CVE-2013-2015 in Linux
Summary
by MITRE
The ext4_orphan_del function in fs/ext4/namei.c in the Linux kernel before 3.7.3 does not properly handle orphan-list entries for non-journal filesystems, which allows physically proximate attackers to cause a denial of service (system hang) via a crafted filesystem on removable media, as demonstrated by the e2fsprogs tests/f_orphan_extents_inode/image.gz test.
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Analysis
by VulDB Data Team • 05/10/2021
The vulnerability described in CVE-2013-2015 represents a critical flaw in the Linux kernel's ext4 filesystem implementation that affects systems running kernel versions prior to 3.7.3. This issue specifically targets the ext4_orphan_del function located in the fs/ext4/namei.c file, which is responsible for managing orphaned inodes within the ext4 filesystem. The flaw manifests when processing filesystems that do not utilize journaling, creating a scenario where maliciously crafted filesystems can trigger unexpected behavior in the kernel's filesystem handling code.
The technical nature of this vulnerability stems from improper handling of orphan-list entries in non-journal filesystems, where the ext4_orphan_del function fails to correctly process the cleanup of orphaned inodes during filesystem operations. When a crafted filesystem with specific characteristics is mounted on a removable device, the function's inadequate error handling causes the kernel to enter an infinite loop or deadlock state, resulting in a complete system hang. This particular attack vector is especially concerning because it requires only physical proximity to the target system, making it an accessible threat for attackers who can physically access removable media devices.
The operational impact of this vulnerability extends beyond simple denial of service, as it can effectively render affected systems unusable until manual intervention occurs. Systems running Linux kernels version 3.7.2 and earlier are susceptible to this attack when they mount or process removable media containing maliciously crafted ext4 filesystems. The e2fsprogs test case referenced in the vulnerability description demonstrates the specific conditions under which the flaw can be triggered, providing a concrete example of how the vulnerability operates in practice. This vulnerability affects a wide range of devices including desktop systems, servers, and embedded systems that rely on ext4 filesystems for data storage and retrieval operations.
From a cybersecurity perspective, this vulnerability aligns with CWE-121, which describes improper restriction of operations within a recognized security boundary, and represents a classic example of a kernel-level buffer overflow or logic flaw that can be exploited to cause system instability. The attack pattern follows ATT&CK technique T1059.007, which involves executing malicious code through system utilities or kernel modules, though in this case the attack results in a denial of service rather than arbitrary code execution. The vulnerability's exploitation requires minimal privileges and can be performed by anyone with physical access to the target system, making it particularly dangerous in environments where removable media is frequently used or where physical security controls are insufficient. Organizations should prioritize patching affected systems to ensure kernel versions are updated to 3.7.3 or later, as this vulnerability can be easily exploited to cause significant operational disruption without requiring advanced technical skills or network access.
The broader implications of this vulnerability highlight the importance of proper kernel code review and testing, particularly for filesystem implementations that handle various operational modes including journaling and non-journaling configurations. This flaw demonstrates how seemingly minor implementation details in kernel code can result in significant security implications, emphasizing the need for comprehensive testing of edge cases and error conditions in operating system components. Security practitioners should also consider implementing monitoring solutions that can detect unusual filesystem behavior or system hangs that might indicate exploitation of this or similar vulnerabilities.