CVE-2019-10125 in Linux
Summary
by MITRE
An issue was discovered in aio_poll() in fs/aio.c in the Linux kernel through 5.0.4. A file may be released by aio_poll_wake() if an expected event is triggered immediately (e.g., by the close of a pair of pipes) after the return of vfs_poll(), and this will cause a use-after-free.
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Analysis
by VulDB Data Team • 08/08/2023
The vulnerability identified as CVE-2019-10125 represents a critical use-after-free condition within the Linux kernel's asynchronous I/O subsystem. This flaw exists in the aio_poll() function located in fs/aio.c and affects Linux kernel versions through 5.0.4, making it a persistent threat across multiple kernel releases. The vulnerability stems from improper handling of file reference counting during asynchronous I/O operations, specifically when dealing with pollable file descriptors. The issue manifests when a file descriptor is closed or becomes unavailable immediately after the vfs_poll() function returns, creating a race condition that allows the kernel to attempt to access memory that has already been freed.
The technical exploitation of this vulnerability occurs through a specific sequence of operations involving asynchronous I/O polling mechanisms. When aio_poll() is invoked, it calls vfs_poll() to check for available events on file descriptors. If an event occurs immediately after vfs_poll() returns, such as when a pipe pair is closed, the aio_poll_wake() function may trigger file release operations. This timing window creates a scenario where the kernel attempts to dereference a pointer to a file structure that has already been freed, resulting in a use-after-free condition. The vulnerability is particularly dangerous because it can lead to arbitrary code execution or system crashes, as the freed memory may be reallocated and accessed by malicious actors. This type of vulnerability falls under CWE-416, which specifically addresses use-after-free conditions, and represents a classic example of improper resource management in kernel space.
The operational impact of CVE-2019-10125 extends beyond simple system instability, potentially enabling privilege escalation attacks and system compromise. Attackers can leverage this vulnerability to execute arbitrary code with kernel privileges, effectively bypassing security boundaries and gaining complete control over affected systems. The vulnerability affects any system running vulnerable Linux kernel versions and can be exploited through applications that utilize asynchronous I/O operations, particularly those involving file descriptor polling. The race condition inherent in the flaw makes it challenging to predict and prevent, as it depends on precise timing between kernel operations. From an attacker's perspective, this vulnerability aligns with ATT&CK technique T1068, which involves exploiting vulnerabilities to gain system privileges, and represents a critical weakness in the kernel's memory management subsystem.
Mitigation strategies for CVE-2019-10125 focus primarily on kernel updates and patches provided by Linux kernel maintainers. System administrators should immediately apply the latest kernel patches to address this vulnerability, as the official fix resolves the race condition by properly managing file reference counts during asynchronous I/O operations. Additionally, organizations should implement monitoring solutions to detect unusual system behavior that might indicate exploitation attempts. The vulnerability highlights the importance of kernel security hardening and proper resource management in kernel space. Security teams should also consider implementing kernel lockdown mechanisms and restricting the use of potentially vulnerable asynchronous I/O operations in production environments. Regular security assessments and kernel version audits are essential to prevent exploitation of similar vulnerabilities in the future, as this flaw demonstrates the critical need for robust memory management practices in kernel code.