CVE-2014-8173 in Linux
Summary
by MITRE
The pmd_none_or_trans_huge_or_clear_bad function in include/asm-generic/pgtable.h in the Linux kernel before 3.13 on NUMA systems does not properly determine whether a Page Middle Directory (PMD) entry is a transparent huge-table entry, which allows local users to cause a denial of service (NULL pointer dereference and system crash) or possibly have unspecified other impact via a crafted MADV_WILLNEED madvise system call that leverages the absence of a page-table lock.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 05/01/2022
The vulnerability identified as CVE-2014-8173 resides within the Linux kernel's memory management subsystem, specifically in the pmd_none_or_trans_huge_or_clear_bad function located in include/asm-generic/pgtable.h. This flaw affects Linux kernel versions prior to 3.13 and manifests exclusively on Non-Uniform Memory Access (NUMA) systems, making it particularly relevant to server and high-performance computing environments where NUMA architectures are commonly deployed. The vulnerability stems from improper handling of Page Middle Directory (PMD) entries during transparent huge page operations, creating a critical gap in kernel memory management that can be exploited by local attackers.
The technical root cause of this vulnerability lies in the function's failure to correctly identify whether a PMD entry represents a transparent huge-table entry, leading to a race condition scenario where the kernel attempts to access memory structures without proper validation. When a crafted MADV_WILLNEED madvise system call is executed, it triggers the vulnerable code path that relies on the absence of a page-table lock for optimization purposes. This design decision creates a window where the kernel can proceed with operations on PMD entries that may have been modified or cleared by concurrent operations, resulting in a NULL pointer dereference that ultimately crashes the system. The vulnerability operates at the kernel level, making it particularly dangerous as it can be exploited by any local user with access to the system.
The operational impact of CVE-2014-8173 extends beyond simple system crashes, potentially enabling local privilege escalation or more sophisticated attacks depending on the system configuration. The denial of service aspect alone can be devastating in production environments where system uptime is critical, as it can cause unexpected service interruptions and require manual system restarts. Additionally, the unspecified other impacts mentioned in the description suggest potential for more severe consequences including information disclosure or privilege escalation, though these remain unconfirmed. The vulnerability affects systems where transparent huge pages are enabled, which is common in memory-intensive applications and server environments, making it particularly concerning for enterprise deployments.
Mitigation strategies for CVE-2014-8173 primarily involve upgrading to Linux kernel version 3.13 or later, where the vulnerability has been addressed through proper PMD entry validation and improved locking mechanisms. System administrators should also consider disabling transparent huge pages if the functionality is not required for specific applications, though this may impact performance. The fix implemented in kernel 3.13 addresses the core issue by ensuring proper validation of PMD entries before attempting to access them and by implementing appropriate locking mechanisms to prevent concurrent access issues. Organizations should also monitor for similar vulnerabilities in their kernel versions and consider implementing additional security measures such as kernel lockdown features and privilege separation to limit the potential impact of such vulnerabilities. This vulnerability aligns with CWE-119 (Improper Access to Memory) and can be categorized under ATT&CK technique T1068 (Exploitation for Privilege Escalation) when exploited for more advanced attacks.