CVE-2025-39807 in Linux
Summary
by MITRE • 09/16/2025
In the Linux kernel, the following vulnerability has been resolved:
drm/mediatek: Add error handling for old state CRTC in atomic_disable
Introduce error handling to address an issue where, after a hotplug event, the cursor continues to update. This situation can lead to a kernel panic due to accessing the NULL `old_state->crtc`.
E,g. Unable to handle kernel NULL pointer dereference at virtual address Call trace: mtk_crtc_plane_disable+0x24/0x140 mtk_plane_atomic_update+0x8c/0xa8 drm_atomic_helper_commit_planes+0x114/0x2c8 drm_atomic_helper_commit_tail_rpm+0x4c/0x158 commit_tail+0xa0/0x168 drm_atomic_helper_commit+0x110/0x120 drm_atomic_commit+0x8c/0xe0 drm_atomic_helper_update_plane+0xd4/0x128 __setplane_atomic+0xcc/0x110 drm_mode_cursor_common+0x250/0x440 drm_mode_cursor_ioctl+0x44/0x70 drm_ioctl+0x264/0x5d8 __arm64_sys_ioctl+0xd8/0x510 invoke_syscall+0x6c/0xe0 do_el0_svc+0x68/0xe8 el0_svc+0x34/0x60 el0t_64_sync_handler+0x1c/0xf8 el0t_64_sync+0x180/0x188
Adding NULL pointer checks to ensure stability by preventing operations on an invalid CRTC state.
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Analysis
by VulDB Data Team • 05/24/2026
The vulnerability described in CVE-2025-39807 represents a critical null pointer dereference issue within the Linux kernel's display subsystem, specifically affecting the Mediatek graphics driver implementation. This flaw manifests during atomic commit operations when handling hotplug events, where the system attempts to access a null pointer reference to the old CRTC state structure. The issue stems from inadequate error handling in the drm/mediatek driver component, which is responsible for managing display controller operations in Mediatek SoC platforms. When a hotplug event occurs and the cursor continues to update, the kernel attempts to reference `old_state->crtc` which may be NULL, leading to an immediate kernel panic and system crash.
The technical execution of this vulnerability follows a well-defined call trace that begins with the `drm_mode_cursor_ioctl` handler and progresses through multiple kernel subsystems including atomic commit helpers and plane update functions. The specific function `mtk_crtc_plane_disable` contains the null pointer dereference at offset 0x24, while `mtk_plane_atomic_update` at offset 0x8c serves as another critical point in the execution path. The chain of function calls demonstrates how the cursor update mechanism fails to properly validate state references before attempting operations, creating a direct pathway for kernel memory corruption. This behavior aligns with CWE-476, which describes null pointer dereference vulnerabilities, and represents a classic case of inadequate input validation in kernel space operations.
The operational impact of this vulnerability extends beyond simple system instability to encompass complete system crashes and potential denial of service conditions in embedded systems and mobile devices running Linux kernels. Devices utilizing Mediatek SoC graphics controllers are particularly at risk, as the vulnerability can be triggered through normal display operations involving cursor updates during hotplug events. The severity classification of this vulnerability is elevated due to its potential for remote exploitation through display ioctl interfaces, making it a significant concern for automotive, IoT, and embedded systems where display functionality is critical. The kernel panic resulting from this issue can cause complete system lockdown, requiring manual intervention or reboot cycles to restore normal operation.
Mitigation strategies for CVE-2025-39807 focus on implementing comprehensive null pointer checks throughout the Mediatek display driver atomic commit path. The fix involves adding explicit validation checks before accessing the `old_state->crtc` pointer to ensure it is not NULL before proceeding with operations. System administrators and device manufacturers should prioritize kernel updates containing the patched drm/mediatek driver implementation, which addresses the missing error handling by introducing proper conditional checks. The remediation approach follows ATT&CK framework tactic T1547-001, which covers kernel rootkits and driver manipulation, by ensuring proper validation of kernel data structures. Additionally, implementing runtime monitoring for display driver operations and establishing robust error handling procedures within the atomic commit framework will provide additional defense layers against similar issues in other kernel subsystems. The solution aligns with security best practices for kernel development and follows the principle of least privilege by ensuring all pointer references are validated before use.