CVE-2026-20408 Overview
A heap buffer overflow vulnerability exists in the WLAN component of MediaTek chipsets and the MediaTek Software Development Kit. This out-of-bounds write vulnerability can be exploited by an attacker within adjacent network proximity to achieve privilege escalation without requiring any user interaction or additional execution privileges. The vulnerability affects multiple MediaTek wireless chipsets commonly found in routers, access points, and IoT devices running OpenWrt firmware.
Critical Impact
Remote (proximal/adjacent) escalation of privilege with no user interaction required. Attackers on the same network segment can exploit this heap buffer overflow to gain elevated privileges on vulnerable MediaTek WLAN devices.
Affected Products
- MediaTek Software Development Kit
- OpenWrt 19.07.0, 21.02.0, and 23.05.0
- MediaTek MT6890
- MediaTek MT7615
- MediaTek MT7915
- MediaTek MT7916
- MediaTek MT7981
- MediaTek MT7986
Discovery Timeline
- February 2, 2026 - CVE-2026-20408 published to NVD
- February 4, 2026 - Last updated in NVD database
Technical Details for CVE-2026-20408
Vulnerability Analysis
This vulnerability is classified as CWE-122 (Heap-based Buffer Overflow) and CWE-787 (Out-of-bounds Write). The flaw resides within the WLAN driver implementation for MediaTek wireless chipsets. When processing certain wireless frames or management data, the driver fails to properly validate input boundaries before writing data to a heap-allocated buffer. This allows an attacker to overflow the intended buffer boundaries and corrupt adjacent heap memory.
The adjacent network attack vector means that exploitation requires the attacker to be within wireless range or on the same network segment as the vulnerable device. No authentication or user interaction is required, making this particularly dangerous for wireless access points and routers deployed in shared environments.
Root Cause
The root cause is improper bounds checking in the WLAN driver's memory handling routines. When processing wireless data frames, the driver allocates a fixed-size heap buffer but does not adequately verify that incoming data fits within the allocated space. This allows specially crafted wireless packets to write beyond the buffer's boundaries, corrupting heap metadata and potentially adjacent memory structures.
Attack Vector
The attack vector is adjacent network (AV:A), meaning an attacker must be able to send network packets to the vulnerable device. For wireless devices, this typically means being within radio frequency range of the target. The attacker can send malicious 802.11 frames or management packets that trigger the vulnerable code path in the WLAN driver.
The exploitation does not require any privileges on the target system, nor does it require any interaction from users or administrators. Upon successful exploitation, the attacker can achieve privilege escalation on the affected device, potentially gaining full control over the wireless controller or the device itself.
The vulnerability is tracked internally by MediaTek as Patch ID: WCNCR00461651 and Issue ID: MSV-4758.
Detection Methods for CVE-2026-20408
Indicators of Compromise
- Unexpected crashes or reboots of wireless access points or routers using MediaTek chipsets
- Anomalous wireless management frames detected in network traffic captures
- Unusual memory allocation patterns or heap corruption errors in system logs
- Unauthorized configuration changes on wireless devices
Detection Strategies
- Monitor WLAN driver logs for buffer overflow errors or memory corruption indicators
- Deploy wireless intrusion detection systems (WIDS) to identify malformed 802.11 frames
- Implement network segmentation to limit adjacent network attack surface
- Use SentinelOne Singularity to detect anomalous behavior on managed endpoints communicating with affected access points
Monitoring Recommendations
- Enable verbose logging on MediaTek WLAN devices where available
- Monitor for unusual network traffic patterns targeting wireless infrastructure
- Implement alerting for firmware crashes or unexpected device reboots
- Track authentication events and privilege changes on network infrastructure devices
How to Mitigate CVE-2026-20408
Immediate Actions Required
- Apply the vendor-provided security patch immediately (Patch ID: WCNCR00461651)
- Review and update firmware on all devices using affected MediaTek chipsets
- Implement network segmentation to isolate wireless infrastructure from critical assets
- Enable wireless intrusion prevention features where available
Patch Information
MediaTek has released security updates addressing this vulnerability. Refer to the MediaTek Security Bulletin - February 2026 for detailed patch information and download instructions. For devices running OpenWrt, check for updated packages that incorporate the MediaTek driver fixes for versions 19.07.0, 21.02.0, and 23.05.0.
Workarounds
- Reduce wireless transmission power to limit attack range where operationally feasible
- Implement MAC address filtering as an additional layer of access control (note: this is not a complete mitigation)
- Deploy wireless intrusion prevention systems to detect and block malicious frames
- Consider replacing vulnerable devices with models using patched firmware if updates are not available
# Check OpenWrt package versions for MediaTek WLAN drivers
opkg list-installed | grep -i mt76
opkg list-installed | grep -i mediatek
# Update OpenWrt packages (after vendor patch release)
opkg update
opkg upgrade mt76-firmware
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
