CVE-2026-68439 Overview
CVE-2026-68439 is a NULL pointer dereference vulnerability in the Linux kernel's MediaTek mt7925 Wi-Fi driver. The flaw resides in the mt7925_mcu_bss_he_tlv() function, which calls mt76_connac_get_he_phy_cap() and dereferences the returned cap pointer without validating it. Because mt76_connac_get_he_phy_cap can theoretically return NULL, the unchecked dereference can trigger a kernel oops and destabilize the system. The issue affects Linux kernel builds shipping the mt76 wireless driver stack with mt7925 support. Upstream maintainers resolved the defect by adding an explicit NULL check on the returned capability pointer before use.
Critical Impact
A NULL-pointer dereference in kernel Wi-Fi handling can crash the kernel, leading to denial of service on affected wireless clients.
Affected Products
- Linux kernel builds containing the mt76 driver with mt7925 chipset support
- Distributions shipping vulnerable stable kernels prior to the fix commits
- Devices using MediaTek MT7925 Wi-Fi hardware
Discovery Timeline
- 2026-08-12 - CVE-2026-68439 published to NVD
- 2026-08-12 - Last updated in NVD database
Technical Details for CVE-2026-68439
Vulnerability Analysis
The defect lives in the mt7925_mcu_bss_he_tlv() routine inside the MediaTek mt7925 Wi-Fi driver. This function assembles High Efficiency (HE, Wi-Fi 6) TLV structures for a Basic Service Set (BSS) configuration message sent to the device microcontroller. To populate HE PHY capability fields, the routine calls mt76_connac_get_he_phy_cap() and immediately dereferences the returned pointer.
The helper mt76_connac_get_he_phy_cap() can return NULL when the requested capability structure is not present for the current band or interface configuration. The original code did not validate the return value, so any code path that produced a NULL result caused an in-kernel NULL pointer dereference during BSS setup. The fix introduces an explicit NULL check on cap before any field access.
Root Cause
The root cause is missing input validation on a pointer returned from an internal helper. This is a classic NULL pointer dereference pattern in kernel driver code, where an optional or conditionally populated capability lookup is treated as if it always succeeds.
Attack Vector
Triggering the flaw requires the driver to execute the BSS HE TLV construction path under a state where mt76_connac_get_he_phy_cap() returns NULL. Because the fault path lies in wireless connection management, adverse network conditions or crafted management frames that influence band or capability negotiation could reach the vulnerable code. The observable effect is a kernel oops and denial of service on the affected host.
No verified public exploit or proof-of-concept is available. Refer to the upstream commits for technical details: Kernel Commit 313343ab, Kernel Commit 42288cca, Kernel Commit 856f1588, and Kernel Commit 8d1b6738.
Detection Methods for CVE-2026-68439
Indicators of Compromise
- Kernel oops or panic messages referencing mt7925_mcu_bss_he_tlv or mt76_connac_get_he_phy_cap in dmesg or /var/log/kern.log.
- Unexpected wireless interface resets or driver reloads on hosts using MediaTek MT7925 hardware.
- Repeated NULL pointer dereference fault traces originating in the mt76 module.
Detection Strategies
- Correlate kernel crash telemetry with the loaded mt7925 and mt76 module versions to confirm exposure.
- Compare running kernel versions against distribution advisories referencing the listed stable commits.
- Monitor for wireless subsystem restart events that coincide with BSS association attempts.
Monitoring Recommendations
- Forward kernel logs and dmesg output to a centralized logging platform for pattern matching on mt76 faults.
- Track kernel package versions across the fleet to identify hosts still running pre-patch kernels.
- Alert on repeated Wi-Fi disconnects on MT7925-equipped devices, which may indicate the fault path is being reached.
How to Mitigate CVE-2026-68439
Immediate Actions Required
- Upgrade to a Linux kernel release that includes the upstream fix commits 313343ab, 42288cca, 856f1588, or 8d1b6738.
- Apply distribution vendor kernel updates as soon as they become available for your affected release branch.
- Inventory endpoints and embedded systems using MediaTek MT7925 Wi-Fi to prioritize patch deployment.
Patch Information
The fix adds a NULL check on the pointer returned by mt76_connac_get_he_phy_cap() before it is dereferenced in mt7925_mcu_bss_he_tlv(). The change has been backported to multiple stable branches via the commits linked above. Update to any kernel build that includes one of these commits for your branch.
Workarounds
- Unload the mt7925e or mt7925u module and disable the affected wireless interface if patching cannot be performed immediately.
- Use an alternative wired or USB network adapter on impacted hosts until a fixed kernel is deployed.
- Restrict exposure to untrusted wireless networks that could influence HE capability negotiation on unpatched systems.
# Verify running kernel and mt76 module version, then plan an update
uname -r
modinfo mt7925e | grep -E 'version|srcversion'
# Temporary mitigation: unload the vulnerable driver
sudo modprobe -r mt7925e
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
