CVE-2016-5195 in Communications
Summary
by MITRE • 01/25/2023
Race condition in mm/gup.c in the Linux kernel 2.x through 4.x before 4.8.3 allows local users to gain privileges by leveraging incorrect handling of a copy-on-write (COW) feature to write to a read-only memory mapping, as exploited in the wild in October 2016, aka "Dirty COW."
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Analysis
by VulDB Data Team • 01/29/2025
The vulnerability identified as CVE-2016-5195 represents a critical race condition flaw within the Linux kernel's memory management subsystem, specifically in the mm/gup.c file. This issue affects kernel versions ranging from 2.x through 4.x, with the vulnerability remaining unpatched until the release of kernel version 4.8.3. The flaw emerged as a significant security concern when it was actively exploited in the wild during October 2016, earning the moniker "Dirty COW" due to its ability to corrupt memory through a sophisticated privilege escalation technique. The vulnerability stems from improper handling of copy-on-write mechanisms, which are fundamental to memory management in operating systems.
The technical execution of this vulnerability exploits a race condition that occurs during memory mapping operations, particularly when dealing with read-only memory segments that should be protected from modification. When a process attempts to write to a read-only memory mapping, the kernel should normally trigger a page fault and handle the copy-on-write operation by creating a new writable page for that process. However, the race condition allows an attacker to manipulate timing windows between the initial read-only mapping check and the actual page fault handling, enabling them to write to memory regions that should remain protected. This flaw specifically targets the get_user_pages function and related memory management routines that handle user-space memory access, creating a window where memory protection mechanisms can be bypassed through carefully timed system calls.
The operational impact of this vulnerability extends far beyond simple memory corruption, as it provides local attackers with a powerful privilege escalation vector that can elevate their access level from regular user to root privileges. Attackers can leverage this vulnerability to modify critical system files, inject malicious code into running processes, or establish persistent backdoors within the system. The exploitability of this vulnerability in the wild demonstrates its practical utility for attackers, as it can be used to compromise systems without requiring network access or sophisticated attack vectors. The race condition nature of the flaw means that exploitation is highly reliable across different kernel versions and system configurations, making it particularly dangerous for system administrators to address.
Mitigation strategies for CVE-2016-5195 require immediate kernel updates to versions 4.8.3 or later, where the race condition has been properly addressed through enhanced synchronization mechanisms and improved memory management handling. System administrators should prioritize patching all affected systems, particularly those running older kernel versions where the vulnerability remains present. Additional protective measures include implementing strict access controls, monitoring for suspicious memory access patterns, and maintaining up-to-date security scanning tools that can detect exploitation attempts. The vulnerability aligns with CWE-362, which addresses race conditions in concurrent systems, and maps to ATT&CK technique T1068, which covers privilege escalation through local exploits. Organizations should also consider implementing kernel lockdown features and restricting user privileges to minimize potential damage from successful exploitation attempts.