CVE-2024-27397: Linux Kernel Privilege Escalation Flaw

CVE-2024-27397 Overview

CVE-2024-27397 is a Use-After-Free vulnerability in the Linux kernel's netfilter nf_tables subsystem. The vulnerability exists in the handling of set element timeouts during control plane transactions. Prior to the fix, set elements could expire while a control plane transaction was still in progress, leading to potential memory corruption and exploitation scenarios.

The vulnerability was addressed by introducing a timestamp field at the beginning of each transaction, stored in the nftables per-netns area. This ensures consistent timeout checking across set backend operations including .insert, .deactivate, and synchronous garbage collection paths.

Critical Impact

Local attackers with low privileges can exploit this Use-After-Free condition in the nf_tables subsystem to potentially achieve privilege escalation, execute arbitrary code with kernel privileges, or cause system instability.

Affected Products

• Linux Kernel versions prior to patch commits across multiple stable branches
• Linux Kernel 6.8-rc1, 6.8-rc2, and 6.8-rc3 release candidates
• Debian Linux (addressed in LTS announcements)

Discovery Timeline

• May 14, 2024 - CVE-2024-27397 published to NVD
• November 3, 2025 - Last updated in NVD database

Technical Details for CVE-2024-27397

Vulnerability Analysis

This Use-After-Free vulnerability (CWE-416) occurs in the Linux kernel's netfilter framework, specifically within the nf_tables set element timeout handling mechanism. The root issue stems from a race condition between the control plane transaction processing and element expiration checks.

When processing set operations, the kernel performs timeout validation at multiple points. The vulnerable code path allowed elements to transition to an expired state during an ongoing transaction, creating a window where freed memory could be accessed. The attack requires local access to the system with low privileges, though exploitation complexity is high due to the timing-sensitive nature of the race condition.

Successful exploitation can lead to complete compromise of confidentiality, integrity, and availability on the affected system, as kernel-level memory corruption can be leveraged for privilege escalation or arbitrary code execution within kernel context.

Root Cause

The root cause lies in the inconsistent use of time references when checking set element expiration. The original implementation used the current time for all timeout checks, including those in the control plane transaction path. This meant that between the start and end of a transaction, an element's timeout status could change, leading to operations being performed on already-freed memory structures.

The fix introduces a transaction-local timestamp stored in the nftables per-netns (network namespace) area. Control plane operations (.insert, .deactivate, sync GC) now use this consistent timestamp, while packet path operations (.lookup, .update) and asynchronous operations (async GC, .get, dump) continue using current time as appropriate for their lockless execution contexts.

Attack Vector

The vulnerability requires local access to the affected system. An attacker with low-privilege user access can craft specific netfilter rule configurations that trigger the race condition in the nf_tables timeout handling. The attack involves:

1. Creating nf_tables sets with elements that have short timeout values
2. Initiating control plane transactions that interact with these elements
3. Timing the operation to coincide with element expiration
4. Exploiting the resulting Use-After-Free condition for privilege escalation

The high attack complexity stems from the precise timing required to trigger the race condition between element expiration and transaction completion.

Detection Methods for CVE-2024-27397

Indicators of Compromise

• Unexpected kernel panics or oops messages referencing nf_tables, nft_set, or netfilter subsystem components
• Memory corruption warnings in kernel logs related to the netfilter namespace
• Unusual system instability coinciding with netfilter rule modifications
• Evidence of local privilege escalation attempts following netfilter operations

Detection Strategies

• Monitor kernel logs (dmesg, /var/log/kern.log) for KASAN (Kernel Address Sanitizer) reports indicating Use-After-Free in nf_tables code paths
• Implement audit rules for nft and iptables command invocations from unprivileged users
• Deploy kernel livepatching solutions to detect and alert on unpatched systems
• Use SentinelOne's kernel-level behavioral monitoring to detect anomalous netfilter subsystem interactions

Monitoring Recommendations

• Enable kernel auditing for netfilter configuration changes using auditctl -w /etc/nftables.conf
• Configure alerting for any user-space processes making direct netlink calls to the netfilter subsystem
• Monitor for processes attempting to load or manipulate nf_tables rules outside of normal administrative operations
• Track system memory integrity using available kernel hardening features

How to Mitigate CVE-2024-27397

Immediate Actions Required

• Update the Linux kernel to a patched version containing the timestamp-based timeout fix
• Restrict access to netfilter/nftables configuration to only trusted administrative accounts
• Consider temporarily disabling nf_tables functionality if not required and patching is delayed
• Audit existing nftables rules for any suspicious configurations that may have been added by attackers

Patch Information

The Linux kernel development team has released patches across multiple stable kernel branches. The fix introduces a timestamp field at the transaction start, ensuring consistent timeout behavior during control plane operations. Patches are available through the following kernel commits:

• Kernel Commit 0d40e8cb1d1f
• Kernel Commit 383182db8d58
• Kernel Commit 7395dfacfff6
• Kernel Commit 7b17de2a71e5
• Kernel Commit 7fa2e2960fff
• Kernel Commit b45176b86967
• Kernel Commit eaf1a29ea5d7
• Kernel Commit f8dfda798650

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

Workarounds

• Limit netfilter/nftables access using Linux capabilities, removing CAP_NET_ADMIN from untrusted users and processes
• Apply kernel module parameter restrictions to limit nf_tables functionality if the feature is not essential
• Use containerization with restricted network namespaces to isolate potentially vulnerable workloads
• Implement mandatory access control (SELinux/AppArmor) policies restricting nftables operations

# Restrict nftables access to root only
chmod 700 /usr/sbin/nft
# Remove CAP_NET_ADMIN from non-essential processes
setcap -r /path/to/untrusted/binary
# Verify kernel version contains the fix
uname -r