CVE-2017-18344 in Linux
Summary
by MITRE
The timer_create syscall implementation in kernel/time/posix-timers.c in the Linux kernel before 4.14.8 doesn't properly validate the sigevent->sigev_notify field, which leads to out-of-bounds access in the show_timer function (called when /proc/$PID/timers is read). This allows userspace applications to read arbitrary kernel memory (on a kernel built with CONFIG_POSIX_TIMERS and CONFIG_CHECKPOINT_RESTORE).
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Analysis
by VulDB Data Team • 12/27/2024
The vulnerability identified as CVE-2017-18344 represents a critical kernel-level flaw in the Linux operating system that stems from inadequate input validation within the timer_create system call implementation. This issue specifically affects the kernel/time/posix-timers.c file and exists in Linux kernel versions prior to 4.14.8, creating a persistent security risk that has been classified under CWE-125 as an out-of-bounds read vulnerability. The flaw manifests when the kernel fails to properly validate the sigevent->sigev_notify field, which is a crucial parameter in the POSIX timer notification mechanism that governs how timer expiration events are delivered to user-space processes.
The technical exploitation of this vulnerability occurs through a carefully crafted sequence of system calls that manipulate the timer notification parameters to trigger an out-of-bounds memory access within the show_timer function. This function is invoked when processes attempt to read from the /proc/$PID/timers virtual file system entry, which provides detailed information about timer objects associated with a specific process. When malicious user-space applications construct timer objects with malformed notification parameters, they can cause the kernel to traverse memory beyond the intended boundaries, resulting in the exposure of sensitive kernel memory contents to unprivileged userspace processes. This vulnerability operates at the intersection of privilege escalation and information disclosure, as it allows attackers to extract kernel memory that may contain sensitive data such as cryptographic keys, credentials, or other confidential information.
The operational impact of CVE-2017-18344 extends beyond simple information disclosure, as it fundamentally undermines the kernel's memory protection mechanisms and can potentially enable more sophisticated attacks. Attackers can leverage this vulnerability to perform reconnaissance activities by reading kernel memory contents, which may reveal memory layout information, kernel data structures, or other sensitive operational details that could be used to craft more targeted exploits. The vulnerability is particularly concerning because it requires minimal privileges to exploit, as it only needs access to create timers within the user-space environment. From an ATT&CK framework perspective, this vulnerability maps to T1059.001 (Command and Scripting Interpreter: PowerShell) and T1068 (Exploitation for Privilege Escalation) categories, as it provides a pathway for privilege escalation through information gathering and memory disclosure. The vulnerability also aligns with T1547.001 (Registry Run Keys / Startup Folder) in scenarios where attackers might use the disclosed kernel memory to identify running processes or services that could be targeted for further compromise.
Mitigation strategies for this vulnerability center around immediate kernel updates to versions 4.14.8 or later, which contain the necessary patches that properly validate the sigevent->sigev_notify field and prevent the out-of-bounds memory access. System administrators should also implement monitoring solutions to detect unusual patterns in timer creation activities or access to /proc/$PID/timers entries, as these activities may indicate exploitation attempts. Additional defensive measures include hardening kernel configurations by disabling unnecessary kernel features such as CONFIG_CHECKPOINT_RESTORE when not required, and implementing proper access controls on system resources that might be leveraged in similar attacks. The vulnerability highlights the importance of rigorous input validation in kernel space and serves as a reminder of the critical nature of maintaining up-to-date kernel versions to protect against known vulnerabilities that can be exploited to undermine system security and integrity.