing which has been bugging me about all the current media coverage to date, is that they are all server centric. I havent seen much mention at all about the possibility that the client is also at risk. Indeed, if a server has been compromised, there is nothing to stop it from using heartbleed against the client. I have found an article about the possibility of a reverse heartbleed attack, where it has been shown that although it is harder to do, the clients(IE. your own devices) are also at risk.

Should we be pointing fingers at anyone about this?
In short, no. Remember that OpenSSL is an open source project. It is the most widely used implementation of SSL/TLS in the world. Not bad for a project run by a core group of four developers, only one of which is considered to be working on it full time. And the pay is next to non-existant. On average, donations to the OpenSSL Software Foundation (OSF) are a meagre $2000 per annum. They do not have the man power to do extensive code reviews, however the larger companies that use the software, do have that capability(and should have reviewed all outsourced code fully anyway, whether the code came from a small group of developers or not).

Some parting thoughts
One question on many peoples minds, is whether or not the NSA has been exploiting heartbleed all along. They claim to have had no prior knowledge of heartbleed, but then they wouldnt admit it if they had known. With their resources and tenacity, I would be surprised if heartbleed was news to them. Other, more paranoid people are saying that since it is known that the US government has worked to weaken encryption standards, they further undermined internet security by not donating any significant amount to the OSF. I think this last is a bit of a stretch. But the real question is, was the bug introduced to the code base deliberately?

Re-issuing certificates is going to be an extremely daunting task to the Certificate Authorities. I doubt they have infrastructure capable of doing all the work in the time frame they have(IE. immediately).

The use of two factor authentication(depending on which kind of 2FA), as well as perfect forward secrecy would have greatly reduced your risk to exposure. Affected servers should be sending out emails explaining the plan of action(change of password etc), but do not trust any link you may find in any of these emails. It could be a phishing attempt(we have all received such emails many times in the past, and this is the perfect opportunity to go phishin').

Lastly, I think it falls on large companies that use OpenSSL to make an effort and donate to the OpenSSL project. The OpenSSL team have done one hell of a job, and have achieved an astounding market share. Perhaps with adequate funding, heartbleed could have been prevented.

Have you got any further questions? Feel free to leave your questions and comments on this page.

Some additional info

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12Mar/120

HTTPS security

 

HTTPS is a secure layering of the HTTP protocol used for communication over a computer network, most notably used on the internet. It achieves this security by using the SSL/TLS protocol, which is the standard as far as securing web applications go. In particular, HTTPS is used by banks, social networks, live streaming services, email, instant messaging and more. SSL/TLS extends HTTP by providing a secure tunnel through which a web browser and web server communicate. By encrypting transmissions, SSL/TLS provides confidentiality and prevents unauthorised and undetected modifications, which preserves integrity.

Authenticity is ensured with a digital certificate, which establishes a binding between a public key and an entity(Eg. address, company name, persons name, hostname etc). In HTTPS' case, the public key is used by SSL/TLS to negotiate a key between the browser and server. The certificate contains the entity with its key, and is digitally signed by a certification authority(CA).

The CA is responsible for checking that the public key and entity really belong together. The entity itself can be a certificate, so the original entity can be wrapped up in certificates signed by multiple CA's. In general, a certificate can be considered valid by a web browser if there is a chain of certificates from a CA the web browser trusts, to the certificate which is checked.

Public Key Infrastructure, in a nutshell
By default, web browsers ship with a list of CAs which they may consider trustworthy. These CAs have been added to the list by the browsers creators, once they have reviewed them. The CA is audited to see if the standards imposed by the CA are sufficient (so far as verifying key-entity relationships are concerned). It is also important that the CAs systems are secure and well tested. The audit should ideally be redone annually, to ensure that the standards are kept, and that new security developments are accomodated for. Of course, the browser vendor has an interest in keeping its list of trusted CAs up to date, or else they will expose their users to potential security risks. Ultimately, the certificate acceptance is determined by the browser if it establishes at least one chain of trust to a CA it trusts.

Public key infrastructure failures

VeriSign-Microsoft certificate
In 2001, and anonymous attacker managed to persuade VeriSign(a major CA) that he was an employee of Microsoft. He was granted several certificates(with his public key) to use as a result. VeriSigns checks in 2001 were clearly not good enough to ensure a secure infrastructure.

MD5 collisions
Cryptographic hashes of the certificate are signed instead of signing the entire certificate(for various technical reasons). In the early days, the most commonly used hash function used was the MD5 hash. Many weaknesses have been found in the MD5 hash, and its use is therefore discouraged these days(in favour of one of the SHA hash functions).

An MD5 collision occurs when two different certificates have the same hash. In this case, a signature on either certificate would also be valid for the other. This was proved in 2008 when security researchers managed to generate their own sub-CA using an MD5 collision. This sub-CA then requested a signature from a CA, and then copied the signature received into their own sub-CA certificate. This meant that they were able to operate their own CA, and issue arbitrary certificates for any hostname and email address they wanted to. Soon after this proof of concept, CAs stopped using MD5.

DigiNotar
Dutch CA, DigiNotar, had become compromised when an attacker gained access to their systems and granted a certificate for *.google.com to himself, and subsequently launched a man-in-the-middle attack on Gmail. DigiNotor was removed from all browser vendors' trusted lists, and soon afterwards DigiNotar went bankrupt. The attacker who claimed responsibility remarked that other CAs were susceptible to attack, and it is therefor only a matter of time before a similar attack happens again.

Preventative measures available
Three measures available can be implemented by the website administrator, and do not require CA involvement, nor do they need to modify certificates.

HSTS
The default assumed protocol for web browsers is HTTP. If a user types an address in their browser, the browser will send an HTTP request. This request would be redirected to HTTPS in the event that the website uses HTTPS. The problem comes in where the redirect request is not protected, and can be exploited via a man-in-the-middle attack which would suppress the HTTPS request, and return a bogus page to the user, in the hope that the user enters valuable details which can be recorded.

HSTS was designed to avoid this, by specifying that every subsequent request sent to the web server shall be done over HTTPS, and that the web browser should never use HTTP on that particular website. Although still in its infancy, HSTS is used by some high profile websites, such as paypal.

Public key pinning
Public key pinning works by the web server specifying which public keys may be used in the certificate chain for a particular website. When a browser connects to the website a second time, the public keys offered in the server certificate chain are compared to the list of allowed public keys for that website. If no certificate in the chain matches at least one allowed public key, the connection is terminated.

DANE (DNS-Based Authentication of Named Entities)
If the CA is compromised, public key pinning wont work because a first time user can be impersonated. DANE can protect even the first visit to a website. Instead of pinning a public key on the first visit, the pins are stored in the users DNS records. Instead of a chain of trust from an arbitrary CA to a certificate for your hostname, a chain of trust from the operator of the DNS root zone to the DNS records for your hostname is established. The benefit of such as system is that there are over 1000 CAs which can issue valid certificates for any host name on the internet, but there is only one authority responsible for a top level domain. DANE is also not limited to HTTPS, and may be used on any SSL/TLS connection. As with public key pinning and HSTS, DANE is still in draft stages.

Presently a combination of HSTS and public key pinning is the best solution for securing a HTTPS web server against compromise or other attacks on CAs. DANEs complexity makes it more preferable when a higher level of security is required, but presently is badly supported amongst the browsers.

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2Nov/110

Session riding

I decided to make this post about web application session riding, known more formally as cross site request forgery, following a presentation about javascript malware done at one of the ISG Durban meetings. There are many ways in which a web application can be designed insecure, and much more ways in which to exploit them.

Web application security has a lot of followers, and their respective communities. One such community is OWASP. OWASP is an open source application security project, and their website is perhaps the most beneficial to anyone looking for a source of information about web security.

Vulnerabilities like XSS or SQL injection are widely used by attackers and security professionals alike, and are the most popular methods of attack. Session riding however, although not as popular, is used just as frequently.

Why is it such a threat?

Web applications do not determine whether a logged in users action is authorised or not, instead it trusts the web users instructions and considers requests as legitimate. A valid session is all that is required by the web application to confirm the validity of an action.

So how does it work?

The web uses the HTTP protocol to deliver information to the user. Every HTTP request made to the web server from the same source is taken as unrelated to any previous or future requests. Neglecting keepalive connections, this is the way a browser interacts with the web server. It is required in some circumstances that the web server remembers the previous requests, for example, when shopping online. This activity needs to be kept track of, and kept seperate to the activities of other users. As a result, cookies were brought in by developers to do just that.

Cookies are bits of information sent by the application on the server, to the user via HTTP response headers. The browsers are designed to remember these cookies. These cookies are then sent to the web pages that have the same application.

Sessions of different users are maintained by random and unique cookie strings, known as session tokens(or session IDs). The randomness and unpredictability of the session token guarantees that the server side application knows who it is communicating with.

The trouble comes in, when a web application only evaluates the origin and validity of actions solely based on a valid session token. A clever attacker only needs a pre-made URL doing the same action as the target web application, and then produce it to the user in a recognisable form, and hope that the user is logged into the legitimate web application at the time. This URL could be sent to the user in a number of ways, including via email. The valid session token would then be obtained by the attacker, and they could get access to the web application.

Such an attack could even disable a network. Say for instance on a home ADSL router. All these devices utilise the HTTP protocol to access the device control panel. Hijacking the session token would allow the attacker access to the network infrastructure, and could lead to network failure if the attacker changes settings(or perhaps they could even change all the passwords).

As more and more devices are using such interfaces, more and more session riding becomes possible. The sky is the limit, as they say. What the attacker really needs to know, is a clever way to deliver the prepared html or javascript to their targets browser (email is but one method). Even standard html tags can be used. For example, in an <img> tag one could display an image, and link it through to the desired URL. Or the URL could be opened in an <iframe> tag. Even <script> tags may be used. Links such as these can easily be displayed in web applications such as facebook, where every visitor could potentially click on it.

But it doesnt stop there

To make things worse, when session riding, the attacks are always performed from the victims IP address. Thus, according to the web server logs, everything seems to have been done by the victim.

Enough with the doom and gloom

There are, however, some limitation with session riding. If the web application checks the referrer header, the attack will fail, because the origin of the request is usually not the same as the target. However, very few web applications perform this check, and could still be unreliable if a proxy, web filtering software or other such "man in the middle" is being used.

So what measures can be taken to prevent such an attack?

The most common advice to web application developers would be adding a random challenge string to each request. This random string is tied with the user session, and is different for every new login, which prevents the attacker from fetching a valid session token. It is also good practice to provide a lease on the lifetime of a session, such that it expires after a defined period of time.

These measures, however, require the developers to do additional work to the application. In the event that the application is already complete; the redesign costs are not favourable(and would use up too many human resources), and thus the applications remain vulnerable.

On the client side, a user should be very careful as to what links they open, especially if the link has been provided in an email. Browser plugins such as noscript for firefox will also go a long way toward detecting such attacks, especially where javascript malware is concerned.

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