CVE-2025-68759: Linux Kernel Use-After-Free Vulnerability

CVE-2025-68759 Overview

A memory leak vulnerability has been identified in the Linux kernel's rtl818x WiFi driver, specifically in the rtl8180_init_rx_ring() function. The vulnerability occurs when memory is allocated for skb packets and DMA allocations in a loop, and if an allocation fails, previously successful allocations are not properly freed on exit. This can lead to memory exhaustion over time, potentially causing system instability or denial of service conditions.

Critical Impact

Memory leaks in kernel drivers can lead to system resource exhaustion, degraded performance, and potential denial of service on affected Linux systems with Realtek RTL8180/RTL8185 WiFi hardware.

Affected Products

• Linux kernel with rtl818x WiFi driver enabled
• Systems using Realtek RTL8180/RTL8185 wireless chipsets
• Linux kernel versions prior to the security patches

Discovery Timeline

• January 5, 2026 - CVE-2025-68759 published to NVD
• January 8, 2026 - Last updated in NVD database

Technical Details for CVE-2025-68759

Vulnerability Analysis

The vulnerability exists within the rtl8180_init_rx_ring() function of the rtl818x WiFi driver. During initialization, the function allocates memory for socket buffer (skb) packets and performs DMA allocations in a loop. The flaw arises from improper error handling: when a memory allocation fails mid-loop, the function exits without freeing the previously allocated resources.

This memory leak can be triggered during driver initialization when memory pressure exists on the system. Each failed initialization attempt that doesn't properly clean up previous allocations contributes to gradual memory exhaustion. Additionally, the original code path contained a potential double-free condition where rx_ring could be freed twice if not handled correctly.

Root Cause

The root cause is improper resource cleanup in the error handling path of rtl8180_init_rx_ring(). When a memory allocation fails within the loop that creates skb packets and DMA mappings, the error path did not call rtl8180_free_rx_ring() to release previously allocated buffers. Furthermore, the freed priv->rx_buf entries were not set to NULL after being freed, creating conditions for a potential double-free vulnerability.

Attack Vector

This vulnerability requires local access to a system running the affected rtl818x driver. An attacker with local access could potentially trigger repeated driver initialization failures under controlled memory pressure conditions, gradually exhausting system memory. While not directly exploitable for code execution, sustained memory leaks can degrade system performance and eventually cause denial of service.

The fix addresses these issues by:

1. Jumping to the err_free_rings label on error, which properly calls rtl8180_free_rx_ring() to release all prior allocations
2. Removing the redundant free of rx_ring in the error path
3. Setting freed priv->rx_buf entries to NULL to prevent double-free conditions

Detection Methods for CVE-2025-68759

Indicators of Compromise

• Gradual memory consumption increase on systems with RTL8180/RTL8185 WiFi hardware
• Kernel memory warnings or OOM (Out of Memory) killer activations related to network subsystem
• Repeated WiFi driver initialization failures in system logs
• System instability or crashes following WiFi connection attempts

Detection Strategies

• Monitor kernel logs for rtl818x driver initialization errors using dmesg | grep -i rtl818
• Implement memory usage monitoring on systems with affected Realtek WiFi hardware
• Use kernel memory debugging tools such as KASAN (Kernel Address Sanitizer) to detect memory leaks
• Deploy SentinelOne agents to monitor for anomalous memory consumption patterns in kernel space

Monitoring Recommendations

• Enable kernel memory leak detection debugging options in development/test environments
• Configure alerting for sustained memory growth on systems with rtl818x driver loaded
• Monitor /proc/meminfo for unexpected MemFree decreases correlated with WiFi activity
• Use slabtop to monitor kernel slab allocator for abnormal growth in network-related caches

How to Mitigate CVE-2025-68759

Immediate Actions Required

• Update the Linux kernel to a version containing the security patches
• If updates cannot be immediately applied, consider temporarily disabling the rtl818x driver if the WiFi hardware is not essential
• Monitor affected systems for memory exhaustion symptoms
• Reboot affected systems to reclaim leaked memory as a temporary measure

Patch Information

The Linux kernel development team has released patches to address this vulnerability. The fix modifies the error handling in rtl8180_init_rx_ring() to properly release allocated resources when initialization fails. Multiple kernel stable branches have received updates:

• Kernel Git Commit 9b5b9c04
• Kernel Git Commit a813a745
• Kernel Git Commit c9d1c415
• Kernel Git Commit ee7db117

Apply the appropriate patch for your kernel version by updating through your distribution's package manager or by compiling a patched kernel from source.

Workarounds

• Blacklist the rtl818x driver module if the WiFi hardware is not required: add blacklist rtl818x_pci to /etc/modprobe.d/blacklist.conf
• Use an alternative WiFi adapter with a different chipset that does not rely on the affected driver
• Implement automated system reboots during maintenance windows to clear accumulated memory leaks
• Deploy monitoring scripts to alert administrators before memory exhaustion becomes critical

# Configuration example
# Blacklist the affected rtl818x driver to prevent loading
echo "blacklist rtl818x_pci" | sudo tee /etc/modprobe.d/blacklist-rtl818x.conf

# Remove the driver if currently loaded
sudo modprobe -r rtl818x_pci

# Verify the driver is not loaded
lsmod | grep rtl818x