Post Tue May 15, 2007 9:16 pm

Critical Unicode Flaw Undercuts Firewalls, Scanners

By Lisa Vaas
May 15, 2007

Updated: US-CERT reports that 92 security products by different vendors, including Cisco, may have a serious security hole. Given these products' market share, most businesses could be affected.

The U.S. Computer Emergency Response Team is reporting a network evasion technique that uses full-width and half-width unicode characters to allow malware to evade detection by an IPS or firewall.

The vulnerability affects virtually every major firewall and intrusion prevention system available, including products from Cisco Systems. Given Cisco's major share of the market, at least for enterprise routers and VPN and firewall equipment—according to Gartner, Cisco was at the top of the heap with 66 percent of that market in 2006—that means most businesses will be affected.

The vulnerability concerns HTTP content-scanning systems that fail to properly scan full-width and half-width Unicode-encoded HTTP traffic. A remote attacker could exploit the vulnerability by sending specially crafted HTTP traffic to a vulnerable content scanning system. After sneaking malware past the firewall or IPS, the attacker can then wreak havoc on a system, scanning and attacking without being detected.

Multiple Cisco products are affected, including Cisco's IPS CSCsi58602 and its Cisco IOS with Firewall/IPS Feature Set CSCsi67763. Cisco has an advisory up. In the advisory the company states that it's not aware of any exploits of the vulnerability.

While Cisco is the only vendor to have verified that its products are vulnerable, there's a long list of vendors that haven't said whether their products are vulnerable or not.

Specifically, the US-CERT note lists 92 vendors whose security products may be vulnerable; of those, as of the afternoon of May 15, only two—Apple and Hewlett-Packard—had verified that their security software isn't vulnerable.

The list of other companies' products whose vulnerability status is unknown ranges widely, from products by 3Com and F5 Networks to the open-source Snort and just about every other well-known security product out there.

The vulnerability has been known since at least April 16 and was made public on May 14.

For original story:,1895,2130397,00.asp