CVE-2008-3842 in .NET Framework
Summary
by MITRE
Request Validation (aka the ValidateRequest filters) in ASP.NET in Microsoft .NET Framework without the MS07-040 update does not properly detect dangerous client input, which allows remote attackers to conduct cross-site scripting (XSS) attacks, as demonstrated by a query string containing a "</" (less-than slash) sequence.
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Analysis
by VulDB Data Team • 08/02/2021
The vulnerability described in CVE-2008-3842 represents a critical weakness in Microsoft's ASP.NET framework that fundamentally undermines web application security through inadequate input validation mechanisms. This flaw exists specifically within the Request Validation feature, which is designed to prevent malicious input from being processed by web applications. The vulnerability becomes particularly dangerous when systems are running Microsoft .NET Framework versions that have not received the MS07-040 security update, leaving applications exposed to sophisticated cross-site scripting attacks that can compromise user sessions and data integrity.
The technical implementation of this vulnerability stems from the improper detection of malicious client input patterns within ASP.NET's ValidateRequest filters. Attackers can exploit this weakness by crafting specially formatted query strings containing the specific sequence "</" which represents a less-than slash combination. This particular pattern bypasses the validation checks because the system fails to properly recognize it as a potentially dangerous input sequence that could be used to inject malicious scripts into web pages. The flaw demonstrates a classic case of insufficient input sanitization where the validation logic does not adequately account for all possible encoding variations that attackers might employ to circumvent security controls.
The operational impact of this vulnerability extends far beyond simple XSS attacks, as it provides attackers with a foothold to execute more sophisticated exploitation techniques within the target environment. When successful, attackers can inject malicious scripts that execute in the context of victim browsers, potentially stealing session cookies, redirecting users to malicious sites, or performing unauthorized actions on behalf of authenticated users. This vulnerability directly maps to CWE-79, which describes Cross-Site Scripting flaws, and aligns with ATT&CK technique T1566.001 for initial access through spearphishing attachments or links. The consequences include data theft, privilege escalation, and potential compromise of entire web application ecosystems that rely on ASP.NET frameworks without proper patching.
Mitigation strategies for CVE-2008-3842 primarily focus on immediate remediation through proper security updates and comprehensive input validation implementation. Organizations must prioritize applying the MS07-040 update immediately to address the root cause of the vulnerability. Additionally, implementing robust input sanitization at multiple layers including application-level validation, web application firewalls, and proper encoding practices can provide defense-in-depth protection. Security teams should also consider implementing Content Security Policy headers, proper output encoding, and regular security assessments to identify similar validation weaknesses. The vulnerability highlights the critical importance of maintaining up-to-date security patches and demonstrates how seemingly minor validation gaps can create significant attack vectors in web applications.