Full-Width and Half-Width Unicode Encoding IDS/IPS/WAF Bypass Vulnerability

2007.05.18
Risk: High
Local: No
Remote: Yes
CWE: CWE-Other


CVSS Base Score: 7.5/10
Impact Subscore: 6.4/10
Exploitability Subscore: 10/10
Exploit range: Remote
Attack complexity: Low
Authentication: No required
Confidentiality impact: Partial
Integrity impact: Partial
Availability impact: Partial

GS07-01 Full-Width and Half-Width Unicode Encoding IDS/IPS/WAF Bypass Vulnerability Date & Version : 04/14/2007 - 1.0 Description : Various HTTP content scanning systems fail to properly scan full-width/half-width Unicode encoded traffic. This may allow malicious content to bypass HTTP content scanning systems. HTTP Content Scanning Systems have a pre-processor to decode various forms of HTTP encoded requests such as UTF encoding for attack signature analysis. Full-width and half-width is an encoding technique for Unicode characters. Various HTTP content scanning systems fail to properly scan full-width/half-width Unicode encoded traffic. Some Open Source or Microsoft Products such as Microsoft ISS and .NET Framework properly decode this type of encoding. But most IDS/IPS/WAF products does not properly decode full-width Unicode (%uff) encoded HTTP requests for analysis, Lowercase/Uppercase conversion and character matching. By sending HTTP traffic to a vulnerable content scanning system, an attacker may be able to bypass the content scanning system. Risk Level : High Impact : Security Bypass Systems Affected : Checkpoint Web Intelligence (Confirmed) IBM ISS Proventia Series (Confirmed) Full List of Vendors : (CERT - Vulnerability Note VU#739224) [1] Remedy : Contact your vendor for a hotfix, patch or advanced configuration. Credits : Fatih Ozavci (GamaTEAM Member) Caglar Cakici (GamaTEAM Member) It's detected using GamaSEC Exploit Framework GamaSEC Information Security Audit and Consulting Services (www.gamasec.net) Original Advisory Link : http://www.gamasec.net/english/gs07-01.html References : 1. CERT - Vulnerability Note VU#739224 http://www.kb.cert.org/vuls/id/739224 2. Unicode Home Page http://unicode.org 3. Unicode.org, Halfwidth and Fullwidth Forms http://www.unicode.org/charts/PDF/UFF00.pdf -- Best Regards Fatih Ozavci IT Security Consultant


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