CVE-2025-71186 Overview
A memory leak vulnerability has been identified in the Linux kernel's STM32 DMA multiplexer (dmamux) driver. The vulnerability occurs during route allocation when the driver looks up the DMA mux platform device but fails to properly drop the reference taken during that lookup operation. This reference leak can lead to resource exhaustion over time.
Critical Impact
Improper device reference handling in the STM32 dmamux driver can cause memory leaks and potential resource exhaustion on affected embedded systems.
Affected Products
- Linux kernel with STM32 DMA engine support
- Systems utilizing STM32 microcontrollers with DMA multiplexer functionality
- Embedded devices running affected Linux kernel versions with dmaengine subsystem enabled
Discovery Timeline
- 2026-01-31 - CVE CVE-2025-71186 published to NVD
- 2026-02-03 - Last updated in NVD database
Technical Details for CVE-2025-71186
Vulnerability Analysis
This vulnerability exists within the dmaengine/stm32/dmamux component of the Linux kernel. When the DMA multiplexer driver performs route allocation, it looks up the DMA mux platform device and takes a reference to it. However, the code path fails to release this reference when appropriate, causing a device reference leak.
The kernel documentation notes that holding a reference to a device does not prevent its driver data from becoming invalid, which means the reference serves no functional purpose while still consuming resources. Each route allocation without proper reference release accumulates unreleased device references, potentially leading to memory exhaustion on systems with frequent DMA operations.
Root Cause
The root cause is improper reference counting in the STM32 dmamux driver's route allocation code path. When platform_device_get() or similar lookup functions are used to obtain a reference to the DMA mux device, the corresponding platform_device_put() or put_device() call is missing, violating the kernel's reference counting contract for device objects.
Attack Vector
This vulnerability is a local kernel issue that manifests during normal DMA operations on STM32-based systems. An attacker with local access could potentially trigger excessive DMA route allocations to accelerate resource exhaustion. However, exploitation typically requires privileged access to device drivers or the ability to influence DMA operations on the affected platform.
The vulnerability mechanism involves the improper handling of device references in the dmaengine/stm32/dmamux subsystem. When the driver allocates a route for DMA channels, it retrieves a reference to the platform device but fails to decrement the reference count when the reference is no longer needed. For technical details, refer to the kernel patch commits that address this issue.
Detection Methods for CVE-2025-71186
Indicators of Compromise
- Increasing kernel memory usage over time on systems with active DMA operations
- Device reference count warnings or errors in kernel logs related to STM32 dmamux
- System instability or performance degradation on embedded STM32-based platforms after extended operation
Detection Strategies
- Monitor kernel memory allocation metrics for gradual increases without corresponding deallocations
- Implement kernel debugging tools such as kmemleak to detect unreleased device references
- Review kernel logs for dmamux-related warnings using dmesg | grep -i dmamux
- Use SentinelOne Singularity platform to monitor for anomalous kernel memory patterns
Monitoring Recommendations
- Deploy SentinelOne agents on embedded Linux systems utilizing STM32 DMA functionality
- Enable kernel memory debugging features during testing and development phases
- Establish baseline memory usage patterns to detect gradual resource leaks
- Configure alerts for sustained memory growth on affected embedded systems
How to Mitigate CVE-2025-71186
Immediate Actions Required
- Apply the latest kernel patches that address the device reference leak in the STM32 dmamux driver
- Schedule maintenance windows for embedded systems to apply kernel updates
- Consider rebooting affected systems periodically as a temporary measure to release accumulated references
- Review DMA usage patterns to identify systems most at risk of resource exhaustion
Patch Information
Multiple kernel patches have been released to address this vulnerability. The fixes ensure that the device reference taken during DMA mux platform device lookup is properly dropped after route allocation. The patches are available through the following kernel commits:
- Kernel Patch Commit 1a179ac
- Kernel Patch Commit 2fb1025
- Kernel Patch Commit 3ef52d3
- Kernel Patch Commit dd6e494
Workarounds
- Implement periodic system reboots to clear accumulated device references as a temporary mitigation
- Limit DMA route allocation frequency where operationally feasible
- Monitor system resources closely and restart services that heavily utilize DMA when memory thresholds are reached
- Consider disabling unused DMA channels to reduce the attack surface
# Configuration example
# Check current kernel version for STM32 dmamux support
uname -r
# Verify dmamux module status
lsmod | grep stm32
# Monitor kernel memory for potential leaks
cat /proc/meminfo | grep -E "MemFree|MemAvailable|Slab"
# Check kernel logs for dmamux-related issues
dmesg | grep -i "dmamux\|dmaengine\|stm32"
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
