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Vulnerability of TippingPoint IPS: bypassing via Unicode

Synthesis of the vulnerability 

An attacker can use urls containing Unicode characters in order to bypass the IPS.
Vulnerable systems: TippingPoint IPS.
Severity of this threat: 2/4.
Creation date: 11/07/2007.
Revision date: 12/07/2007.
Références of this weakness: BID-24855, CVE-2007-3701, VIGILANCE-VUL-6986.

Description of the vulnerability 

The UTF-8 encoding can be used to represent Unicode characters on several bytes:
 - 1 to 7 bits : 0xxxxxxx
 - 8 to 11 bits : 110xxxxx 10xxxxxx
 - 12 to 16 bits : 1110xxxx 10xxxxxx 10xxxxxx
 - 17 to 21 bits : 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
UTF-8 limits the encoding to 4 bytes and forbids usage of more bytes than necessary.

Some software do not normalize UTF-8 encodings. For example, the "." character must only be represented as 0x2E (b00101110) and not as 0xC0-0xAE (b11000000 10101110). Some web servers, such as IIS 5/5.1, accept all UTF-8 encodings.

However, TippingPoint IPS does not recognize urls encoded using long variants.

An attacker can therefore use this encoding in order to bypass the IPS.
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This computer vulnerability announce impacts software or systems such as TippingPoint IPS.

Our Vigil@nce team determined that the severity of this cybersecurity bulletin is medium.

The trust level is of type confirmed by the editor, with an origin of internet client.

A proof of concept or an attack tool is available, so your teams have to process this alert. An attacker with a specialist ability can exploit this threat alert.

Solutions for this threat 

TippingPoint IPS: corrected versions.
Versions posterior to indicated versions are corrected:
 - X-Family : version posterior to 2.5.0.6682
 - IPS devices 50, 100E, 200, 200E, 400, 1200, 2400 : version posterior to 2.5.1.6833
 - IPS devices 600E, 1200E, 2400E, 5000E : version posterior to 2.5.2.6919
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