CVE-2009-3676 in Windows
Summary
by MITRE
The SMB client in the kernel in Microsoft Windows Server 2008 R2 and Windows 7 allows remote SMB servers and man-in-the-middle attackers to cause a denial of service (infinite loop and system hang) via a (1) SMBv1 or (2) SMBv2 response packet that contains (a) an incorrect length value in a NetBIOS header or (b) an additional length field at the end of this response packet, aka "SMB Client Incomplete Response Vulnerability."
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Analysis
by VulDB Data Team • 09/18/2018
The SMB Client Incomplete Response Vulnerability identified as CVE-2009-3676 represents a critical denial of service flaw affecting Microsoft Windows Server 2008 R2 and Windows 7 operating systems. This vulnerability resides within the kernel-level SMB client implementation and demonstrates how malformed network responses can trigger system instability. The flaw specifically impacts both SMBv1 and SMBv2 protocols, making it particularly concerning given the widespread use of these networking protocols in enterprise environments. The vulnerability operates through a precise mechanism where specially crafted response packets can cause the affected systems to enter infinite loops, ultimately resulting in complete system hangs that require manual intervention to resolve.
The technical exploitation of this vulnerability occurs when the SMB client receives response packets containing malformed NetBIOS headers with incorrect length values or includes additional length fields at the end of response packets. This particular flaw demonstrates characteristics consistent with CWE-129, which addresses issues related to insufficient validation of length values in buffer operations. The vulnerability exploits the client's failure to properly validate incoming packet structures, leading to unpredictable behavior when processing malformed data. Attackers can leverage this weakness through remote SMB servers or man-in-the-middle positions to deliver malicious packets that trigger the problematic code paths within the kernel's SMB client implementation. The infinite loop condition arises from the client's inability to properly handle these malformed responses, causing it to continuously process the malformed data without proper termination conditions.
The operational impact of this vulnerability extends beyond simple service disruption, as it can render entire systems unusable until manual restart occurs. Organizations running affected Windows versions face significant risk of operational downtime, particularly in environments where SMB services are heavily utilized for file sharing, print services, and other network operations. The vulnerability's remote exploitability means that attackers do not require physical access or local credentials to cause system instability. From an attacker perspective, this represents a low-effort, high-impact vector that aligns with ATT&CK technique T1499.004, which covers network denial of service attacks. The vulnerability affects systems across multiple deployment scenarios including workstations, servers, and domain controllers, making it particularly dangerous in enterprise networks where SMB communication is fundamental to operations.
Mitigation strategies for this vulnerability require immediate attention through Microsoft's security updates, specifically the patches released as part of the security bulletin MS09-065. Organizations should prioritize deployment of these updates across all affected systems, particularly those that are exposed to untrusted network environments or operate in high-value target positions. Network segmentation and firewall rules can provide temporary protection by limiting SMB traffic to trusted sources, though this approach does not eliminate the underlying vulnerability. System administrators should also consider implementing network monitoring to detect unusual SMB traffic patterns that might indicate exploitation attempts. The vulnerability highlights the importance of proper input validation in kernel-level code and demonstrates why robust protocol implementations are critical for system stability. Organizations should also review their SMB configuration settings to disable unnecessary SMBv1 support where possible, as this protocol is more vulnerable to various attacks compared to SMBv2. Regular security assessments and vulnerability scanning should include checks for this specific flaw, as it represents a persistent risk that can be exploited by both automated scanning tools and targeted attackers.