CVE-2005-0452 in ASP.NET
Summary
by MITRE
Multiple cross-site scripting (XSS) vulnerabilities in Microsoft ASP.NET (.Net) 1.0 and 1.1 to SP1 allow remote attackers to inject arbitrary HTML or web script via Unicode representations for ASCII fullwidth characters that are converted to normal ASCII characters, including ">" and "<".
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Analysis
by VulDB Data Team • 08/25/2024
The vulnerability identified as CVE-2005-0452 represents a significant cross-site scripting weakness in Microsoft ASP.NET versions 1.0 through 1.1 Service Pack 1. This flaw exploits the way the framework handles Unicode fullwidth characters that are visually identical to standard ASCII characters but are processed differently during input validation and sanitization. The vulnerability specifically targets the conversion process where Unicode fullwidth characters such as U+FF1E (fullwidth greater-than sign) and U+FF1C (fullwidth less-than sign) are transformed into their ASCII counterparts during request processing. This conversion occurs in the ASP.NET pipeline before input validation occurs, creating a window where malicious actors can bypass security measures that typically filter standard ASCII characters. The issue stems from the framework's insufficient handling of character encoding normalization, particularly in how it processes Unicode fullwidth variants that are commonly used in internationalized web applications.
The technical exploitation of this vulnerability relies on the fundamental mismatch between Unicode character representation and the expected ASCII character validation logic within ASP.NET's input sanitization mechanisms. When a web application processes user input containing Unicode fullwidth characters, the ASP.NET runtime converts these characters to their ASCII equivalents during the request parsing phase. However, the security filters and validation routines that are designed to prevent XSS attacks operate on the original Unicode input before normalization occurs. This timing discrepancy allows attackers to inject malicious script code using fullwidth character equivalents of HTML tags and script delimiters that would normally be blocked by standard security measures. The vulnerability is particularly insidious because it leverages the legitimate Unicode support features of the framework while exploiting a subtle implementation gap in the security validation pipeline.
The operational impact of CVE-2005-0452 extends beyond simple script injection, potentially enabling attackers to perform session hijacking, defacement of web applications, data theft, and other malicious activities. An attacker could craft malicious input containing Unicode fullwidth characters that, when processed by an affected ASP.NET application, would bypass input validation and execute arbitrary JavaScript in the context of other users' browsers. This could lead to complete compromise of user sessions, data exfiltration, and the ability to perform actions on behalf of authenticated users. The vulnerability affects a broad range of applications built on the affected ASP.NET versions, making it particularly dangerous for organizations with extensive legacy web applications. The impact is amplified because the vulnerability operates at the framework level rather than individual application code, meaning that a single vulnerable component could affect multiple applications within the same environment.
Microsoft addressed this vulnerability through security updates that modified the input validation and sanitization processes to properly account for Unicode fullwidth character conversions before security checks are performed. Organizations should implement comprehensive input validation strategies that consider all possible character representations including Unicode variants, and deploy proper output encoding techniques to prevent script execution in web contexts. The vulnerability aligns with CWE-79 (Cross-site Scripting) and follows patterns commonly associated with ATT&CK technique T1203 (Exploitation for Client Execution) and T1566 (Phishing). System administrators should ensure that all affected ASP.NET applications are updated to the latest security patches and implement additional defensive measures such as Content Security Policy headers, proper input sanitization libraries, and regular security assessments of web applications to prevent similar vulnerabilities from being exploited in other components of the application stack.