CVE-2018-1120 in Linux
Summary
by MITRE
A flaw was found affecting the Linux kernel before version 4.17. By mmap()ing a FUSE-backed file onto a process's memory containing command line arguments (or environment strings), an attacker can cause utilities from psutils or procps (such as ps, w) or any other program which makes a read() call to the /proc/<pid>/cmdline (or /proc/<pid>/environ) files to block indefinitely (denial of service) or for some controlled time (as a synchronization primitive for other attacks).
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Analysis
by VulDB Data Team • 12/10/2024
The vulnerability identified as CVE-2018-1120 represents a significant denial of service flaw within the Linux kernel's memory management subsystem that affects versions prior to 4.17. This weakness specifically targets the interaction between the Filesystem in Userspace (FUSE) framework and the /proc filesystem, creating a condition where malicious actors can exploit the mmap() system call to map FUSE-backed files into memory spaces containing process command line arguments or environment strings. The flaw operates through a sophisticated race condition that leverages the kernel's handling of memory mapping operations in conjunction with the /proc filesystem's interface to process information.
The technical implementation of this vulnerability exploits the kernel's memory management architecture by creating a scenario where a process attempts to map a FUSE-backed file into its address space while simultaneously accessing the /proc/<pid>/cmdline or /proc/<pid>/environ files. When a process's command line arguments or environment variables are stored in memory that is subsequently mapped via mmap() to a FUSE file, the kernel's handling of read() operations on these proc files becomes susceptible to indefinite blocking. This occurs because the FUSE subsystem's implementation creates a circular dependency where the kernel's memory management operations conflict with the proc filesystem's attempt to read process metadata, resulting in a deadlock condition that can persist indefinitely.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it provides attackers with a sophisticated synchronization primitive that can be leveraged for more complex attack vectors. Programs that rely on reading /proc/<pid>/cmdline or /proc/<pid>/environ files for process monitoring, system administration, or security auditing purposes become vulnerable to indefinite blocking, effectively rendering system monitoring tools and security utilities ineffective. This vulnerability particularly affects utilities from the psutils and procps packages, including ps, w, and other process monitoring tools that make read() calls to these sensitive kernel interfaces. The blocking behavior can be either indefinite or controlled, allowing attackers to use it as a timing mechanism for race condition attacks or other sophisticated exploitation techniques.
This vulnerability maps directly to CWE-367, which describes the Time-of-Check to Time-of-Use (TOCTOU) error condition, and aligns with ATT&CK technique T1059.003 for execution through command and scripting interpreter. The flaw represents a critical weakness in the kernel's memory management and file system interaction model, particularly in how it handles concurrent access patterns between different kernel subsystems. The vulnerability demonstrates how seemingly isolated kernel components can create dangerous interaction patterns that result in system-wide availability issues. Organizations using Linux systems with kernel versions prior to 4.17 face significant risk from this vulnerability, as it can be exploited by unprivileged users to cause system instability and denial of service conditions that affect system monitoring and security auditing capabilities. The remediation strategy involves upgrading to kernel version 4.17 or later, where the kernel developers have implemented proper locking mechanisms and memory management protocols that prevent the race condition from occurring.
The broader implications of this vulnerability highlight the complexity of modern kernel security and the challenges of ensuring proper synchronization between different subsystems. It demonstrates how kernel vulnerabilities can be exploited to create persistent denial of service conditions that are difficult to detect and mitigate, particularly in environments where system monitoring tools are essential for security operations. The vulnerability serves as a reminder of the importance of thorough testing and validation of kernel memory management operations, especially when multiple subsystems interact through shared interfaces. Security practitioners should monitor for this vulnerability in systems using older kernel versions and ensure proper patch management procedures are in place to address similar issues in the future. The flaw also underscores the need for comprehensive kernel security auditing that examines interaction patterns between different subsystems rather than focusing solely on individual component vulnerabilities.