CVE-2025-20685: Mediatek SDK RCE Vulnerability

CVE-2025-20685 Overview

CVE-2025-20685 is a heap-based out-of-bounds write vulnerability [CWE-122] in the MediaTek wireless LAN access point (WLAN AP) driver. The flaw stems from an incorrect bounds check, allowing an attacker on an adjacent network to write outside an allocated buffer. Successful exploitation enables remote code execution on the affected access point with no user interaction and no additional privileges. MediaTek tracks the issue as MSV-3409 and addresses it with patch ID WCNCR00416226. Affected chipsets include the MT6890, MT7915, MT7916, MT7981, and MT7986, which ship in numerous consumer and enterprise wireless products, including OpenWrt-based devices.

Critical Impact
An unauthenticated attacker within wireless range can execute arbitrary code on the access point, gaining a network foothold capable of intercepting or redirecting all WLAN traffic.

Affected Products

MediaTek Software Development Kit (chipsets MT6890, MT7915, MT7916, MT7981, MT7986)
OpenWrt 19.07.0 and 21.02.0 builds using the affected MediaTek WLAN driver
MediaTek-powered wireless access points and routers running the unpatched AP driver

Discovery Timeline

2025-07-08 - CVE-2025-20685 published to NVD
2025-07 - MediaTek releases July 2025 Product Security Bulletin with patch WCNCR00416226
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-20685

Vulnerability Analysis

The vulnerability lives in the MediaTek WLAN AP driver code path that processes incoming 802.11 management or control frames. An incorrect bounds check permits a write past the end of a heap buffer, classifying the defect as an out-of-bounds write [CWE-122]. Because the affected component is a kernel-mode wireless driver, memory corruption translates directly into kernel-context code execution on the access point.

Exploitation requires only adjacency to the radio interface. The attack vector is Adjacent Network, attack complexity is Low, no privileges are needed, and no user interaction is required. Confidentiality, integrity, and availability impacts are all rated High. EPSS currently estimates exploitation probability at 0.296%.

Root Cause

The driver performs a size or index validation that does not accurately reflect the bounds of the destination buffer. When attacker-controlled length or offset values from a wireless frame are accepted by the flawed check, the subsequent memory copy writes beyond the allocated heap region. This corrupts adjacent kernel structures and allocator metadata, providing an exploit primitive for hijacking control flow within the WLAN driver.

Attack Vector

An attacker positions a station within radio range of the vulnerable access point and transmits a crafted 802.11 frame. The malformed frame triggers the flawed code path inside the AP driver, producing the out-of-bounds write. Reliable exploitation yields code execution in the AP's kernel context, after which the attacker can pivot into the wired network, install persistent backdoors, or downgrade encryption to surveil clients.

No public proof-of-concept exploit is currently available, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog. Technical specifics are intentionally limited in the MediaTek advisory. Refer to the MediaTek Product Security Bulletin July 2025 for vendor guidance.

Detection Methods for CVE-2025-20685

Indicators of Compromise

Unexpected reboots, kernel oops messages, or watchdog resets on MediaTek-based access points running unpatched firmware.
New or modified processes on the AP, particularly listeners on non-standard ports or outbound connections from the device's management interface.
Anomalous 802.11 management frames with malformed information elements observed via wireless intrusion detection sensors.
Configuration changes on the AP that were not initiated by administrators, including altered DNS, routing, or firewall rules.

Detection Strategies

Deploy a wireless intrusion detection system (WIDS) capable of flagging malformed 802.11 frames and protocol anomalies near vulnerable access points.
Inventory firmware versions across all MediaTek-based APs and OpenWrt devices, and flag any using the affected MT6890, MT7915, MT7916, MT7981, or MT7986 drivers without patch WCNCR00416226.
Compare baseline AP configuration and running services against current state to identify unauthorized post-exploitation changes.

Monitoring Recommendations

Forward AP syslog, dmesg, and authentication logs to a centralized SIEM for correlation against client connection events.
Monitor egress from access-point management VLANs for outbound traffic that should not originate from infrastructure devices.
Track DHCP, ARP, and DNS anomalies on segments served by MediaTek APs to identify rogue activity following compromise.

How to Mitigate CVE-2025-20685

Immediate Actions Required

Apply firmware updates from device vendors that incorporate MediaTek patch WCNCR00416226 as soon as they are available.
Identify all MediaTek MT6890, MT7915, MT7916, MT7981, and MT7986 access points and OpenWrt 19.07.0 and 21.02.0 deployments in the environment.
Place vulnerable APs on isolated management VLANs with strict egress filtering until patched.
Subscribe to MediaTek and downstream OEM security bulletins to track patch availability across device fleets.

Patch Information

MediaTek published the fix in its July 2025 Product Security Bulletin under patch ID WCNCR00416226 and issue ID MSV-3409. Because MediaTek distributes fixes through OEMs, end users must obtain firmware images from their specific access point or router vendor. OpenWrt users should track the MediaTek Product Security Bulletin July 2025 and upstream OpenWrt advisories for backported builds.

Workarounds

Reduce wireless transmit power and shorten radio coverage to limit the area from which an adjacent attacker can reach the AP.
Disable guest SSIDs and unused radios on vulnerable devices to shrink the exposed attack surface.
Segment access points behind a wired firewall enforcing least-privilege rules between the AP management network and corporate or client networks.
Replace end-of-life devices that will not receive a vendor patch with hardware that has current security support.

bash

# Example: verify MediaTek WLAN driver version on an OpenWrt device
opkg list-installed | grep -E 'mt7915|mt7916|mt7981|mt7986|mt6890'
logread | grep -i 'mt76\|mtk_wifi'
# After updating, confirm the firmware build includes patch WCNCR00416226
cat /etc/openwrt_release