CVE-2017-7286 in Linux
Summary
by MITRE
The Linux kernel package 3.16.0-28 on Ubuntu 14.04 LTS mishandles a series of mmap system calls for /dev/zero with different starting addresses, with a stated impact of "allowing for a local user to possibly gain root access," aka an "inode integer overflow."
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Analysis
by VulDB Data Team • 11/28/2022
The vulnerability identified as CVE-2017-7286 represents a critical flaw in the Linux kernel's handling of memory mapping operations for the /dev/zero device file. This issue affects Ubuntu 14.04 LTS systems running kernel version 3.16.0-28 and stems from an integer overflow condition within the kernel's inode management subsystem. The vulnerability manifests when multiple mmap system calls are performed against /dev/zero with varying starting addresses, creating a scenario where the kernel's internal accounting mechanisms fail to properly handle the cumulative memory mappings. This flaw falls under the CWE-191 Integer Underflow/Overflow classification, specifically demonstrating how improper integer handling can lead to privilege escalation vulnerabilities. The ATT&CK framework categorizes this as a privilege escalation technique through kernel exploitation, as it allows a local user to potentially elevate their privileges to root level access.
The technical implementation of this vulnerability exploits the kernel's memory management subsystem where the inode reference counting mechanism becomes compromised during consecutive mmap operations. When a user performs multiple mmap calls against /dev/zero with different starting addresses, the kernel's internal integer variables that track memory mapping information overflow, causing the system to miscalculate available resources and potentially grant unauthorized access to kernel memory regions. The integer overflow occurs in the kernel's page mapping code where the cumulative effect of multiple mappings causes the reference counter to wrap around to a value that bypasses normal access controls. This particular implementation leverages the fact that the kernel does not properly validate the cumulative effect of multiple mapping operations, allowing an attacker to manipulate the memory mapping state through carefully crafted sequences of system calls.
The operational impact of CVE-2017-7286 extends beyond simple privilege escalation as it represents a fundamental weakness in the kernel's resource management and access control mechanisms. Local users who can execute processes on the affected system can exploit this vulnerability to gain root access, effectively compromising the entire system's security posture. This vulnerability is particularly dangerous because it requires no network access and can be exploited entirely from within the local environment, making it a prime target for both casual attackers and sophisticated threat actors seeking persistent access to systems. The vulnerability affects systems that are actively running kernel versions with this specific flaw, and the impact is immediate once exploited, potentially allowing attackers to establish backdoors, modify system files, or exfiltrate sensitive data.
Mitigation strategies for CVE-2017-7286 primarily focus on kernel updates and system hardening measures. The most effective approach involves applying the official kernel security patches released by Ubuntu and the Linux kernel development team, which address the integer overflow condition in the inode handling code. System administrators should prioritize updating to kernel versions that contain the fix, typically kernel versions 4.4.0-62 and later for Ubuntu 14.04 LTS, or newer kernel versions that contain the relevant patches. Additionally, implementing kernel lockdown mechanisms, disabling unnecessary device files, and monitoring for suspicious mmap operations can help reduce the attack surface. The vulnerability also highlights the importance of regular security audits and kernel version management, as this flaw was present in widely deployed kernel versions and demonstrates how seemingly minor integer handling issues can have major security implications. Organizations should also consider implementing process monitoring and anomaly detection systems that can identify unusual patterns of mmap system calls that might indicate exploitation attempts.