CVE-2005-3805 in Linux
Summary
by MITRE
A locking problem in POSIX timer cleanup handling on exit in Linux kernel 2.6.10 to 2.6.14, when running on SMP systems, allows local users to cause a denial of service (deadlock) involving process CPU timers.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 06/12/2019
The vulnerability described in CVE-2005-3805 represents a critical concurrency issue within the Linux kernel's POSIX timer implementation that specifically affects systems running kernel versions between 2.6.10 and 2.6.14 on symmetric multiprocessing architectures. This flaw manifests as a race condition during the cleanup phase of POSIX timers when processes terminate, creating a potential deadlock scenario that can bring system operations to a complete halt. The issue stems from improper handling of timer locks during the exit sequence of processes, where multiple threads attempting to clean up timer resources simultaneously can result in circular wait conditions that prevent any progress.
The technical root cause of this vulnerability lies in the kernel's timer subsystem where the cleanup routine for CPU timers does not properly manage locking mechanisms when multiple threads are involved in the termination process. Specifically, when a process exits and its POSIX timers need cleanup, the kernel's locking strategy fails to prevent simultaneous access to timer structures across different CPU cores in SMP environments. This creates a scenario where thread A holds a lock required by thread B, while thread B holds a lock required by thread A, resulting in a classic deadlock condition. The vulnerability is particularly severe because it affects the core kernel timer management code that is invoked during normal process termination, making it exploitable through legitimate system operations.
The operational impact of this vulnerability extends beyond simple denial of service as it can render entire system components unusable, particularly affecting services that rely on timely process termination and timer-based operations. In practical terms, local users can exploit this vulnerability by creating processes that utilize POSIX timers and then trigger the exit sequence in a manner that activates the race condition, leading to system-wide deadlocks that may require manual intervention or system reboot to resolve. The vulnerability's exploitation requires minimal privileges and can be executed by any local user, making it particularly dangerous in multi-user environments where privilege escalation is not required. This type of vulnerability aligns with CWE-362, which describes race conditions in concurrent systems, and maps to ATT&CK technique T1499.004 for denial of service through resource exhaustion or lock manipulation.
Mitigation strategies for this vulnerability focus primarily on kernel updates to versions that contain the appropriate fixes for the timer cleanup race condition. System administrators should prioritize upgrading to kernel versions 2.6.15 or later where the locking mechanism has been corrected to properly handle concurrent access during timer cleanup operations. Additionally, monitoring systems for unusual process termination patterns or timer-related kernel warnings can help detect exploitation attempts. While workarounds such as limiting the use of POSIX timers or implementing application-level timer management may provide temporary relief, these approaches do not address the root cause and should be considered only as interim measures. The vulnerability demonstrates the critical importance of proper locking mechanisms in kernel space, particularly in SMP environments where concurrent access patterns can create complex interaction scenarios that are difficult to predict and test thoroughly.