CVE-2026-20419: Mediatek Nbiot Sdk DoS Vulnerability

CVE-2026-20419 Overview

CVE-2026-20419 is a denial of service vulnerability in MediaTek WLAN AP/STA firmware caused by an uncaught exception that can render affected systems unresponsive. This firmware-level vulnerability affects a wide range of MediaTek wireless chipsets and associated software development kits, including products used in routers, IoT devices, and consumer electronics running OpenWrt.

The vulnerability allows an adjacent network attacker to remotely trigger a denial of service condition without requiring any user interaction or elevated privileges. When exploited, the uncaught exception causes the wireless subsystem to become irresponsive, effectively disabling network connectivity for affected devices.

Critical Impact

Adjacent network attackers can render wireless connectivity inoperable on affected MediaTek-based devices without authentication or user interaction, impacting availability for routers, IoT devices, and consumer electronics.

Affected Products

• MediaTek NB-IoT SDK
• MediaTek Software Development Kit
• MediaTek MT7915, MT7916, MT7920, MT7921, MT7922, MT7925, MT7927 (WiFi 6/6E chipsets)
• MediaTek MT7981, MT7986, MT7902 (Router/AP chipsets)
• MediaTek MT8668, MT8676, MT8678, MT8775, MT8791T, MT8792, MT8793, MT8796 (Smart device chipsets)
• MediaTek MT8873, MT8883, MT8893, MT8910, MT8196 (Consumer electronics chipsets)
• MediaTek MT6890, MT6989TB (Mobile platform chipsets)
• OpenWrt 19.07.0 and 21.02.0

Discovery Timeline

• February 2, 2026 - CVE-2026-20419 published to NVD
• February 5, 2026 - Last updated in NVD database

Technical Details for CVE-2026-20419

Vulnerability Analysis

This vulnerability (CWE-754: Improper Check for Unusual or Exceptional Conditions) resides in the wireless LAN firmware that operates in both Access Point (AP) and Station (STA) modes on MediaTek chipsets. The firmware fails to properly handle an exceptional condition, resulting in an uncaught exception that propagates through the system and causes the device to become unresponsive.

The attack can be executed from an adjacent network position, meaning an attacker must be within wireless range or on the same network segment as the target device. No authentication is required, and the attack succeeds without any user interaction, making it particularly concerning for deployed infrastructure like routers and IoT gateways.

MediaTek has assigned Patch IDs WCNCR00461663 and WCNCR00463309 to address this issue, tracked internally as Issue ID MSV-4852.

Root Cause

The root cause is an improper check for unusual or exceptional conditions (CWE-754) in the WLAN firmware exception handling logic. The firmware does not adequately validate or catch certain exceptional states that can occur during wireless communication, allowing malformed or specially crafted wireless traffic to trigger an unhandled exception. This causes the firmware to enter a fault state from which it cannot recover without a device restart.

Attack Vector

The attack vector is through adjacent network access, requiring the attacker to be within wireless range of the target device or on the same local network segment. The attacker can send specially crafted wireless frames or traffic that triggers the uncaught exception in the WLAN firmware. The attack requires no privileges and no user interaction, making automated exploitation feasible.

The vulnerability affects both AP mode (when the device is acting as a wireless access point) and STA mode (when the device is connecting as a client), broadening the potential attack surface across different deployment scenarios.

Detection Methods for CVE-2026-20419

Indicators of Compromise

• Sudden loss of wireless connectivity without corresponding hardware failure
• Devices becoming unresponsive and requiring manual reboot to restore wireless functionality
• Repeated wireless subsystem crashes in system logs
• Anomalous wireless traffic patterns originating from adjacent network segments

Detection Strategies

• Monitor for unusual wireless frame patterns that may indicate exploitation attempts
• Implement network monitoring to detect devices that repeatedly lose wireless connectivity
• Review firmware logs for uncaught exception errors or WLAN subsystem crashes
• Deploy wireless intrusion detection systems (WIDS) to identify malicious wireless traffic

Monitoring Recommendations

• Enable verbose logging on MediaTek-based devices where supported to capture firmware exception events
• Implement alerting for unexpected device reboots or wireless subsystem restarts
• Monitor network availability metrics for MediaTek-powered infrastructure devices
• Track firmware crash events across device fleets to identify potential exploitation campaigns

How to Mitigate CVE-2026-20419

Immediate Actions Required

• Review the MediaTek Security Bulletin February 2026 for patch availability
• Identify all MediaTek-based devices in your environment using affected chipsets
• Prioritize patching for devices exposed to untrusted adjacent networks
• Consider network segmentation to limit adjacent network access to critical devices

Patch Information

MediaTek has released patches addressing this vulnerability as documented in their February 2026 security bulletin. The patches are identified by Patch IDs WCNCR00461663 and WCNCR00463309. Organizations should obtain firmware updates through their device manufacturers or the official MediaTek SDK channels.

For OpenWrt deployments, users should monitor the OpenWrt security advisories for updated packages that incorporate the MediaTek firmware fixes. Firmware updates should be applied following vendor recommendations and tested in non-production environments where possible.

Workarounds

• Restrict adjacent network access to affected devices through network segmentation and access controls
• Implement wireless intrusion prevention systems to filter potentially malicious wireless traffic
• Where feasible, disable unused wireless interfaces (AP or STA mode) to reduce attack surface
• Monitor device availability and implement automated alerting for unresponsive systems