Feeds

Denial, exposure and online security

Five top tips

Combat fraud and increase customer satisfaction

Web applications have huge attack surfaces. Most sites have hundreds of URLs, and each function has plenty of parameters, form fields, cookies, and headers for attackers to play with.

One simple way to make your web application more secure is to minimize your attack surface. Let's look at five simple ways to do this.

Tighten up your URL space

The first step is to lock down your webserver, application server, application configuration, and code tree to be sure that you're not supporting any URLs that you didn't expect.

You should also check your application for functions, backup files, temporary files, and test code that wasn't intentionally deployed. Just because they're not linked in the user interface, doesn't mean an attacker can't find and exploit them. Also, be sure you're not supporting all file extensions - just the specific ones you expect.

Ditch those hidden fields

Hidden fields are form values that aren't displayed to the user. When the user submits a form, the hidden fields are submitted just like any other form field. Attackers can easily change hidden field values to anything they want with browser tools like TamperData or WebDeveloper. Hidden fields are frequently quite vulnerable to attack because they're often overlooked when implementing validation.

You could use normal input validation techniques to check the hidden field, but the best way to check is to do a direct comparison with the value that you just set in the web page. Of course, if you can do this, there's really no point in having the hidden fields at all, so consider just getting rid of them and reducing your attack surface.

Don't expose your privates

Most applications use parameters or form fields that reference data on the server by its name or ID. Attackers love to try to access unauthorized data by tampering with these "direct" references. For example, imagine a URL that references a file on the server:

http://www.example.com/banking/fetchReport?fn=03102008.xl

Attackers will immediately attempt to manipulate the filename to access other files on the host. If the code takes the "fn" parameter and appends it to a filepath, the attacker might try sending the following to gain access to the host's password file:

 "?fn=../../../../etc/password%00"

The %00 at the end of the URL will be decoded by the container into a null byte that terminates the string, leaving only the attackers path in the parameter. There are hundreds of attack variants, so don't try to filter out attacks.

Combat fraud and increase customer satisfaction

More from The Register

next story
Ubuntu 14.04 LTS: Great changes, but sssh don't mention the...
Why HELLO Amazon! You weren't here last time
This time it's 'Personal': new Office 365 sub covers just two devices
Redmond also brings Office into Google's back yard
Next Windows obsolescence panic is 450 days from … NOW!
The clock is ticking louder for Windows Server 2003 R2 users
Half of Twitter's 'active users' are SILENT STALKERS
Nearly 50% have NEVER tweeted a word
OpenBSD founder wants to bin buggy OpenSSL library, launches fork
One Heartbleed vuln was too many for Theo de Raadt
Got Windows 8.1 Update yet? Get ready for YET ANOTHER ONE – rumor
Leaker claims big release due this fall as Microsoft herds us into the CLOUD
Microsoft TIER SMEAR changes app prices whether devs ask or not
Some go up, some go down, Redmond goes silent
Batten down the hatches, Ubuntu 14.04 LTS due in TWO DAYS
Admins dab straining server brows in advance of Trusty Tahr's long-term support landing
Red Hat to ship RHEL 7 release candidate with a taste of container tech
Grab 'near-final' version of next Enterprise Linux next week
prev story

Whitepapers

Mobile application security study
Download this report to see the alarming realities regarding the sheer number of applications vulnerable to attack, as well as the most common and easily addressable vulnerability errors.
3 Big data security analytics techniques
Applying these Big Data security analytics techniques can help you make your business safer by detecting attacks early, before significant damage is done.
The benefits of software based PBX
Why you should break free from your proprietary PBX and how to leverage your existing server hardware.
Securing web applications made simple and scalable
In this whitepaper learn how automated security testing can provide a simple and scalable way to protect your web applications.
Combat fraud and increase customer satisfaction
Based on their experience using HP ArcSight Enterprise Security Manager for IT security operations, Finansbank moved to HP ArcSight ESM for fraud management.