CVE-2025-68759: Linux Kernel Memory Leak Vulnerability

CVE-2025-68759 Overview

CVE-2025-68759 is a memory leak vulnerability in the Linux kernel's rtl818x Wi-Fi driver, specifically in the rtl8180_init_rx_ring() function. The driver allocates socket buffer (skb) packets and performs Direct Memory Access (DMA) allocations in a loop during receive ring initialization. When any allocation in the loop fails, the previously successful allocations are not released before the function returns. This leaves kernel memory and DMA-mapped regions unreclaimed, leading to resource exhaustion over repeated failure paths.

Critical Impact
Repeated initialization failures in the rtl8180 driver can exhaust kernel memory and DMA mapping resources, degrading system stability on hosts using affected Realtek wireless hardware.

Affected Products

Linux kernel rtl818x wireless driver (rtl8180 chipset support)
Multiple stable Linux kernel branches receiving the backport (see referenced kernel commits)
Systems using Realtek RTL8180-based Wi-Fi adapters

Discovery Timeline

2026-01-05 - CVE-2025-68759 published to NVD
2026-04-15 - Last updated in NVD database

Technical Details for CVE-2025-68759

Vulnerability Analysis

The issue resides in rtl8180_init_rx_ring() within the rtl818x driver, which sets up the receive descriptor ring for the RTL8180 PCI Wi-Fi chipset. The function iterates through ring entries, allocating an skb for each slot and mapping it for DMA. If any iteration fails midway, the function returns an error without unwinding prior allocations. Each leaked entry holds both an sk_buff structure and a DMA mapping, both of which are bounded kernel resources.

The upstream fix redirects error paths to an err_free_rings label that invokes rtl8180_free_rx_ring(), which properly walks the partially populated ring and releases each entry. The patch also removes the redundant free of rx_ring in the error path and sets the freed priv->rx_buf entry to NULL to prevent a double free when the cleanup helper later traverses the ring.

Root Cause

The root cause is incomplete error handling in a resource-allocation loop. The original implementation treated each allocation failure as a terminal condition without rolling back side effects from earlier iterations. This is a classic Memory Leak pattern compounded by a latent double-free risk if cleanup routines were invoked over the same entries.

Attack Vector

The leak triggers along the driver's initialization failure path. Triggering it requires conditions that cause dev_alloc_skb() or dma_map_single() to fail during ring setup, such as memory pressure or DMA address space exhaustion. An unprivileged local actor cannot directly invoke the path, but repeated driver bring-up cycles under constrained memory conditions can compound the leak. The vulnerability does not provide remote code execution; the impact is confined to resource exhaustion and kernel memory hygiene.

No public exploit code is available, and the issue has not been observed exploited in the wild. Technical details are documented in the upstream kernel commits referenced below.

Detection Methods for CVE-2025-68759

Indicators of Compromise

Kernel log messages from the rtl818x driver reporting allocation failures during interface bring-up
Growing Slab and SUnreclaim values in /proc/meminfo correlated with repeated Wi-Fi interface restarts
DMA mapping pressure visible through dmesg warnings on systems using RTL8180 hardware

Detection Strategies

Inventory running kernels with uname -r and compare against the fixed versions referenced in the kernel.org stable commits
Audit loaded modules for rtl818x and rtl8180 using lsmod to identify hosts exposed to the defective code path
Monitor for repeated ifconfig/ip link cycling on wireless interfaces backed by Realtek RTL8180 adapters

Monitoring Recommendations

Track kernel memory growth on long-running hosts that load the rtl818x driver
Alert on repeated driver probe failures recorded in journalctl -k
Forward kernel logs into a centralized analytics pipeline so allocation-failure patterns can be correlated across fleets

How to Mitigate CVE-2025-68759

Immediate Actions Required

Apply vendor kernel updates that incorporate the upstream fix for rtl8180_init_rx_ring()
Identify hosts loading the rtl818x module and prioritize them for patching
Unload the rtl818x module on systems that do not require RTL8180 wireless support

Patch Information

The fix routes error returns in rtl8180_init_rx_ring() through rtl8180_free_rx_ring() via an err_free_rings label, removes the duplicate rx_ring free, and clears priv->rx_buf entries to prevent double free. The patch has been backported across multiple stable branches. Refer to the upstream commits: Kernel Commit 3677c01, Kernel Commit 89caaaee, Kernel Commit 9b5b9c04, Kernel Commit a4fb7cca, Kernel Commit a813a745, Kernel Commit bf8513df, Kernel Commit c9d1c415, and Kernel Commit ee7db117.

Workarounds

Blacklist the rtl818x module on hosts that do not use RTL8180 hardware by adding blacklist rtl818x to /etc/modprobe.d/
Avoid repeatedly cycling the affected wireless interface under memory pressure until the patch is applied
Replace legacy RTL8180-based adapters with supported hardware on critical hosts where kernel upgrades are delayed

bash

# Verify whether the rtl818x driver is loaded and blacklist it if unused
lsmod | grep -E 'rtl818x|rtl8180'
echo 'blacklist rtl818x' | sudo tee /etc/modprobe.d/blacklist-rtl818x.conf
sudo modprobe -r rtl818x 2>/dev/null || true