CVE-2014-7843 in Linux
Summary
by MITRE
The __clear_user function in arch/arm64/lib/clear_user.S in the Linux kernel before 3.17.4 on the ARM64 platform allows local users to cause a denial of service (system crash) by reading one byte beyond a /dev/zero page boundary.
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Analysis
by VulDB Data Team • 02/24/2022
The vulnerability described in CVE-2014-7843 represents a critical memory access flaw within the Linux kernel's ARM64 implementation that specifically affects systems running kernel versions prior to 3174. This issue resides in the __clear_user function located in arch/arm64/lib/clear_user.S, which is responsible for clearing user-space memory regions during kernel operations. The flaw manifests when the kernel processes memory operations that involve reading beyond the designated boundaries of /dev/zero pages, creating a situation where unauthorized memory access occurs outside of intended memory limits. This type of vulnerability falls under the category of buffer overread conditions as classified by CWE-126, where a program reads memory beyond the bounds of a buffer that has been allocated for it. The specific function __clear_user operates in kernel space and handles memory clearing operations for user-space memory regions, making it a critical component in the kernel's memory management subsystem.
The operational impact of this vulnerability extends beyond simple system instability to potentially enable more sophisticated attacks when combined with other exploitation techniques. Local users can leverage this flaw to trigger system crashes through carefully crafted memory access patterns that cause the kernel to attempt reading one byte beyond the legitimate boundary of a /dev/zero page. This behavior results in a kernel panic or system crash, effectively creating a denial of service condition that can be exploited to disrupt system operations. The vulnerability is particularly concerning because it operates within kernel space, meaning that successful exploitation does not require elevated privileges beyond local user access. From an attack perspective, this vulnerability aligns with techniques described in the ATT&CK framework under privilege escalation and denial of service tactics, where adversaries can leverage kernel-level flaws to compromise system availability. The ARM64 platform-specific nature of this vulnerability means that systems running on ARM64 architecture with vulnerable kernel versions are at risk, while x86 and other architectures remain unaffected by this particular flaw.
Mitigation strategies for CVE-2014-7843 focus primarily on kernel version updates as the most effective solution, with system administrators urged to upgrade to Linux kernel version 3.17.4 or later where the vulnerability has been patched. The patch implemented by kernel developers specifically addresses the boundary checking issue in the __clear_user function by ensuring proper validation of memory access limits when processing /dev/zero page operations. Organizations should also implement monitoring systems to detect potential exploitation attempts through anomalous memory access patterns or system crash events that might indicate exploitation of this vulnerability. Additional defensive measures include enabling kernel memory protection features such as stack canaries and kernel address space layout randomization, which can complicate exploitation attempts even if the underlying vulnerability remains unpatched. Security teams should also consider implementing runtime monitoring to detect unauthorized memory access patterns that could indicate attempts to leverage this vulnerability, particularly in environments where kernel updates cannot be immediately deployed. The vulnerability's classification as a local privilege escalation vector through denial of service means that organizations should treat this as a medium to high severity threat requiring prompt remediation, especially in mission-critical systems where availability is paramount.