CVE-2011-0999 in Linux
Summary
by MITRE
mm/huge_memory.c in the Linux kernel before 2.6.38-rc5 does not prevent creation of a transparent huge page (THP) during the existence of a temporary stack for an exec system call, which allows local users to cause a denial of service (memory consumption) or possibly have unspecified other impact via a crafted application.
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Analysis
by VulDB Data Team • 10/17/2021
The vulnerability described in CVE-2011-0999 resides within the Linux kernel's memory management subsystem, specifically in the mm/huge_memory.c file. This flaw represents a critical race condition that occurs during the execution of system calls involving temporary stack allocation. The issue manifests when the kernel attempts to create transparent huge pages while a temporary stack is still active for an exec system call, creating a scenario where memory management operations can interfere with each other during process execution. This vulnerability falls under the category of improper resource management and can be classified as a memory corruption issue with potential for denial of service conditions.
The technical implementation of this vulnerability exploits a timing window where the kernel's transparent huge page mechanism conflicts with the temporary stack allocation process during exec system calls. When a process executes an exec system call, the kernel creates a temporary stack that exists for the duration of the system call execution. During this period, if the kernel attempts to create transparent huge pages, the memory management subsystem can become unstable. The flaw occurs because the kernel does not properly synchronize or prevent huge page creation when temporary stacks are present, leading to potential memory allocation conflicts that can cause excessive memory consumption or system instability. This race condition is particularly dangerous because it can be triggered by local users through carefully crafted applications, making it an attractive target for privilege escalation or denial of service attacks.
The operational impact of this vulnerability extends beyond simple denial of service conditions to potentially enable more sophisticated attacks. Local users can leverage this vulnerability to consume excessive system memory resources, effectively causing a denial of service for other processes and potentially leading to system instability or crashes. The unspecified other impacts mentioned in the CVE description suggest that this vulnerability could potentially allow for more serious consequences including privilege escalation or arbitrary code execution, depending on how the memory corruption manifests. Attackers could craft applications that repeatedly trigger this race condition to exhaust system resources or exploit the memory management instability for more advanced exploitation techniques. This vulnerability particularly affects systems running Linux kernel versions prior to 2.6.38-rc5, making it a significant concern for organizations using older kernel versions.
Mitigation strategies for this vulnerability involve upgrading to kernel versions 2.6.38-rc5 or later where the race condition has been addressed through proper synchronization mechanisms in the memory management subsystem. System administrators should also implement monitoring for unusual memory consumption patterns that could indicate exploitation attempts. The fix implemented by the kernel developers involved adding proper checks to prevent transparent huge page creation during the temporary stack phase of exec system calls, aligning with best practices for race condition prevention in kernel code. Organizations should also consider implementing additional security measures such as limiting process memory usage through cgroups or implementing memory allocation limits to reduce the potential impact of exploitation attempts. This vulnerability demonstrates the importance of proper kernel memory management synchronization and highlights the critical need for thorough testing of memory management subsystems in operating system kernels.
This vulnerability relates to several CWE categories including CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization) and CWE-476 (NULL Pointer Dereference), while also mapping to ATT&CK techniques such as privilege escalation and denial of service through resource exhaustion. The attack surface is primarily local user access, but the potential for unspecified other impacts suggests that exploitation could lead to more serious consequences including system compromise. The vulnerability underscores the complexity of modern kernel memory management and the challenges of ensuring proper synchronization in high-performance systems where multiple memory management operations must occur concurrently without conflicts.