CVE-2008-5100 in .NET Framework
Summary
by MITRE
The strong name (SN) implementation in Microsoft .NET Framework 2.0.50727 relies on the digital signature Public Key Token embedded in the pathname of a DLL file instead of the digital signature of this file itself, which makes it easier for attackers to bypass Global Assembly Cache (GAC) and Code Access Security (CAS) protection mechanisms, aka MSRC ticket MSRC8566gs.
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Analysis
by VulDB Data Team • 08/03/2021
The vulnerability described in CVE-2008-5100 represents a critical flaw in the Microsoft .NET Framework 2.0 implementation that fundamentally undermines the security model designed to protect applications from malicious code execution. This weakness specifically affects the strong name implementation mechanism that is integral to the Global Assembly Cache and Code Access Security systems. The core issue lies in how the framework validates digital signatures, creating an exploitable condition that allows attackers to circumvent fundamental security controls.
The technical flaw stems from the incorrect handling of public key tokens within the strong name verification process. Instead of validating the actual digital signature embedded within the DLL file itself, the implementation relies on the public key token that is stored in the file path or metadata structure. This approach creates a significant security gap because the public key token can be manipulated or forged more easily than the actual cryptographic signature. The vulnerability affects the Global Assembly Cache mechanism which is designed to store and manage shared assemblies while maintaining their integrity through strong naming. When the system validates assemblies, it should verify the cryptographic signature against the actual file content rather than relying on path-based metadata.
This security weakness directly impacts the Code Access Security model by enabling attackers to bypass critical access controls that are supposed to prevent unauthorized code execution. The operational impact is severe as it allows malicious actors to deploy assemblies that appear legitimate within the GAC while actually containing harmful code. An attacker could create a DLL with a valid public key token but malicious payload, and the system would incorrectly accept it as trustworthy due to the flawed verification process. This vulnerability essentially undermines the entire trust model of the .NET Framework by allowing attackers to manipulate the strong name validation process to gain elevated privileges or execute arbitrary code.
The vulnerability aligns with CWE-310 and CWE-311 categories related to cryptographic weaknesses and the improper handling of cryptographic tokens. From an ATT&CK perspective, this flaw maps to techniques involving privilege escalation and persistence mechanisms, particularly T1068 (Local Privilege Escalation) and T1059 (Command and Scripting Interpreter) where attackers can leverage the compromised GAC to execute malicious code. Organizations running .NET Framework 2.0 applications are particularly vulnerable since this issue affects the core security infrastructure that protects against malicious assembly loading. The attack surface expands significantly because any application relying on GAC-based security controls becomes susceptible to this type of bypass.
Mitigation strategies should include immediate patching of affected .NET Framework versions, implementing additional verification mechanisms beyond the default strong name validation, and monitoring GAC installations for suspicious assemblies. System administrators should also consider disabling unnecessary GAC functionality and implementing strict access controls around assembly deployment processes. The recommended approach involves applying Microsoft security updates that correct the strong name validation logic and ensuring that all assemblies are properly signed with valid cryptographic signatures rather than relying on potentially manipulable public key tokens. Organizations should also implement comprehensive monitoring solutions that can detect unauthorized GAC modifications and maintain detailed audit trails of assembly installations and updates.