CVE-2013-1767 in Linux
Summary
by MITRE
Use-after-free vulnerability in the shmem_remount_fs function in mm/shmem.c in the Linux kernel before 3.7.10 allows local users to gain privileges or cause a denial of service (system crash) by remounting a tmpfs filesystem without specifying a required mpol (aka mempolicy) mount option.
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Analysis
by VulDB Data Team • 05/05/2021
The CVE-2013-1767 vulnerability represents a critical use-after-free flaw in the Linux kernel's shared memory implementation that affects systems running kernel versions prior to 3.7.10. This vulnerability specifically resides within the shmem_remount_fs function located in the mm/shmem.c file, which handles the remounting of tmpfs filesystems. The issue arises when a local user attempts to remount a tmpfs filesystem without providing the necessary mempolicy mount option, creating a scenario where freed memory is accessed after deallocation. The vulnerability is classified under CWE-416 as a use-after-free condition, which is a well-known class of memory safety issues that can lead to arbitrary code execution or system instability.
The technical exploitation of this vulnerability occurs during the remount operation of tmpfs filesystems where the kernel fails to properly validate or initialize memory structures before proceeding with the remount process. When a user remounts a tmpfs without specifying the required mpol option, the kernel's memory management subsystem enters an inconsistent state where previously allocated memory structures are freed but subsequently accessed during the remount operation. This memory access violation can result in either a system crash due to segmentation faults or more critically, provide an attacker with the opportunity to escalate privileges by manipulating the freed memory contents. The vulnerability operates at the kernel level, making it particularly dangerous as it can be exploited by any local user with access to the system.
The operational impact of CVE-2013-1767 extends beyond simple denial of service scenarios to encompass potential privilege escalation capabilities that align with ATT&CK technique T1068 for privilege escalation through local exploitation. Systems running affected kernel versions are vulnerable to both system crashes that disrupt normal operations and potential security breaches where local users could leverage this flaw to gain elevated privileges. The vulnerability affects any Linux system that utilizes tmpfs filesystems and allows for remount operations without proper mempolicy specification, which is common in various system configurations and user environments. The exploitability is relatively straightforward since it only requires local access and basic knowledge of filesystem remount operations, making it particularly concerning for multi-user systems or environments where privilege separation is not properly enforced.
Mitigation strategies for CVE-2013-1767 focus primarily on upgrading to kernel versions 3.7.10 or later where the vulnerability has been patched. System administrators should prioritize updating their kernel installations to address this memory safety issue. Additionally, implementing proper filesystem mount options and ensuring that all tmpfs remount operations specify required mempolicy parameters can help reduce the attack surface. The patch for this vulnerability involves proper memory initialization and validation checks within the shmem_remount_fs function to prevent access to freed memory structures. Organizations should also consider implementing monitoring solutions to detect unusual filesystem remount activities that might indicate exploitation attempts, as the vulnerability requires specific conditions to be met for successful exploitation. Security hardening practices including restricting local user privileges and implementing proper access controls can further reduce the risk associated with this vulnerability.