CVE-2018-10876 in Android
Summary
by MITRE
A flaw was found in Linux kernel in the ext4 filesystem code. A use-after-free is possible in ext4_ext_remove_space() function when mounting and operating a crafted ext4 image.
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Analysis
by VulDB Data Team • 07/04/2023
The vulnerability identified as CVE-2018-10876 represents a critical use-after-free flaw within the linux kernel's ext4 filesystem implementation that poses significant security risks to affected systems. This issue resides in the ext4_ext_remove_space() function which handles extent removal operations during filesystem manipulation. The vulnerability manifests when a maliciously crafted ext4 image is mounted and actively operated upon, creating conditions where freed memory locations can be accessed beyond their intended lifecycle. Such a scenario enables attackers to potentially execute arbitrary code with kernel privileges, effectively compromising the entire system's security posture.
The technical nature of this flaw aligns with CWE-416, which specifically addresses use-after-free vulnerabilities where memory is accessed after it has been freed. The vulnerability occurs during the ext4 filesystem's operation when the kernel attempts to remove space from file extents while simultaneously managing memory allocation and deallocation processes. When an attacker constructs a malicious ext4 image with carefully crafted extent structures, the kernel's ext4_ext_remove_space() function processes these structures in a manner that leads to memory corruption. The freed memory locations become accessible to subsequent operations, creating opportunities for exploitation through controlled data placement and execution flow manipulation.
The operational impact of this vulnerability extends far beyond simple privilege escalation, as it represents a kernel-level exploit that can be leveraged across multiple attack vectors. Attackers can mount crafted ext4 images through various means including removable storage devices, network file systems, or even through malicious downloads that get mounted automatically by the system. Once exploited, the vulnerability allows for complete system compromise including potential privilege escalation to root level access, arbitrary code execution, and denial of service conditions that can persist across system reboots. The vulnerability affects all linux kernel versions where the ext4 filesystem is implemented, making it particularly concerning for widespread deployment scenarios.
Mitigation strategies for CVE-2018-10876 should prioritize immediate kernel updates from trusted sources to address the underlying memory management flaw in ext4 filesystem operations. System administrators should implement strict monitoring of filesystem mounting operations and consider disabling automatic mounting of external storage devices where possible. The ATT&CK framework categorizes this vulnerability under privilege escalation techniques, specifically targeting kernel-level exploits that leverage memory corruption vulnerabilities. Additional defensive measures include implementing kernel module signing requirements, enabling security modules like SELinux or AppArmor, and conducting regular vulnerability assessments of filesystem operations. Organizations should also consider network segmentation to limit the impact of potential exploitation and maintain comprehensive system monitoring to detect unauthorized filesystem mounting activities. The vulnerability demonstrates the critical importance of proper memory management in kernel space operations and highlights the need for rigorous code review processes to prevent similar issues in filesystem implementations.