CVE-2025-39882 Overview
CVE-2025-39882 is a use-after-free vulnerability in the Linux kernel's MediaTek Direct Rendering Manager (DRM) driver. The flaw stems from a bogus additional reference count decrement inside a for_each_child_of_node() iteration. The for_each_child_of_node() helper already drops the reference it takes to each node during iteration, so the extra of_node_put() call can trigger a use-after-free on Open Firmware (OF) device tree nodes. The issue affects Linux kernel versions 6.17-rc4 and 6.17-rc5, along with earlier stable branches receiving the same backported change. The vulnerability is tracked under CWE-416: Use After Free.
Critical Impact
A local, low-privileged attacker on a MediaTek-based Linux system could exploit the use-after-free to compromise kernel memory, potentially leading to privilege escalation or denial of service.
Affected Products
- Linux kernel 6.17-rc4
- Linux kernel 6.17-rc5
- Linux kernel stable branches receiving the backported drm/mediatek change
Discovery Timeline
- 2025-09-23 - CVE-2025-39882 published to the National Vulnerability Database (NVD)
- 2026-07-30 - Last updated in NVD database
Technical Details for CVE-2025-39882
Vulnerability Analysis
The vulnerability resides in the MediaTek DRM driver (drivers/gpu/drm/mediatek/) within the Linux kernel. The driver iterates over child device tree nodes using the for_each_child_of_node() macro to enumerate MediaTek display hardware components described in the Open Firmware device tree.
A recent change introduced an unnecessary of_node_put() call inside the loop body. Because the iterator macro already manages the reference count for each visited node, the additional decrement releases a reference the caller does not own. The freed OF node structure can then be dereferenced by subsequent code paths, satisfying the classic conditions for a use-after-free.
Exploitation requires local access with existing privileges on the target system, and it does not require user interaction. Successful abuse can corrupt kernel memory structures used by the device tree and DRM subsystems.
Root Cause
The root cause is incorrect reference counting on OF device tree nodes. Kernel reference-counted objects require balanced of_node_get() and of_node_put() calls. The added of_node_put() inside for_each_child_of_node() unbalanced this contract, driving the node's refcount to zero while the iterator still held a logical reference.
Attack Vector
An attacker must first obtain local, low-privileged access to a Linux system running an affected kernel on MediaTek hardware. Triggering the vulnerable code path requires interacting with the MediaTek DRM driver, typically through device probe, module load, or driver reinitialization events. Once the freed node memory is reused by the kernel allocator, subsequent dereferences may allow the attacker to influence kernel control flow or data, enabling privilege escalation or a system crash.
No public proof-of-concept exploit has been published for CVE-2025-39882 at the time of writing. Detailed technical context is available in the upstream fix commit c4901802 and companion stable backports.
Detection Methods for CVE-2025-39882
Indicators of Compromise
- Unexpected kernel oops or general protection fault messages referencing mediatek_drm, mtk_drm, or of_node_put in dmesg and /var/log/kern.log.
- KASAN (Kernel Address Sanitizer) reports flagging use-after-free access on device_node structures during DRM driver initialization.
- Kernel panics correlated with MediaTek display driver load or unload events.
Detection Strategies
- Inventory Linux hosts and identify systems running kernel 6.17-rc4, 6.17-rc5, or stable branches that received the drm/mediatek backport prior to the fix.
- Correlate crash telemetry from MediaTek-based devices with DRM subsystem stack traces to identify potential exploitation attempts.
- Deploy KASAN-enabled kernels in test environments to surface refcount imbalances early.
Monitoring Recommendations
- Forward kernel logs to a centralized logging platform and alert on repeated DRM-related faults on the same host.
- Monitor for anomalous local privilege escalation behavior, including unexpected root shells or capability changes following DRM driver activity.
- Track kernel package versions across the fleet to confirm patched builds are deployed.
How to Mitigate CVE-2025-39882
Immediate Actions Required
- Update to a Linux kernel build that includes the fix commits 4de37a48, b2fbe0f9, b58a26cd, or c4901802 from the mainline and stable trees.
- Restrict local access to MediaTek-based Linux systems and enforce least-privilege on interactive user accounts.
- Rebuild and redeploy any custom kernels that carry the offending backport without the corrective patch.
Patch Information
The upstream fix removes the erroneous of_node_put() call inside the for_each_child_of_node() loop in the MediaTek DRM driver. Patched commits are available at Kernel Git Commit 4de37a48, Kernel Git Commit b2fbe0f9, Kernel Git Commit b58a26cd, and Kernel Git Commit c4901802. Distribution vendors should ship these commits in their next kernel security update.
Workarounds
- If patching is delayed, unload the MediaTek DRM driver on systems that do not require display output using modprobe -r mediatek-drm and blacklist the module.
- Reduce exposure by limiting shell access, container escape surfaces, and untrusted local workloads on affected hardware until a patched kernel is deployed.
# Blacklist the MediaTek DRM module until a patched kernel is installed
echo "blacklist mediatek-drm" | sudo tee /etc/modprobe.d/blacklist-mediatek-drm.conf
sudo update-initramfs -u
sudo reboot
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
