CVE-2011-0719 in Samba
Summary
by MITRE
Samba 3.x before 3.3.15, 3.4.x before 3.4.12, and 3.5.x before 3.5.7 does not perform range checks for file descriptors before use of the FD_SET macro, which allows remote attackers to cause a denial of service (stack memory corruption, and infinite loop or daemon crash) by opening a large number of files, related to (1) Winbind or (2) smbd.
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Analysis
by VulDB Data Team • 10/18/2021
The vulnerability described in CVE-2011-0719 represents a critical flaw in the Samba file sharing implementation that affects multiple versions of the Samba 3.x series. This issue stems from insufficient validation of file descriptor ranges before the execution of the FD_SET macro, creating a scenario where remote attackers can exploit the system through carefully crafted file operations. The vulnerability specifically impacts both the Winbind service and the smbd daemon, which are fundamental components of Samba's functionality for Windows interoperability and file sharing. The flaw exists at the kernel level of Samba's network handling mechanisms, where the system fails to properly validate the boundaries of file descriptor numbers before attempting to set bits in the file descriptor set structure.
The technical exploitation of this vulnerability occurs when an attacker opens an excessive number of files simultaneously, causing the FD_SET macro to operate on invalid file descriptor ranges. This improper range checking leads to stack memory corruption as the system attempts to manipulate file descriptor bits beyond their allocated boundaries. The FD_SET macro, which is part of the standard socket programming interface, expects file descriptors to fall within specific ranges defined by the system's file descriptor limits. When these boundaries are exceeded or improperly validated, the memory layout becomes corrupted, potentially leading to unpredictable behavior including infinite loops, daemon crashes, or complete system instability. This type of vulnerability falls under the CWE-129 category of Improper Validation of Array Index, specifically manifesting as an unchecked array index in the file descriptor handling code.
The operational impact of CVE-2011-0719 extends beyond simple denial of service conditions, as it can severely compromise the availability and stability of network file sharing services. When the smbd daemon or Winbind service becomes unstable due to this vulnerability, it can result in complete service outages for organizations relying on Samba for file sharing, user authentication, or Windows domain integration. The infinite loop conditions created by the corrupted file descriptor handling can consume excessive system resources, leading to performance degradation or complete system hangs. Organizations using Samba in production environments face significant risk as attackers can easily exploit this vulnerability without requiring elevated privileges, making it particularly dangerous in multi-user or public network environments. The vulnerability also aligns with ATT&CK technique T1499.004 for Network Denial of Service, where adversaries leverage system weaknesses to disrupt network services through resource exhaustion.
Mitigation strategies for this vulnerability require immediate patching of affected Samba versions to the recommended secure releases, specifically versions 3.3.15, 3.4.12, and 3.5.7 respectively. System administrators should implement network segmentation and access controls to limit exposure of Samba services to untrusted networks, while also monitoring for unusual file descriptor usage patterns that might indicate exploitation attempts. The vulnerability demonstrates the critical importance of proper input validation and boundary checking in system-level programming, particularly for components handling network connections and file operations. Organizations should also consider implementing intrusion detection systems capable of identifying abnormal file descriptor behavior and establish regular security assessments to identify similar validation flaws in other network services. This vulnerability underscores the necessity of adhering to secure coding practices as outlined in the CERT Secure Coding Standards, specifically addressing issues related to array bounds checking and resource management in network service implementations.