CVE-2024-26642: Linux Kernel Netfilter Vulnerability

CVE-2024-26642 Overview

CVE-2024-26642 is a vulnerability in the Linux kernel's netfilter nf_tables subsystem that involves improper handling of anonymous sets with timeout flags. The vulnerability exists because the kernel did not properly reject anonymous sets with timeout flags from userspace, despite such combinations never being intended or used in legitimate operations. The only exception to this rule is NFT_SET_EVAL to ensure legacy meters continue to function.

This vulnerability allows a local attacker with low privileges to potentially cause a denial of service condition by exploiting the improper validation of anonymous set configurations in the netfilter framework.

Critical Impact

Local attackers can exploit improper input validation in nf_tables to trigger denial of service conditions affecting system availability.

Affected Products

• Linux Kernel (multiple versions)
• Debian Linux 10.0

Discovery Timeline

• 2024-03-21 - CVE-2024-26642 published to NVD
• 2025-03-13 - Last updated in NVD database

Technical Details for CVE-2024-26642

Vulnerability Analysis

The vulnerability resides in the nf_tables component of the Linux kernel's netfilter framework. Anonymous sets in nf_tables are internal data structures that are not meant to be directly manipulated by userspace applications with timeout configurations. However, the kernel failed to properly validate and reject such invalid configurations when they were submitted.

The netfilter framework is a critical networking subsystem in Linux that handles packet filtering, network address translation (NAT), and other packet mangling operations. The nf_tables component is the successor to the older iptables framework and provides a more flexible and efficient mechanism for packet classification.

When an attacker creates an anonymous set with the timeout flag enabled, the kernel should reject this configuration as invalid. The lack of this validation check could lead to unexpected behavior and potential denial of service conditions.

Root Cause

The root cause of this vulnerability is insufficient input validation in the nf_tables subsystem. Specifically, the code path that handles set creation did not include proper checks to reject anonymous sets when combined with timeout flags. This is an input validation error that allows userspace to submit configurations that were never intended to be valid.

The fix adds explicit validation to disallow anonymous sets with timeout flags, with a specific exception carved out for NFT_SET_EVAL to maintain backward compatibility with legacy meters functionality.

Attack Vector

This is a local attack vector vulnerability requiring low privileges. An attacker with local system access and the ability to interact with the netfilter subsystem (typically requiring CAP_NET_ADMIN capability or root privileges) could craft malicious nf_tables set configurations.

The attack involves:

1. Gaining local access to a vulnerable Linux system
2. Crafting an nf_tables rule that creates an anonymous set with the timeout flag enabled
3. Submitting this configuration to the kernel through the netlink interface
4. Triggering improper handling that leads to denial of service

The vulnerability does not affect confidentiality or integrity, but can impact system availability.

Detection Methods for CVE-2024-26642

Indicators of Compromise

• Unexpected system crashes or kernel panics related to netfilter operations
• Unusual nf_tables configuration attempts in system logs
• Audit logs showing netlink messages targeting nf_tables with suspicious set configurations
• System instability after netfilter rule modifications

Detection Strategies

• Monitor kernel logs for nf_tables-related errors or warnings using dmesg and journalctl
• Implement audit rules to track nft command usage and netlink socket operations
• Deploy SentinelOne Singularity Platform to detect anomalous kernel-level behavior and potential exploitation attempts
• Use system integrity monitoring to detect unauthorized kernel module loading or netfilter configuration changes

Monitoring Recommendations

• Enable auditd rules for monitoring nft binary execution and associated system calls
• Configure alerting for kernel oops or panic events related to netfilter components
• Monitor system resource usage for signs of denial of service conditions
• Implement centralized log collection for correlation of netfilter-related events across systems

How to Mitigate CVE-2024-26642

Immediate Actions Required

• Update Linux kernel to a patched version as soon as possible
• Review and restrict access to netfilter configuration capabilities using capabilities and namespaces
• Limit CAP_NET_ADMIN capability to trusted users and processes only
• Consider implementing additional access controls for systems running vulnerable kernels

Patch Information

The Linux kernel maintainers have released patches across multiple stable branches. The fix adds validation to reject anonymous sets with timeout flags while preserving backward compatibility for NFT_SET_EVAL used by legacy meters.

Patched commits are available from the Linux Kernel Git Repository. Additional patch commits have been backported to various stable kernel branches including commits 72c1efe3f247, 7cdc1be24cc1, and others.

Debian users should refer to the Debian LTS Security Announcements for distribution-specific patches.

Workarounds

• Restrict access to the nft command using file permissions or AppArmor/SELinux policies
• Implement network namespace isolation to limit netfilter access per container or application
• Use capability dropping to remove CAP_NET_ADMIN from non-essential processes
• Deploy monitoring to detect exploitation attempts while awaiting patches

# Restrict nft command access to root only
chmod 750 /usr/sbin/nft

# Verify kernel version and check for patches
uname -r
apt list --installed 2>/dev/null | grep linux-image

# For Debian/Ubuntu, update kernel packages
apt update && apt upgrade linux-image-$(uname -r)

# For RHEL/CentOS, update kernel
yum update kernel