CVE-2011-0661 in Windows
Summary
by MITRE
The SMB Server service in Microsoft Windows XP SP2 and SP3, Windows Server 2003 SP2, Windows Vista SP1 and SP2, Windows Server 2008 Gold, SP2, R2, and R2 SP1, and Windows 7 Gold and SP1 does not properly validate fields in SMB requests, which allows remote attackers to execute arbitrary code via a malformed request in a (1) SMBv1 or (2) SMBv2 packet, aka "SMB Transaction Parsing Vulnerability."
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Analysis
by VulDB Data Team • 01/26/2025
The CVE-2011-0661 vulnerability represents a critical buffer overflow flaw in Microsoft Windows SMB Server services that affects multiple operating system versions including Windows XP SP2 and SP3, Windows Server 2003 SP2, Windows Vista SP1 and SP2, Windows Server 2008 Gold, SP2, R2, and R2 SP1, and Windows 7 Gold and SP1. This vulnerability specifically targets the SMB Transaction Parsing mechanism within the Server Message Block protocol implementation, creating a pathway for remote code execution attacks. The flaw resides in the improper validation of fields within SMB requests, making it particularly dangerous as it can be exploited through network-based attacks without requiring authentication. The vulnerability is classified under CWE-121 as a stack-based buffer overflow, which occurs when a program writes data beyond the boundaries of a fixed-length buffer, potentially corrupting adjacent memory locations and allowing attackers to execute malicious code with the privileges of the affected service.
The technical exploitation of this vulnerability occurs when the SMB Server service processes malformed SMBv1 or SMBv2 packets containing specially crafted transaction requests. Attackers can construct malicious SMB packets that contain oversized or improperly formatted data fields, causing the service to allocate insufficient buffer space for processing the request. When the vulnerable code attempts to copy data into these insufficiently sized buffers, it overflows into adjacent memory regions, potentially overwriting critical program execution pointers or return addresses. This buffer overflow condition can be leveraged by attackers to inject and execute arbitrary code on the target system, effectively taking control of the affected machine. The vulnerability is particularly severe because it operates at the network level and can be triggered by simply sending malicious packets to the SMB server port, typically port 445 or 139, making it an attractive target for automated exploitation tools.
The operational impact of CVE-2011-0661 is substantial as it enables attackers to achieve complete system compromise without requiring user interaction or authentication credentials. Once exploited, the vulnerability allows attackers to execute code with the highest privileges available to the SMB service, which typically runs with system-level permissions on Windows systems. This can result in unauthorized access to sensitive data, installation of backdoors, creation of persistent access mechanisms, and potential lateral movement within network environments. The vulnerability's widespread impact across multiple Windows versions makes it particularly dangerous for enterprise environments where legacy systems may not have been updated with security patches. Organizations running affected systems are vulnerable to various attack vectors including malware deployment, data exfiltration, and establishment of command and control channels, with the potential for cascading effects throughout network infrastructure.
Mitigation strategies for CVE-2011-0661 should include immediate deployment of Microsoft security patches released in March 2011, specifically addressing the SMB transaction parsing vulnerability. Organizations should disable SMBv1 protocol entirely as it is legacy and vulnerable to multiple attacks, implementing SMBv2 or SMBv3 which provide enhanced security features. Network segmentation and firewall rules should be implemented to restrict access to SMB ports from trusted sources only, while monitoring systems should be configured to detect unusual SMB traffic patterns. Additionally, implementing network intrusion detection systems can help identify exploitation attempts through signature-based detection of known malicious SMB packet structures. The vulnerability aligns with ATT&CK technique T1071.004 for application layer protocol usage and T1059.001 for command and script interpreter execution, making it a critical target for both defensive and offensive cybersecurity operations. Regular vulnerability assessments and network scanning should be conducted to identify any remaining unpatched systems within the organization's infrastructure.