Feeds

Stealth encoding bypasses IDS protection

Attack technique gets in under the wire

  • alert
  • submit to reddit

Build a business case: developing custom apps

Cisco's Intrusion Detection System (IDS)is not the only technology that fails to protect IIS Web servers against stealth unicode attacks.

An advisory by eEye Digital Security, reports that network and server sensors from ISS, Dragon Sensor 4.x, Snort (prior to version 1.8.1) and components of Cisco Secure IDS are affected by the issue. Symantec and Network Associates have stated that their products are not vulnerable.

Links to patches and advisories from vendors affected by the issue have been collated by Security Focus and can be found here.

Last week we reported that Cisco had to alert its customers about the problem only a day after announcing enhancements to its Secure IDS products.

In fact the non-standard method of encoding Web requests (called '%u'), which Microsoft's IIS supports but an IDS fails to decode, can allow the creation of an attack which bypasses the IDS set-ups of most vendors.

In practice, this means an attacker could modify a web-based attack, such as a "stealth" Code Red, so that requests are encoded with '%u' Unicode encoding, in order to get around IDS protection.

The obfuscation method works only because Microsoft's IIS permits a non-standard decode of html (so Apache servers, for example, are not affected).

It's worth remembering that avoiding IDS detection is only the first stage in an attack. The second stage - the compromise of the ISS Web server - is where the damage is done. Webmasters can easily stop such an attack by use of the latest security patches. But as we know, many companies are ill-disciplined in applying security patches as they come out.

IDS products, which inspect network traffic and raise alerts over suspect packets, are used for the secondary protection of IIS Web servers, so making sure they aren't fooled, still merits attention. ®

Related stories

The Cisco Intrusion Undetection System
Code Red and the Cisco Side Effect
Security software crashes Cisco kit

The essential guide to IT transformation

More from The Register

next story
Rupert Murdoch says Google is worse than the NSA
Mr Burns vs. The Chocolate Factory, round three!
Microsoft cries UNINSTALL in the wake of Blue Screens of Death™
Cache crash causes contained choloric calamity
Know what Ferguson city needs right now? It's not Anonymous doxing random people
U-turn on vow to identify killer cop after fingering wrong bloke
Germany 'accidentally' snooped on John Kerry and Hillary Clinton
Dragnet surveillance picks up EVERYTHING, USA, m'kay?
Snowden on NSA's MonsterMind TERROR: It may trigger cyberwar
Plus: Syria's internet going down? That was a US cock-up
Who needs hackers? 'Password1' opens a third of all biz doors
GPU-powered pen test yields more bad news about defences and passwords
prev story

Whitepapers

Endpoint data privacy in the cloud is easier than you think
Innovations in encryption and storage resolve issues of data privacy and key requirements for companies to look for in a solution.
Implementing global e-invoicing with guaranteed legal certainty
Explaining the role local tax compliance plays in successful supply chain management and e-business and how leading global brands are addressing this.
Top 8 considerations to enable and simplify mobility
In this whitepaper learn how to successfully add mobile capabilities simply and cost effectively.
Solving today's distributed Big Data backup challenges
Enable IT efficiency and allow a firm to access and reuse corporate information for competitive advantage, ultimately changing business outcomes.
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.