CVE-2024-26925: Linux Kernel Race Condition Vulnerability

CVE-2024-26925 Overview

CVE-2024-26925 is a race condition vulnerability in the Linux kernel's netfilter subsystem, specifically within the nf_tables component. The vulnerability occurs when the commit mutex is improperly released during a critical section between nft_gc_seq_begin() and nft_gc_seq_end() function calls. This premature mutex release allows an asynchronous garbage collection (GC) worker to collect expired objects and acquire the released commit lock within the same GC sequence, leading to potential system instability and denial of service conditions.

The issue stems from the nf_tables_module_autoload() function, which temporarily releases the mutex to load module dependencies before replaying the transaction. The fix moves this operation to occur after nft_gc_seq_end() is called during the abort phase, ensuring proper synchronization.

Critical Impact

Local attackers with low privileges can exploit this race condition to cause system denial of service through kernel crashes or resource corruption in the netfilter subsystem.

Affected Products

• Linux Kernel (multiple versions including 6.5 and 6.9 release candidates)
• Debian Linux 10.0

Discovery Timeline

• April 25, 2024 - CVE-2024-26925 published to NVD
• December 23, 2025 - Last updated in NVD database

Technical Details for CVE-2024-26925

Vulnerability Analysis

This vulnerability exists in the Linux kernel's netfilter nf_tables implementation where improper mutex handling creates a race condition. The core issue involves the commit mutex, which protects critical operations during garbage collection sequences. When processing transactions that require module autoloading, the nf_tables_module_autoload() function temporarily releases this mutex to load dependencies from user space.

The problem occurs during the abort path: if the mutex is released while still within the critical section bounded by nft_gc_seq_begin() and nft_gc_seq_end(), an asynchronous GC worker running on another CPU can observe this state, collect expired objects, and acquire the commit lock. This leads to inconsistent state where the GC worker operates on objects that the abort path expects to still be protected, potentially causing use-after-free conditions or other memory corruption issues.

The vulnerability requires local access and low privileges to trigger, as it involves manipulating netfilter rules which typically requires CAP_NET_ADMIN capability. The impact is primarily denial of service through kernel panics or system hangs.

Root Cause

The root cause is improper synchronization in the nf_tables abort path. The nf_tables_module_autoload() function was positioned incorrectly within the transaction abort sequence, releasing the commit mutex while nft_gc_seq_begin() was still active. This violated the invariant that the mutex must be held continuously between nft_gc_seq_begin() and nft_gc_seq_end() to prevent the GC worker from interfering with the transaction state.

Attack Vector

The attack vector is local, requiring an attacker to have access to the system with permissions to manipulate netfilter rules. The exploitation scenario involves:

1. Triggering a transaction that requires module autoloading in the netfilter subsystem
2. Timing the abort path to coincide with GC worker activity
3. Racing the mutex release to cause the GC worker to collect objects during the critical section

The vulnerability manifests in the mutex handling logic within the nf_tables abort path. When nf_tables_module_autoload() is called during abort processing, it releases the commit_mutex to allow module loading from userspace. If an async GC worker is active during this window, it can acquire the mutex and collect expired objects that should still be protected. The fix relocates the module autoload call to occur after nft_gc_seq_end() completes, ensuring the GC sequence is properly finalized before releasing the mutex. See the Linux kernel commit 0d459e2 for the complete fix implementation.

Detection Methods for CVE-2024-26925

Indicators of Compromise

• Unexpected kernel panics or oops messages referencing nf_tables or netfilter components
• System log entries showing nft_gc related errors or warnings
• Kernel crash dumps indicating race conditions in netfilter subsystem

Detection Strategies

• Monitor kernel logs for netfilter-related errors using dmesg | grep -i nf_tables
• Implement kernel tracing on nft_gc_seq_begin() and nft_gc_seq_end() functions to detect anomalous timing patterns
• Deploy SentinelOne agents to detect kernel-level exploitation attempts targeting netfilter subsystems

Monitoring Recommendations

• Enable kernel auditing for netfilter rule modifications using auditd
• Configure system monitoring to alert on kernel crash events
• Use SentinelOne's Linux agent to monitor for suspicious privilege escalation attempts that may precede exploitation

How to Mitigate CVE-2024-26925

Immediate Actions Required

• Update Linux kernel to a patched version immediately
• Review system access controls to limit users with CAP_NET_ADMIN capability
• Monitor affected systems for signs of exploitation or system instability
• Consider temporarily restricting netfilter rule modifications on critical systems

Patch Information

Linux kernel maintainers have released patches across multiple stable branches. Apply the appropriate patch for your kernel version:

• Linux Kernel Commit 0d459e2
• Linux Kernel Commit 2cee2ff
• Linux Kernel Commit 61ac728
• Linux Kernel Commit 8038ee3
• Linux Kernel Commit 8d3a58a
• Linux Kernel Commit a34ba4b
• Linux Kernel Commit eb769ff

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

Workarounds

• Restrict access to netfilter administration by limiting CAP_NET_ADMIN capability to trusted users only
• Use network namespaces to isolate untrusted workloads from netfilter rule manipulation
• Implement monitoring for suspicious netfilter-related system calls using seccomp or auditd

# Verify current kernel version and check for vulnerability
uname -r

# Check for available kernel updates (Debian/Ubuntu)
apt update && apt list --upgradable | grep linux

# Check for available kernel updates (RHEL/CentOS)
yum check-update kernel

# Restrict CAP_NET_ADMIN capability (requires root)
# Review users with netfilter capabilities
getent passwd | while read line; do
  user=$(echo $line | cut -d: -f1)
  capsh --decode=$(grep Cap /proc/$(id -u $user 2>/dev/null)/status 2>/dev/null | grep CapEff | awk '{print $2}') 2>/dev/null | grep -q net_admin && echo "User $user has CAP_NET_ADMIN"
done