CVE-2002-0766 in OpenBSD
Summary
by MITRE
OpenBSD 2.9 through 3.1 allows local users to cause a denial of service (resource exhaustion) and gain root privileges by filling the kernel s file descriptor table and closing file descriptors 0, 1, or 2 before executing a privileged process, which is not properly handled when OpenBSD fails to open an alternate descriptor.
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Analysis
by VulDB Data Team • 06/24/2024
This vulnerability exists in OpenBSD versions 2.9 through 3.1 and represents a sophisticated privilege escalation flaw that combines resource exhaustion with improper file descriptor handling. The vulnerability stems from a critical design flaw in how the operating system manages file descriptors during privileged process execution. When local users systematically fill the kernel's file descriptor table and subsequently close standard file descriptors zero, one, or two before executing a privileged process, the system fails to properly handle the alternate descriptor opening process. This creates a race condition where the kernel cannot adequately manage the descriptor allocation, leading to both denial of service and potential privilege escalation. The vulnerability operates at the kernel level and demonstrates a fundamental weakness in the system's resource management and error handling mechanisms.
The technical exploitation of this vulnerability requires a deep understanding of Unix-like operating system internals and process management. Attackers must first exhaust the available file descriptor table through various means, typically by opening numerous files or network connections until the system reaches its limits. Once the table is filled, the attacker must then close file descriptors zero, one, or two, which are typically stdin, stdout, and stderr respectively. This specific manipulation creates a scenario where subsequent privileged processes cannot properly establish their standard I/O streams. The root cause lies in the kernel's failure to properly handle the descriptor allocation when encountering the exhausted table condition, resulting in a cascade of failures that can be leveraged for privilege escalation. This flaw directly relates to CWE-362, which describes concurrent execution using shared resource access, and CWE-412, which addresses improper access control in privileged operations.
The operational impact of this vulnerability extends beyond simple denial of service to include complete system compromise. When successfully exploited, local users can gain root privileges, effectively providing them with unrestricted access to the entire system. This includes the ability to modify system files, create new user accounts, install malware, and bypass all security controls. The vulnerability is particularly dangerous because it requires minimal privileges to initiate the attack and can be executed without network access. The resource exhaustion component makes it difficult to detect since it can be performed silently in the background, while the privilege escalation aspect provides the attacker with persistent access to the compromised system. This vulnerability also impacts the system's availability, as the denial of service component can prevent legitimate users from accessing system resources and services.
Mitigation strategies for this vulnerability must address both the immediate exploitation vectors and the underlying kernel design flaw. The most effective approach involves updating to OpenBSD versions that have patched this vulnerability, as the original issue was resolved in subsequent releases through improved file descriptor handling and resource management. System administrators should implement strict limits on file descriptor usage through process limits and resource controls to prevent attackers from easily exhausting the table. Additionally, monitoring for unusual file descriptor patterns and implementing intrusion detection systems can help identify potential exploitation attempts. The vulnerability highlights the importance of proper error handling in kernel code and demonstrates why defensive programming practices are critical for operating system security. Organizations should also consider implementing mandatory access controls and privilege separation mechanisms to limit the impact of such vulnerabilities. This case study underscores the necessity of comprehensive security testing for kernel-level operations and the importance of following security best practices outlined in frameworks such as the ATT&CK matrix, particularly in relation to privilege escalation techniques and system resource manipulation.