CVE-2016-4913 in Linux
Summary
by MITRE • 01/25/2023
The get_rock_ridge_filename function in fs/isofs/rock.c in the Linux kernel before 4.5.5 mishandles NM (aka alternate name) entries containing \0 characters, which allows local users to obtain sensitive information from kernel memory or possibly have unspecified other impact via a crafted isofs filesystem.
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Analysis
by VulDB Data Team • 01/25/2023
The vulnerability identified as CVE-2016-4913 resides within the Linux kernel's ISO filesystem implementation, specifically in the get_rock_ridge_filename function located in fs/isofs/rock.c. This flaw affects Linux kernel versions prior to 4.5.5 and represents a significant security issue that could potentially expose sensitive kernel memory to local users. The vulnerability stems from improper handling of NM (alternate name) entries that contain null characters, creating a condition where the kernel fails to properly validate or process these specific filesystem entries. The rock ridge extension is a set of conventions used in ISO 9660 filesystems to provide additional metadata and features beyond the standard filesystem specification, and the NM entry type specifically defines alternate names for files and directories within the filesystem.
The technical flaw manifests when the kernel processes ISO filesystems containing crafted NM entries with null character sequences. During the filename extraction process, the get_rock_ridge_filename function does not adequately sanitize or validate the presence of null characters within these alternate name entries, leading to potential buffer overflows or memory corruption scenarios. This improper handling can cause the kernel to read beyond the intended memory boundaries or access uninitialized memory regions, resulting in information disclosure vulnerabilities. The null character handling issue creates a path where attackers can craft malicious ISO filesystems that, when mounted, trigger the vulnerable code path and cause the kernel to expose kernel memory contents to user-space processes. This type of vulnerability falls under the CWE-121 category of Stack-based Buffer Overflow, as the improper handling of string data can lead to memory corruption.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides local attackers with a potential means to extract sensitive kernel memory contents that may contain cryptographic keys, passwords, or other confidential information. The unspecified other impacts mentioned in the vulnerability description suggest that the memory corruption could potentially lead to system instability or even privilege escalation under certain conditions. Attackers could leverage this vulnerability by creating specially crafted ISO filesystems with malicious NM entries containing null characters, then mounting these filesystems on target systems. The vulnerability is particularly concerning because it operates at the kernel level, meaning that successful exploitation could provide attackers with access to kernel memory spaces that are normally protected from user-space access. This aligns with ATT&CK technique T1059.001 for command and scripting interpreter and T1068 for exploit for privilege escalation, as the information disclosure could be used as a stepping stone for further attacks.
Mitigation strategies for CVE-2016-4913 primarily focus on kernel version updates, with the most effective solution being the upgrade to Linux kernel version 4.5.5 or later where the vulnerability has been patched. System administrators should also implement strict filesystem mounting policies that prevent untrusted ISO images from being automatically mounted, particularly in environments where user-generated content or unverified filesystems may be present. The patch for this vulnerability typically involves adding proper validation checks for null characters in NM entries and ensuring that the filename extraction process properly handles edge cases. Additional mitigations include implementing proper filesystem access controls, monitoring for suspicious ISO mounting activities, and applying the principle of least privilege when handling filesystem operations. Organizations should also consider implementing kernel lockdown mechanisms and other security hardening measures to reduce the potential impact of such vulnerabilities. The vulnerability demonstrates the importance of proper input validation in kernel space code and highlights the critical nature of maintaining up-to-date kernel versions to protect against known vulnerabilities.