CVE-2018-1093 in Linux
Summary
by MITRE
The ext4_valid_block_bitmap function in fs/ext4/balloc.c in the Linux kernel through 4.15.15 allows attackers to cause a denial of service (out-of-bounds read and system crash) via a crafted ext4 image because balloc.c and ialloc.c do not validate bitmap block numbers.
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Analysis
by VulDB Data Team • 09/14/2025
The vulnerability identified as CVE-2018-1093 represents a critical flaw in the Linux kernel's ext4 filesystem implementation that enables remote attackers to trigger system crashes and denial of service conditions. This issue resides within the ext4_valid_block_bitmap function located in the fs/ext4/balloc.c file, affecting all Linux kernel versions up to and including 4.15.15. The vulnerability stems from insufficient validation mechanisms that fail to properly verify bitmap block numbers during filesystem operations, creating a pathway for maliciously crafted ext4 image files to exploit the kernel's memory management subsystem.
The technical root cause of this vulnerability can be classified under CWE-125, which describes out-of-bounds read conditions, and CWE-129, which addresses insufficient input validation. The flaw occurs when the balloc.c and ialloc.c modules process bitmap block numbers without adequate validation checks, allowing attackers to supply invalid block references that exceed the allocated memory boundaries. When the kernel attempts to access these invalid memory locations during filesystem operations, it results in kernel memory corruption and subsequent system crashes. The vulnerability operates at the kernel level, making it particularly dangerous as it can be exploited through filesystem image manipulation without requiring special privileges or user interaction.
The operational impact of CVE-2018-1093 extends beyond simple denial of service, as it can lead to complete system instability and potential data loss. Attackers can craft malicious ext4 image files that, when mounted or processed by vulnerable systems, will trigger the out-of-bounds read conditions causing kernel panics and system crashes. This vulnerability affects systems that utilize ext4 filesystems and are exposed to untrusted filesystem images, including virtualization environments, cloud computing platforms, and systems that process external storage media. The attack vector is particularly concerning in environments where users can upload or import filesystem images, as it allows for remote exploitation without requiring local access or elevated privileges.
From an adversarial perspective, this vulnerability aligns with ATT&CK technique T1059.007 for kernel-mode rootkits and T1499.004 for network denial of service attacks. The exploitation process involves creating a specially crafted ext4 image that contains invalid block number references, which when processed by the vulnerable kernel components triggers the memory corruption. Organizations should implement immediate mitigation strategies including kernel updates to versions 4.15.16 or later where the vulnerability has been patched, filesystem validation procedures for untrusted images, and monitoring for unusual system crashes or kernel oops messages. Additionally, system administrators should consider implementing filesystem access controls and limiting the ability of untrusted users to mount or process external storage media to reduce the attack surface. The vulnerability highlights the importance of robust input validation in kernel space operations and demonstrates how seemingly minor validation gaps can result in catastrophic system failures.