CVE-2002-1256 in Windows
Summary
by MITRE
The SMB signing capability in the Server Message Block (SMB) protocol in Microsoft Windows 2000 and Windows XP allows attackers to disable the digital signing settings in an SMB session to force the data to be sent unsigned, then inject data into the session without detection, e.g. by modifying group policy information sent from a domain controller.
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Analysis
by VulDB Data Team • 09/06/2025
The vulnerability described in CVE-2002-1256 represents a critical security flaw in the Server Message Block protocol implementation within Microsoft Windows 2000 and Windows XP operating systems. This issue specifically targets the SMB signing mechanism that was designed to ensure data integrity and authentication between clients and servers. The vulnerability allows malicious actors to manipulate the SMB session negotiation process and disable digital signatures, effectively undermining the security controls that were intended to protect against man-in-the-middle attacks and data tampering. This weakness exists at the protocol level where the system should enforce mandatory signing but instead permits attackers to force unsigned communication.
The technical flaw manifests when an attacker can successfully negotiate an SMB session with a target system and subsequently disable the digital signing requirements that would normally validate the authenticity and integrity of transmitted data. This occurs through manipulation of the SMB protocol handshake process where the attacker can force the session to operate in an unsigned mode. Once the session is operating without digital signatures, the attacker can inject malicious data into the communication stream without detection. The protocol's design flaw allows this downgrade attack to succeed, bypassing the security mechanisms that should prevent unauthorized modifications to session data. This vulnerability specifically impacts the authentication and integrity protection mechanisms that are fundamental to SMB security.
The operational impact of this vulnerability is severe and far-reaching within enterprise environments that rely on Windows domain controllers and SMB-based file sharing. Attackers can leverage this weakness to modify critical group policy information transmitted from domain controllers, potentially compromising entire networks through domain-wide policy changes. The ability to inject data undetected means that attackers can modify user permissions, security settings, and other configuration data that flows through SMB sessions. This creates a persistent threat vector where attackers can establish backdoors, modify access controls, or disrupt normal network operations without leaving detectable traces. The vulnerability essentially allows attackers to gain unauthorized control over network security policies and user access rights, making it particularly dangerous in domain environments.
Mitigation strategies for this vulnerability involve implementing proper SMB signing enforcement at the network level and ensuring that systems are configured to require digital signatures for all SMB communications. Organizations should disable SMBv1 support where possible and implement network segmentation to limit the impact of potential attacks. The recommended approach includes configuring systems to enforce SMB signing through group policy settings and monitoring for unusual SMB session behavior. Security administrators should also implement network intrusion detection systems that can identify signature downgrade attempts and anomalous SMB traffic patterns. Additionally, keeping systems updated with the latest security patches and implementing proper network monitoring can help detect and prevent exploitation of this vulnerability. This issue aligns with CWE-310 and relates to ATT&CK techniques involving credential access and privilege escalation through protocol manipulation and session hijacking.