CVE-2026-20456 Overview
CVE-2026-20456 is a denial-of-service vulnerability in the MediaTek wireless LAN (WLAN) station (STA) driver. A missing bounds check allows a local attacker with low-privilege user execution rights to trigger a system crash without user interaction. The flaw is classified as an out-of-bounds write [CWE-787] and is tracked by MediaTek as Patch ID WCNCR00480851 and Issue ID MSV-6338. The vulnerability affects multiple MediaTek Wi-Fi chipset firmware versions, including the MT7902, MT7920, MT7921, MT7922, MT7925, and MT7927 series. MediaTek addressed the issue in the MediaTek Product Security Bulletin – June 2026.
Critical Impact
A local user can crash affected systems by exploiting the WLAN STA driver, resulting in denial of service against availability of the wireless subsystem and host device.
Affected Products
- MediaTek MT7902 / MT7920 / MT7921 firmware
- MediaTek MT7922 / MT7925 / MT7927 firmware
- Devices integrating the listed MediaTek WLAN chipsets
Discovery Timeline
- 2026-06-01 - CVE-2026-20456 published to NVD
- 2026-06-01 - MediaTek releases security bulletin and patch WCNCR00480851
- 2026-06-01 - Last updated in NVD database
Technical Details for CVE-2026-20456
Vulnerability Analysis
The vulnerability resides in the MediaTek WLAN STA driver, which handles wireless client-mode operations for affected chipsets. The driver fails to perform a required bounds check before writing data, leading to an out-of-bounds write condition. When the unchecked write occurs, the driver corrupts adjacent memory in kernel context, causing the affected system to crash.
Exploitation is constrained to local attack vectors. An attacker needs the ability to execute code on the device with standard user privileges. No user interaction is required, and the impact is limited to availability — the bug does not directly disclose information or allow privilege escalation. The denial-of-service outcome affects the host operating system, not only the wireless subsystem.
Root Cause
The root cause is a missing bounds validation on input handled by the WLAN STA driver. The driver writes to a buffer using an attacker-influenced length or index without verifying that the operation stays within allocated memory. This pattern aligns with [CWE-787: Out-of-bounds Write] and is a recurring class of defect in wireless driver stacks where untrusted frame or command data flows into fixed-size kernel buffers.
Attack Vector
A local, low-privileged user invokes the vulnerable code path in the WLAN STA driver, supplying input that bypasses the missing bounds check. The resulting out-of-bounds write corrupts kernel memory and crashes the system. No verified public proof-of-concept exists, and MediaTek has not published exploit technical details. Refer to the MediaTek Security Bulletin – June 2026 for vendor-supplied technical context.
Detection Methods for CVE-2026-20456
Indicators of Compromise
- Unexpected kernel panics or system reboots correlated with WLAN driver stack traces referencing the MediaTek STA driver.
- Crash dumps citing functions in the MediaTek WLAN kernel module on devices using MT79xx chipsets.
- Repeated WLAN subsystem restarts on a host preceding a full system crash.
Detection Strategies
- Monitor kernel logs (dmesg, journalctl, Windows Event Log) for driver fault signatures involving MediaTek WLAN modules.
- Correlate device crash telemetry with the firmware build version reported by the affected MT79xx chipset.
- Inventory endpoints to identify hosts running pre-patch MediaTek WLAN firmware listed in the June 2026 bulletin.
Monitoring Recommendations
- Forward endpoint kernel crash and driver fault events to a centralized log platform for correlation across the fleet.
- Track firmware and driver version compliance against the MediaTek June 2026 bulletin baseline.
- Alert on repeated WLAN driver reset events that may indicate exploitation attempts or instability.
How to Mitigate CVE-2026-20456
Immediate Actions Required
- Apply the MediaTek patch WCNCR00480851 through the device OEM update channel.
- Identify all endpoints, mobile devices, and embedded systems using affected MT7902, MT7920, MT7921, MT7922, MT7925, or MT7927 chipsets.
- Restrict local code execution privileges on shared or multi-user systems until patches are deployed.
Patch Information
MediaTek issued the fix in the June 2026 Product Security Bulletin under Patch ID WCNCR00480851 and Issue ID MSV-6338. OEMs integrating MediaTek chipsets must incorporate the patched driver and firmware into their device updates. Consult the MediaTek Product Security Bulletin – June 2026 for the authoritative patched versions.
Workarounds
- Limit local account access on systems that cannot receive the patch immediately.
- Disable the WLAN interface on devices that do not require wireless connectivity until firmware updates are applied.
- Enforce application allowlisting to reduce the risk of untrusted local code interacting with the vulnerable driver.
# Verify whether an affected MediaTek WLAN module is loaded (Linux example)
lsmod | grep -Ei 'mt79|mt7902|mt7920|mt7921|mt7922|mt7925|mt7927'
# Temporarily disable the wireless interface until patching is complete
sudo ip link set dev wlan0 down
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
