CVE-2007-0042 in NET Framework
Summary
by MITRE
Interpretation conflict in ASP.NET in Microsoft .NET Framework 1.0, 1.1, and 2.0 for Windows 2000, XP, Server 2003, and Vista allows remote attackers to access configuration files and obtain sensitive information, and possibly bypass security mechanisms that try to constrain the final substring of a string, via %00 characters, related to use of %00 as a string terminator within POSIX functions but a data character within .NET strings, aka "Null Byte Termination Vulnerability."
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Analysis
by VulDB Data Team • 07/21/2019
The CVE-2007-0042 vulnerability represents a critical interpretation conflict within Microsoft's ASP.NET implementation that affects multiple versions of the .NET Framework including 1.0, 1.1, and 2.0. This flaw stems from the fundamental difference in how null bytes are handled across different system components, creating a dangerous discrepancy between POSIX string handling and .NET string processing mechanisms. The vulnerability specifically exploits the inconsistency where the null byte character %00 serves as a string terminator in POSIX functions while functioning as a regular data character within .NET string representations, creating a dangerous gap in security validation and access control.
The technical exploitation of this vulnerability occurs through the manipulation of string inputs that contain null byte characters, allowing attackers to bypass security mechanisms designed to constrain string operations. When .NET processes strings containing %00 characters, the framework's interpretation of these null terminators conflicts with the underlying operating system's handling of such characters, particularly in file path validation and configuration file access scenarios. This interpretation conflict enables remote attackers to access sensitive configuration files that should normally be protected, potentially exposing critical system information including database connection strings, encryption keys, and other security-sensitive data that would typically be restricted to authorized users only.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides attackers with the capability to bypass security mechanisms that attempt to constrain string operations and limit access to system resources. This vulnerability affects Windows 2000, XP, Server 2003, and Vista operating systems, creating widespread exposure across multiple platform versions. The security implications are particularly severe because attackers can leverage this flaw to gain unauthorized access to configuration files containing sensitive information, potentially leading to complete system compromise. The vulnerability's ability to bypass security controls that attempt to constrain final substrings of strings makes it especially dangerous in applications that rely on string validation for access control and input sanitization.
This vulnerability aligns with CWE-128, which addresses "Wrap-around Error" in string operations, and demonstrates characteristics similar to ATT&CK technique T1059.001 for command and scripting interpreter execution. The flaw represents a classic case of buffer over-read or over-write conditions that occur when different system components interpret the same data differently, creating exploitable gaps in security controls. Organizations affected by this vulnerability should implement immediate mitigations including input validation and sanitization, proper string handling procedures, and application-level restrictions on null byte character processing. The vulnerability also highlights the importance of consistent security practices across different system layers and the need for thorough testing of string handling mechanisms in security-critical applications.
Microsoft addressed this vulnerability through security updates that modified how .NET Framework handles null byte characters in string processing, ensuring consistent interpretation across different system components. However, the fundamental issue demonstrates the complexity of maintaining security consistency across heterogeneous system environments where different components may interpret identical data through different lenses. Organizations should implement comprehensive security testing that includes string manipulation scenarios, particularly focusing on character encoding and null byte handling, to prevent similar vulnerabilities from being exploited in other applications and systems. The vulnerability serves as a critical reminder of the importance of consistent security implementations across all layers of system architecture and the potential consequences of interpretation conflicts in security-critical code paths.