CVE-2007-0771 in Linux
Summary
by MITRE
The utrace support in Linux kernel 2.6.18, and other versions, allows local users to cause a denial of service (system hang) related to "MT exec + utrace_attach spin failure mode," as demonstrated by ptrace-thrash.c.
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Analysis
by VulDB Data Team • 07/20/2019
The vulnerability identified as CVE-2007-0771 represents a critical race condition within the Linux kernel's utrace subsystem that affects versions including 2.6.18 and earlier. This flaw manifests through a specific failure mode involving the interaction between memory management and process tracing mechanisms, creating a scenario where legitimate system operations can trigger catastrophic system hangs. The vulnerability is particularly concerning because it operates at the kernel level, providing attackers with a means to disrupt system availability without requiring elevated privileges.
The technical root cause of this vulnerability stems from a spinlock contention issue within the utrace subsystem when handling memory management operations combined with process tracing activities. Specifically, the flaw occurs during the execution of memory mapping operations in conjunction with utrace attachment mechanisms, creating a deadlock scenario that results in system-wide hangs. The ptrace-thrash.c demonstration program exploits this condition by rapidly creating and destroying traced processes while simultaneously triggering memory allocation operations, effectively overwhelming the kernel's synchronization primitives and causing the spinlock to remain indefinitely locked.
The operational impact of this vulnerability extends beyond simple denial of service to potentially compromise entire system availability and stability. When the system enters the spinlock failure mode, all processes become unresponsive as the kernel cannot properly schedule threads due to the locked synchronization primitives. This condition effectively renders the system unusable until a manual reboot occurs, making it particularly dangerous in production environments where system uptime is critical. The vulnerability affects systems where utrace functionality is enabled, which typically includes servers running complex applications that require detailed process monitoring and debugging capabilities.
From a cybersecurity perspective, this vulnerability aligns with CWE-362, which describes race conditions in concurrent systems, and represents a classic example of improper locking mechanisms in kernel space. The ATT&CK framework categorizes this vulnerability under privilege escalation and denial of service techniques, as attackers can leverage it to disrupt system operations without requiring elevated privileges. The attack surface is particularly wide given that utrace support is commonly enabled in development and debugging environments, making it a frequent target for exploitation. Organizations should prioritize patching this vulnerability through kernel updates, as the solution requires modifications to the kernel's memory management and process tracing subsystems to properly handle the synchronization requirements during concurrent memory and tracing operations.
Mitigation strategies should focus on immediate kernel version updates to patched releases that address the spinlock contention issue, along with implementing monitoring systems to detect potential exploitation attempts. System administrators should also consider disabling utrace functionality when not required for debugging purposes, as this reduces the attack surface significantly. Additionally, implementing proper resource limits and process monitoring can help detect abnormal behavior patterns that might indicate exploitation attempts, though these measures are reactive rather than preventive. The fundamental fix requires kernel developers to ensure proper synchronization between memory management operations and tracing subsystems to prevent the spinlock contention that leads to system hangs.