CVE-2011-0654 in Windows
Summary
by MITRE
Integer underflow in the BowserWriteErrorLogEntry function in the Common Internet File System (CIFS) browser service in Mrxsmb.sys or bowser.sys in Active Directory 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 allows remote attackers to execute arbitrary code or cause a denial of service (system crash) via a malformed BROWSER ELECTION message, leading to a heap-based buffer overflow, aka "Browser Pool Corruption Vulnerability." NOTE: some of these details are obtained from third party information.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 01/06/2025
The CVE-2011-0654 vulnerability represents a critical integer underflow flaw within the CIFS browser service implementation in Microsoft Windows operating systems. This vulnerability exists in the BowserWriteErrorLogEntry function located in the Mrxsmb.sys or bowser.sys kernel drivers that handle Active Directory browsing operations. The flaw specifically manifests when processing malformed BROWSER ELECTION messages, which are part of the NetBIOS browsing protocol used for network discovery and service enumeration. The vulnerability affects a wide range of Microsoft Windows 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, as well as Windows 7 Gold and SP1, making it particularly concerning due to its broad impact surface.
The technical exploitation of this vulnerability stems from an integer underflow condition that occurs during buffer size calculations within the BowserWriteErrorLogEntry function. When a maliciously crafted BROWSER ELECTION message is received, the integer underflow causes incorrect buffer size calculations that result in heap-based buffer overflow conditions. This occurs because the vulnerability involves improper validation of message lengths and offset calculations in the browser service implementation. The flaw is categorized as a heap-based buffer overflow under CWE-121, which represents a classic memory corruption vulnerability where insufficient bounds checking allows attackers to overwrite adjacent memory regions. The integer underflow specifically maps to CWE-191, which describes the condition where an integer underflow occurs when a signed integer is decremented below its minimum representable value, leading to unexpected behavior in subsequent operations.
The operational impact of this vulnerability extends beyond simple denial of service to encompass full remote code execution capabilities. Attackers can leverage this vulnerability to execute arbitrary code with kernel-level privileges, effectively compromising the entire system. The heap corruption that occurs during exploitation allows for memory layout manipulation that can be used to overwrite critical system structures, function pointers, or return addresses. This makes the vulnerability particularly dangerous as it can be used to escalate privileges, install backdoors, or establish persistent access to affected systems. The vulnerability's classification as a remote code execution flaw aligns with ATT&CK technique T1059.007 for command and scripting interpreter, where adversaries can execute malicious code through compromised services. Additionally, the denial of service component maps to ATT&CK technique T1499.004 for network denial of service, where attackers can disrupt services by causing system crashes.
Mitigation strategies for CVE-2011-0654 primarily focus on immediate patch deployment through Microsoft's security updates, which address the underlying integer underflow condition in the browser service implementation. System administrators should prioritize patching affected systems, particularly those running older Windows versions that remain vulnerable. Network segmentation and firewall rules can help limit exposure by blocking unnecessary traffic on ports associated with the NetBIOS browsing protocol, typically UDP ports 137 and 138. Implementing network monitoring solutions that can detect malformed BROWSER ELECTION messages provides additional defense-in-depth measures. The vulnerability also highlights the importance of maintaining up-to-date security patches and following Microsoft's recommended security practices. Organizations should conduct regular vulnerability assessments to identify systems running outdated versions of Windows that may be susceptible to similar issues in the browser service implementation. Proper input validation and bounds checking in kernel-level services should be enforced through code reviews and security testing to prevent similar integer underflow conditions from occurring in future implementations.