CVE-2023-4244 in Linux
Summary
by MITRE • 09/06/2023
A use-after-free vulnerability in the Linux kernel's netfilter: nf_tables component can be exploited to achieve local privilege escalation.
Due to a race condition between nf_tables netlink control plane transaction and nft_set element garbage collection, it is possible to underflow the reference counter causing a use-after-free vulnerability.
We recommend upgrading past commit 3e91b0ebd994635df2346353322ac51ce84ce6d8.
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Analysis
by VulDB Data Team • 10/02/2023
The vulnerability identified as CVE-2023-4244 represents a critical use-after-free condition within the Linux kernel's netfilter nf_tables subsystem, specifically affecting the nft_set element management functionality. This flaw exists within the kernel's networking stack and poses a significant threat to system security. The vulnerability stems from a race condition that occurs between the netlink control plane transaction processing and the garbage collection mechanism responsible for managing nft_set elements. The race condition creates a temporal window where the reference counter for nft_set elements can be manipulated in a way that leads to improper memory management, ultimately resulting in a use-after-free scenario.
The technical exploitation of this vulnerability requires an attacker with local access to the system, as it operates within the kernel space and leverages the nf_tables subsystem's handling of network filtering rules. The race condition manifests when a netlink transaction processes an nft_set element while the garbage collector simultaneously attempts to clean up the same element, creating a scenario where the reference counter underflows and becomes negative. This improper reference counting leads to the kernel attempting to free memory that has already been freed or is in an invalid state, creating a use-after-free condition that can be exploited to execute arbitrary code with kernel privileges. The vulnerability is classified under CWE-416 as a use-after-free error, and the exploitation pattern aligns with techniques described in the ATT&CK framework under T1068 for local privilege escalation.
The operational impact of this vulnerability extends beyond simple local privilege escalation, as successful exploitation can lead to complete system compromise and persistent access. The attacker can leverage the use-after-free condition to gain kernel-level privileges, enabling them to bypass security controls, escalate their access to other users or processes, and potentially establish persistence within the system. The attack surface is limited to systems running Linux kernels with nf_tables support and where local users have the ability to interact with the netfilter subsystem. The vulnerability affects various kernel versions and can be particularly dangerous in multi-user environments or systems where local access cannot be strictly controlled. Organizations running affected kernel versions face significant risk, as the exploitation chain is relatively straightforward once local access is obtained.
Mitigation strategies for CVE-2023-4244 primarily involve upgrading the Linux kernel to a version that includes the fix for the race condition in the nf_tables subsystem. The recommended approach is to upgrade past commit 3e91b0ebd994635df2346353322ac51ce84ce6d8, which contains the necessary patches to address the reference counter underflow issue. System administrators should prioritize kernel updates, particularly in production environments where the vulnerability could be exploited by malicious actors. Additionally, organizations should implement monitoring for suspicious netfilter activity and consider implementing access controls to limit local user privileges where possible. The vulnerability highlights the importance of proper synchronization mechanisms in kernel code and demonstrates how seemingly minor race conditions can lead to critical security flaws. Regular kernel security audits and adherence to security best practices for kernel development are essential to prevent similar issues in the future. Organizations should also consider implementing kernel lockdown mechanisms and other security hardening measures to limit the potential impact of such vulnerabilities.