CVE-2009-2526 in Windows
Summary
by MITRE
Microsoft Windows Vista Gold, SP1, and SP2 and Server 2008 Gold and SP2 do not properly validate fields in SMBv2 packets, which allows remote attackers to cause a denial of service (infinite loop and system hang) via a crafted packet to the Server service, aka "SMBv2 Infinite Loop Vulnerability."
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Analysis
by VulDB Data Team • 11/16/2025
The CVE-2009-2526 vulnerability represents a critical denial of service flaw in Microsoft Windows operating systems including Vista Gold, SP1, and SP2 as well as Server 2008 Gold and SP2. This vulnerability specifically targets the Server Message Block version 2 protocol implementation within the Windows kernel, creating a scenario where malformed SMBv2 packets can trigger system instability. The flaw manifests as an infinite loop condition within the SMBv2 processing logic, causing affected systems to become unresponsive and effectively hang. This vulnerability is particularly concerning as it affects core networking functionality and can be exploited remotely without authentication, making it a prime target for automated attacks.
The technical root cause of this vulnerability lies in insufficient input validation within the SMBv2 packet parsing mechanism. When the Server service receives a crafted SMBv2 packet containing malformed field values, the parsing routine enters an infinite loop due to improper boundary checks and validation routines. This occurs because the implementation fails to properly validate the structure and content of SMBv2 headers and data fields before processing them. The vulnerability is classified as a CWE-129 Input Validation and Man-in-the-Middle weakness, specifically related to improper validation of input boundaries. The flaw demonstrates poor defensive programming practices where the system does not adequately check for malformed data before attempting to process it, leading to the system entering an unrecoverable state.
From an operational impact perspective, this vulnerability presents a significant threat to enterprise network infrastructure as it can be exploited by remote attackers to disrupt critical services without requiring any credentials or elevated privileges. The infinite loop condition causes systems to become completely unresponsive, effectively creating a denial of service condition that can impact business operations and availability. Network administrators face the challenge of identifying and mitigating this vulnerability across their entire Windows infrastructure, particularly in environments where SMBv2 is actively used for file sharing and network communication. The vulnerability can be exploited through various attack vectors including network scanning and automated exploitation tools, making it particularly dangerous in large enterprise environments.
Organizations should implement immediate mitigations including applying the relevant Microsoft security patches that address the SMBv2 validation issues. Network segmentation and firewall rules can be configured to restrict SMBv2 traffic where possible, particularly between trusted and untrusted networks. The vulnerability aligns with several ATT&CK techniques including T1499.004 for Network Denial of Service and T1071.004 for Application Layer Protocol usage. Additionally, implementing network monitoring solutions that can detect anomalous SMBv2 packet patterns may help identify exploitation attempts. System administrators should also consider disabling SMBv2 if it is not required for business operations, as this eliminates the attack surface entirely. The vulnerability underscores the importance of proper input validation and defensive programming practices as outlined in secure coding guidelines and industry standards for preventing similar issues in future implementations.