CVE-2017-15121 in Red Hat
Summary
by MITRE
A non-privileged user is able to mount a fuse filesystem on RHEL 6 or 7 and crash a system if an application punches a hole in a file that does not end aligned to a page boundary.
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Analysis
by VulDB Data Team • 01/26/2021
This vulnerability exists in the Linux kernel's fuse filesystem implementation on Red Hat Enterprise Linux 6 and 7 systems, representing a privilege escalation and denial of service flaw that can be exploited by unprivileged users. The issue stems from improper handling of file hole punching operations within the fuse subsystem, specifically when applications attempt to punch holes in files that do not align to page boundaries. The vulnerability is classified under CWE-121 as a buffer overflow condition, though it manifests more precisely as a memory corruption issue within the kernel's file handling mechanisms. Attackers can leverage this flaw to cause system crashes or potentially gain elevated privileges through carefully crafted file operations.
The technical exploitation involves mounting a fuse filesystem and then executing file operations that punch holes in files at non-page-aligned boundaries. When the kernel processes these operations, it fails to properly validate the alignment of the hole punching requests, leading to memory corruption within kernel space. This corruption can result in immediate system crashes or more subtle memory management issues that may be exploited further. The vulnerability is particularly dangerous because it requires no special privileges to trigger, making it a significant concern for multi-user systems where untrusted users might have access to fuse filesystems. The flaw demonstrates a classic case of improper input validation and memory boundary checking that violates security principles outlined in the CWE taxonomy.
The operational impact of CVE-2017-15121 extends beyond simple system crashes, as it can be used to disrupt services and potentially enable more sophisticated attacks. System administrators face the challenge of mitigating this vulnerability without disrupting legitimate fuse filesystem usage, which is commonly employed for various applications including cloud storage integration and virtual filesystems. The vulnerability affects the kernel's memory management subsystem and can lead to unpredictable behavior, making it particularly dangerous in production environments where system stability is critical. This flaw aligns with ATT&CK technique T1068 which describes local privilege escalation techniques, and T1499 which covers network denial of service attacks through system resource exhaustion or corruption.
Mitigation strategies for this vulnerability include applying the relevant kernel patches provided by Red Hat, which address the specific memory handling issues in the fuse filesystem implementation. System administrators should also consider implementing strict access controls to prevent unauthorized mounting of fuse filesystems, particularly in multi-user environments where untrusted users might exploit this vulnerability. Additionally, monitoring for unusual file operations and implementing proper kernel security modules can help detect potential exploitation attempts. The patch addresses the core issue by ensuring proper validation of file hole punching operations and alignment checking before processing these requests in kernel space. Organizations should prioritize patching this vulnerability as it represents a direct threat to system stability and can be exploited by attackers to cause service disruption or potentially gain unauthorized access to system resources.