CVE-2026-20430: Mediatek SDK Privilege Escalation Flaw

CVE-2026-20430 Overview

CVE-2026-20430 is an out-of-bounds write vulnerability in MediaTek's WLAN Access Point (AP) firmware that affects multiple MediaTek chipsets and OpenWrt distributions. The vulnerability stems from an incorrect bounds check in the wireless LAN firmware, which could allow an attacker within adjacent network range to trigger a memory corruption condition. This firmware-level flaw enables remote privilege escalation without requiring user interaction or additional execution privileges.

Critical Impact

Adjacent network attackers can achieve privilege escalation on affected MediaTek wireless chipsets and OpenWrt installations without user interaction, potentially gaining full control over the wireless access point infrastructure.

Affected Products

• MediaTek Software Development Kit
• OpenWrt 19.07.0, 21.02.0, 23.05.0
• MediaTek MT6890 Chipset
• MediaTek MT7915 Chipset
• MediaTek MT7916 Chipset
• MediaTek MT7981 Chipset
• MediaTek MT7986 Chipset

Discovery Timeline

• March 2, 2026 - CVE-2026-20430 published to NVD
• March 2, 2026 - Last updated in NVD database

Technical Details for CVE-2026-20430

Vulnerability Analysis

This vulnerability is classified as CWE-787 (Out-of-Bounds Write), a memory corruption flaw that occurs when the WLAN AP firmware writes data past the boundaries of allocated memory buffers. The incorrect bounds check in the firmware fails to properly validate input lengths or array indices before writing data, allowing an attacker to corrupt adjacent memory regions.

The attack can be conducted from an adjacent network position, meaning the attacker must be within wireless range or on the same local network segment as the vulnerable access point. No authentication or special privileges are required to exploit this vulnerability, and no user interaction is necessary, making it particularly dangerous in enterprise and public WiFi deployments.

Successful exploitation could lead to arbitrary code execution within the firmware context, potentially allowing attackers to compromise the wireless access point, intercept network traffic, pivot to connected devices, or establish persistent access to the network infrastructure.

Root Cause

The root cause of CVE-2026-20430 is an incorrect bounds check implementation in the MediaTek WLAN AP firmware. When processing certain wireless frames or management data, the firmware fails to properly validate that data lengths or indices are within acceptable ranges before performing write operations. This insufficient validation allows crafted input to write beyond allocated buffer boundaries, corrupting critical firmware data structures or control flow information.

Attack Vector

The attack vector for this vulnerability is Adjacent Network (AV:A), requiring the attacker to have access to the local network segment or be within wireless range of the affected access point. The attack complexity is low, as exploitation does not require special conditions or complex attack chains.

An attacker could exploit this vulnerability by:

1. Positioning themselves within wireless range of a vulnerable MediaTek-based access point
2. Crafting malicious wireless frames that trigger the incorrect bounds check
3. Sending the malicious frames to the target access point
4. Achieving out-of-bounds memory write that corrupts firmware execution state
5. Gaining elevated privileges within the wireless firmware context

The vulnerability requires no privileges on the target system and no user interaction, making it exploitable in automated attack scenarios. The impact spans confidentiality, integrity, and availability, as successful exploitation could allow full compromise of the access point.

Detection Methods for CVE-2026-20430

Indicators of Compromise

• Unexpected access point reboots or firmware crashes that may indicate exploitation attempts
• Anomalous wireless traffic patterns or malformed 802.11 frames targeting the access point
• Unexplained configuration changes on MediaTek-based wireless devices
• Evidence of unauthorized firmware modifications or backdoor installations

Detection Strategies

• Deploy wireless intrusion detection systems (WIDS) to monitor for malformed or suspicious 802.11 frames
• Implement network monitoring to detect unusual traffic patterns targeting access point management interfaces
• Monitor system logs on OpenWrt devices for firmware exceptions, kernel panics, or unexpected restarts
• Conduct regular firmware integrity verification on affected MediaTek chipset devices

Monitoring Recommendations

• Enable verbose logging on affected access points to capture potential exploitation indicators
• Configure alerting for access point firmware crashes or unexpected reboots
• Implement network segmentation to limit adjacent network attack surface
• Deploy SentinelOne Singularity for network infrastructure monitoring where supported

How to Mitigate CVE-2026-20430

Immediate Actions Required

• Apply firmware updates from MediaTek and OpenWrt as soon as they become available
• Review network architecture to ensure proper segmentation between wireless access points and critical infrastructure
• Limit physical wireless coverage to reduce the attack surface from adjacent network positions
• Monitor affected devices closely for signs of compromise until patches are applied

Patch Information

MediaTek has released security patches to address this vulnerability. The patch is identified by Patch ID: WCNCR00467553 and Issue ID: MSV-5151. Organizations should consult the MediaTek Security Bulletin for March 2026 for detailed patching instructions and firmware update availability.

For OpenWrt installations, users should monitor the OpenWrt security advisories and upgrade to patched versions when available. The affected OpenWrt versions include 19.07.0, 21.02.0, and 23.05.0.

Workarounds

• Implement network access controls to restrict which devices can communicate with access point management interfaces
• Enable MAC filtering and strong wireless authentication (WPA3 where supported) to limit adjacent network access
• Deploy additional network monitoring to detect exploitation attempts while awaiting patches
• Consider temporarily disabling affected access points in high-security environments if patches are unavailable

# OpenWrt configuration example - enable additional logging
uci set system.@system[0].log_size='512'
uci set system.@system[0].log_proto='udp'
uci set system.@system[0].log_ip='<syslog-server-ip>'
uci commit system
/etc/init.d/log restart

# Restrict management interface access
uci set uhttpd.main.listen_http='127.0.0.1:80'
uci set uhttpd.main.listen_https='127.0.0.1:443'
uci commit uhttpd
/etc/init.d/uhttpd restart