Feeds

Denial, exposure and online security

Five top tips

Choosing a cloud hosting partner with confidence

Database keys are also often exposed. Attackers will attempt to manipulate the "uid" parameter in the URL below to access other user accounts.

http://www.example.com/banking/genReport?uid=10347343

A simple approach to solving direct reference issues is replacing them with indirect references. You can use an "access reference map" to assign integers to the authorized resources, and then use the integers in the web page instead of the direct reference.

When the indirect integer reference is returned, your code can look up the corresponding direct reference in the map. This prevents tampering with the parameter and significantly restricts the application's attack surface.

Only accept good input

There are hundreds of thousands of Unicode code points and dozens of different encodings. This creates a huge attack surface for your application.

As a first stage, your application should enforce a global set of allowed characters. Create a filter that rejects or at least sanitizes characters not allowed in your application.You can make the list of allowed characters as broad as it has to be, but you'll bound your attack surface. If you want to get fancy, you can create individual whitelists for the various parts of the HTTP request.

The global character whitelist often isn't enough, though. Your application will probably have to allow in some dangerous characters like apostrophe for example to support people with names like O'Malley, for example. Therefore, you also need to do specific validation on a field-by-field basis.

Validation is all about minimizing the attack surface of your application. An unvalidated form field can contain virtually any attack against a downstream interpreter or application. By enforcing a specific positive pattern, you dramatically reduce the attacker's freedom. Of course you shouldn't forget about using parameterized interfaces or output encoding/escaping, but checking the input is a critical first step.

Deny by default

Don't slip into thinking that as long as your web application does what it's supposed to, anything else it does is okay. Instead, think of your application as an API that you're exposing to attackers. What shows up in your user's browsers is irrelevant, since attackers can invoke any method with any parameters.

Many organizations are still trying to manage their attack surface with a negative approach - attempting to block attacks patterns. With the huge variety of ways to attack web applications, a positive approach implementing deny by default tends to be easier to manage and more cost-effective.

The best way to start is to go through all the layers and tiers of your application stack. Check all your configurations and security code for a default deny rule. Then just make sure all the holes in your attack surface are intentional.®

Jeff Williams is the founder and CEO of Aspect Security and the volunteer chair of the Open Web Application Security Project. His latest project is the Enterprise Security API, a free and open set of foundational security building blocks for developers.

Intelligent flash storage arrays

More from The Register

next story
UNIX greybeards threaten Debian fork over systemd plan
'Veteran Unix Admins' fear desktop emphasis is betraying open source
Netscape Navigator - the browser that started it all - turns 20
It was 20 years ago today, Marc Andreeesen taught the band to play
Redmond top man Satya Nadella: 'Microsoft LOVES Linux'
Open-source 'love' fairly runneth over at cloud event
Return of the Jedi – Apache reclaims web server crown
.london, .hamburg and .公司 - that's .com in Chinese - storm the web server charts
Chrome 38's new HTML tag support makes fatties FIT and SKINNIER
First browser to protect networks' bandwith using official spec
Admins! Never mind POODLE, there're NEW OpenSSL bugs to splat
Four new patches for open-source crypto libraries
prev story

Whitepapers

Forging a new future with identity relationship management
Learn about ForgeRock's next generation IRM platform and how it is designed to empower CEOS's and enterprises to engage with consumers.
Cloud and hybrid-cloud data protection for VMware
Learn how quick and easy it is to configure backups and perform restores for VMware environments.
Three 1TB solid state scorchers up for grabs
Big SSDs can be expensive but think big and think free because you could be the lucky winner of one of three 1TB Samsung SSD 840 EVO drives that we’re giving away worth over £300 apiece.
Reg Reader Research: SaaS based Email and Office Productivity Tools
Read this Reg reader report which provides advice and guidance for SMBs towards the use of SaaS based email and Office productivity tools.
Security for virtualized datacentres
Legacy security solutions are inefficient due to the architectural differences between physical and virtual environments.