CVE-2005-3271 in Linux
Summary
by MITRE
Exec in Linux kernel 2.6 does not properly clear posix-timers in multi-threaded environments, which results in a resource leak and could allow a large number of multiple local users to cause a denial of service by using more posix-timers than specified by the quota for a single user.
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Analysis
by VulDB Data Team • 06/12/2019
The vulnerability described in CVE-2005-3271 represents a critical resource management flaw within the Linux kernel's implementation of posix-timers. This issue specifically affects the exec system call execution in kernel versions 2.6 and earlier, where the kernel fails to properly clean up timer resources when processes are replaced through exec operations. The flaw manifests in multi-threaded environments where multiple threads may be associated with posix-timers, creating a scenario where timer resources are not adequately released during process transitions. This improper resource handling creates a condition where timer objects persist in memory even after their associated processes have been replaced, leading to a gradual accumulation of unreleased timer resources over time.
The technical implementation of this vulnerability stems from the kernel's posix-timer subsystem not correctly managing the cleanup of timer structures during exec calls. When a process executes a new program using exec, the kernel should release all posix-timers associated with the original process. However, due to a flaw in the resource cleanup logic, certain timer objects remain allocated in the kernel's memory space. This behavior violates the fundamental principle of proper resource management where all allocated resources must be freed upon process termination or replacement. The issue is particularly pronounced in multi-threaded applications where each thread may maintain its own timer references, compounding the resource leak effect. The vulnerability is classified under CWE-404 as an improper resource release or cleanup, specifically involving timer resources within the kernel's process management subsystem.
The operational impact of this vulnerability creates significant security and stability concerns for systems running affected kernel versions. Local users can exploit this weakness by creating multiple processes that utilize posix-timers, then executing exec calls to replace those processes while allowing the timer resources to accumulate. This exploitation technique can be performed by multiple concurrent users, each contributing to the resource exhaustion. The cumulative effect results in a denial of service condition where the system's timer quota is exhausted, preventing legitimate processes from creating new posix-timers. This resource leak ultimately leads to system instability and can render the system unresponsive to new timer requests, effectively creating a denial of service scenario that affects system availability and user access to computing resources. The vulnerability directly impacts the system's ability to maintain proper process isolation and resource allocation, which are fundamental requirements for maintaining system integrity and security.
Mitigation strategies for CVE-2005-3271 require immediate kernel updates to versions that contain the proper resource cleanup logic for posix-timers during exec operations. System administrators should prioritize patching affected systems to prevent exploitation by malicious users who might attempt to consume system resources through timer-based denial of service attacks. The implementation of system limits and quotas for timer resources can serve as an additional protective measure, although this approach does not address the root cause of the vulnerability. Monitoring systems should be configured to detect unusual patterns of timer resource consumption, as this could indicate exploitation attempts. The vulnerability demonstrates the importance of proper resource management in kernel space and highlights the need for comprehensive testing of system calls, particularly those involving process transitions and resource cleanup operations. Organizations should also consider implementing process monitoring and resource allocation controls to limit the impact of such vulnerabilities and maintain system stability even when exploited. This vulnerability serves as a reminder of the critical importance of proper resource management in operating system kernels and the potential for seemingly minor implementation flaws to create significant security and availability impacts.