CVE-2018-1094 in Linux
Summary
by MITRE
The ext4_fill_super function in fs/ext4/super.c in the Linux kernel through 4.15.15 does not always initialize the crc32c checksum driver, which allows attackers to cause a denial of service (ext4_xattr_inode_hash NULL pointer dereference and system crash) via a crafted ext4 image.
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Analysis
by VulDB Data Team • 02/26/2023
The vulnerability identified as CVE-2018-1094 represents a critical flaw in the Linux kernel's ext4 filesystem implementation that stems from improper initialization of cryptographic checksum components. This issue affects Linux kernel versions through 4.15.15 and manifests when the ext4_fill_super function fails to consistently initialize the crc32c checksum driver. The root cause lies in the incomplete initialization sequence where the filesystem driver does not properly establish the necessary checksum verification mechanisms required for extended attributes. When a maliciously crafted ext4 image is mounted, this initialization gap creates a scenario where the system attempts to access a NULL pointer during extended attribute processing, specifically within the ext4_xattr_inode_hash function. The vulnerability operates at the filesystem level and demonstrates the classic pattern of improper initialization leading to memory access violations that can be exploited to trigger system instability.
The operational impact of this vulnerability extends beyond simple denial of service to encompass potential system crashes and complete service disruption. Attackers can construct specially formatted ext4 filesystem images that, when mounted by a vulnerable system, will cause the kernel to attempt accessing uninitialized memory structures. This results in a NULL pointer dereference that ultimately leads to kernel panic and system crash. The vulnerability affects systems running kernel versions up to 4.15.15, making it particularly concerning for environments that have not yet updated to newer kernel releases. The attack vector requires physical access to the system or the ability to mount malicious filesystem images, which can occur in scenarios involving removable media, network file systems, or virtualized environments where untrusted filesystems are mounted. This vulnerability directly maps to CWE-457: Use of Uninitialized Variable, as the crc32c checksum driver remains in an uninitialized state when extended attribute processing occurs.
The exploitation of CVE-2018-1094 aligns with several techniques documented in the ATT&CK framework, particularly those related to privilege escalation and system compromise through kernel vulnerabilities. The flaw enables attackers to achieve persistent system instability by causing repeated crashes, which can be leveraged to disrupt services or potentially create conditions for further exploitation. From a security perspective, this vulnerability represents a failure in the kernel's robustness testing and initialization procedures, highlighting the importance of comprehensive validation of cryptographic components during filesystem mounting operations. The vulnerability's classification as a denial of service issue reflects the fundamental nature of the flaw, where the system's ability to properly handle filesystem operations is compromised. Organizations using Linux systems with affected kernel versions face significant risk as this vulnerability can be triggered without elevated privileges, making it particularly dangerous in multi-user environments where untrusted filesystems might be mounted by regular users.
Mitigation strategies for CVE-2018-1094 focus primarily on kernel version updates, which provide the most effective solution by incorporating proper initialization of the crc32c checksum driver. System administrators should immediately upgrade to kernel versions 4.15.16 or later where this vulnerability has been addressed through proper initialization sequences. Additionally, organizations can implement filesystem access controls that restrict mounting of untrusted filesystems, particularly in environments where removable media or network shares are frequently used. The vulnerability also underscores the importance of maintaining up-to-date security patches and implementing robust kernel hardening measures. Monitoring for system crashes or unexpected reboots that might indicate exploitation attempts can provide early warning signs of potential attacks. Organizations should also consider implementing automated patch management systems to ensure timely deployment of security updates across all system components, particularly kernel versions that handle filesystem operations. The fix implemented in subsequent kernel releases demonstrates the importance of proper resource initialization in kernel space and serves as a reminder of the critical nature of cryptographic component validation in system-level software.