CVE-2025-71146: Linux Kernel Memory Leak Vulnerability

CVE-2025-71146 Overview

A memory leak vulnerability has been identified in the Linux kernel's netfilter nf_conncount module. The flaw occurs when connection tracking (ct) objects are leaked through error paths that skip refcounted checks and return immediately. This vulnerability can lead to resource exhaustion and potential denial of service conditions on affected Linux systems.

Critical Impact

Memory leaks in the netfilter connection tracking subsystem can lead to kernel memory exhaustion, causing system instability and potential denial of service on Linux systems handling network traffic.

Affected Products

• Linux kernel (multiple stable branches affected)
• Systems utilizing netfilter connection tracking
• Network filtering and firewall implementations using nf_conncount

Discovery Timeline

• 2026-01-23 - CVE CVE-2025-71146 published to NVD
• 2026-01-26 - Last updated in NVD database

Technical Details for CVE-2025-71146

Vulnerability Analysis

The vulnerability resides in the nf_conncount module within the Linux kernel's netfilter subsystem. Connection tracking (ct) objects are reference-counted resources that must be properly managed to prevent memory leaks. The flaw occurs when error handling paths fail to perform the necessary refcounted checks before returning, causing ct objects to remain allocated without proper cleanup.

When the netfilter connection counting module processes connections, it allocates ct objects that track connection state. Under normal operation, these objects are properly released when no longer needed. However, certain error conditions cause the code to bypass the reference count verification, leaving ct objects orphaned in kernel memory.

Root Cause

The root cause is improper error handling in the nf_conncount module where certain error paths skip the refcounted check before returning. This means that when an error occurs during connection tracking operations, the code returns immediately without verifying whether the ct object needs to be released, leading to memory leaks.

The fix ensures that the refcounted check is always called regardless of the execution path, preventing ct objects from being leaked when errors occur.

Attack Vector

The attack vector for this vulnerability involves triggering error conditions in the netfilter connection counting subsystem. An attacker with the ability to generate network traffic that exercises the vulnerable code paths could potentially cause repeated memory leaks, eventually exhausting kernel memory resources.

The exploitation path involves:

• Generating network traffic that is processed by the nf_conncount module
• Triggering specific error conditions that cause the vulnerable code paths to execute
• Repeated exploitation leading to gradual kernel memory exhaustion

Due to the nature of kernel memory leaks, exploitation could result in degraded system performance, system instability, or denial of service conditions.

Detection Methods for CVE-2025-71146

Indicators of Compromise

• Unusual kernel memory consumption growth over time, particularly in netfilter-related allocations
• System logs indicating memory pressure or out-of-memory conditions
• Degraded network filtering performance
• Kernel slab allocator warnings related to connection tracking objects

Detection Strategies

• Monitor kernel memory allocation patterns using tools like /proc/slabinfo for netfilter-related objects
• Implement alerting on unusual growth in nf_conntrack memory usage
• Use kernel tracing tools to monitor nf_conncount module behavior during high-traffic scenarios
• Deploy SentinelOne Singularity platform for real-time kernel behavior monitoring and anomaly detection

Monitoring Recommendations

• Configure system monitoring to track kernel memory usage trends
• Set up alerts for connection tracking table exhaustion warnings
• Monitor system stability metrics and correlate with network traffic patterns
• Implement logging for netfilter subsystem errors and warnings

How to Mitigate CVE-2025-71146

Immediate Actions Required

• Update the Linux kernel to a patched version containing the fix
• Review system logs for signs of memory exhaustion related to netfilter
• Consider implementing connection rate limiting to reduce potential exploitation impact
• Monitor affected systems for stability issues until patches are applied

Patch Information

The Linux kernel maintainers have released patches across multiple stable branches to address this vulnerability. The fix ensures that the refcounted check is always performed before returning from error paths in the nf_conncount module.

Patches are available through the following kernel git commits:

• Kernel Git Commit 08fa37f
• Kernel Git Commit 0b88be7
• Kernel Git Commit 2e2a720
• Kernel Git Commit 325eb61
• Kernel Git Commit 4bd2b89
• Kernel Git Commit e1ac8dc
• Kernel Git Commit f381a33

Workarounds

• Implement connection rate limiting at the network perimeter to reduce traffic volume processed by nf_conncount
• Monitor and periodically restart affected services if memory exhaustion symptoms appear
• Consider temporarily disabling nf_conncount functionality if not critical to operations until patching is complete
• Configure memory limits and OOM killer policies to mitigate impact of potential memory exhaustion

# Monitor netfilter connection tracking memory usage
cat /proc/net/nf_conntrack | wc -l
cat /proc/sys/net/netfilter/nf_conntrack_count
cat /proc/sys/net/netfilter/nf_conntrack_max

# Check kernel slab allocations for connection tracking objects
slabtop -o | grep -i conntrack