CVE-2026-20423: Mediatek NbIoT SDK Privilege Escalation

CVE-2026-20423 Overview

CVE-2026-20423 is an out-of-bounds write vulnerability affecting MediaTek WLAN STA (Station) drivers. The vulnerability stems from a missing bounds check in the wireless LAN driver, which enables attackers to write data beyond the intended memory boundaries. Successful exploitation allows local escalation of privilege with User execution privileges, without requiring any user interaction.

This vulnerability impacts a range of MediaTek wireless chipsets commonly found in laptops, tablets, and embedded devices. The flaw is tracked internally by MediaTek under Patch ID WCNCR00465314 and Issue ID MSV-4956.

Critical Impact

Local attackers with user-level access can exploit this out-of-bounds write vulnerability to escalate privileges to higher system levels, potentially gaining full control over affected devices running vulnerable MediaTek wireless drivers.

Affected Products

• MediaTek NB-IoT SDK
• MediaTek MT7902
• MediaTek MT7920
• MediaTek MT7921
• MediaTek MT7922
• MediaTek MT7925
• MediaTek MT7927

Discovery Timeline

• 2026-03-02 - CVE-2026-20423 published to NVD
• 2026-03-03 - Last updated in NVD database

Technical Details for CVE-2026-20423

Vulnerability Analysis

This vulnerability is classified under CWE-787 (Out-of-bounds Write) and CWE-749 (Exposed Dangerous Method or Function). The flaw exists within the WLAN STA driver implementation across multiple MediaTek wireless chipsets. The driver fails to properly validate input boundaries before performing write operations, creating an opportunity for memory corruption.

The local attack vector requires an attacker to have user-level execution privileges on the target system. Once exploited, the vulnerability enables privilege escalation with high impact to confidentiality, integrity, and availability of the affected system. No user interaction is required for exploitation, making this vulnerability particularly dangerous in multi-user environments or systems where attackers may have limited initial access.

Root Cause

The root cause of CVE-2026-20423 is a missing bounds check in the MediaTek WLAN STA driver code. When processing certain wireless operations, the driver accepts input data without validating that the data length falls within expected boundaries. This oversight allows an attacker to supply malicious input that triggers a write operation beyond the allocated buffer, corrupting adjacent memory regions.

The CWE-749 classification indicates that a dangerous method or function is exposed without adequate protection, compounding the severity of the bounds checking failure.

Attack Vector

The attack is executed locally on the target system. An attacker with user-level privileges can interact with the WLAN STA driver through standard system interfaces or driver-specific calls. By crafting input that exploits the missing bounds validation, the attacker triggers an out-of-bounds write condition.

The memory corruption resulting from this write can be leveraged to overwrite critical data structures, function pointers, or security tokens, ultimately enabling privilege escalation from user to higher privilege levels such as root or kernel context.

Since no user interaction is needed, the attack can be automated and executed silently. Systems with the affected MediaTek wireless chipsets running vulnerable driver versions are susceptible when an attacker gains any level of local access.

Detection Methods for CVE-2026-20423

Indicators of Compromise

• Unexpected crashes or kernel panics in systems using MediaTek wireless drivers
• Abnormal privilege escalation events from user-level processes
• Unusual memory access patterns or segmentation faults related to WLAN driver operations
• System logs showing driver errors associated with mt79xx series chipsets

Detection Strategies

• Monitor system logs for driver-related crashes or memory corruption indicators in MediaTek WLAN components
• Implement endpoint detection rules to alert on privilege escalation patterns from standard user contexts
• Use kernel integrity monitoring to detect unauthorized modifications to driver memory regions
• Deploy behavioral analysis to identify processes attempting to manipulate WLAN driver interfaces abnormally

Monitoring Recommendations

• Enable verbose logging for wireless driver operations on systems with affected MediaTek chipsets
• Configure SIEM rules to correlate driver errors with subsequent privilege escalation events
• Establish baseline behavior for WLAN driver interactions and alert on deviations
• Implement file integrity monitoring on driver binaries and associated configuration files

How to Mitigate CVE-2026-20423

Immediate Actions Required

• Apply the latest firmware and driver updates from MediaTek addressing Patch ID WCNCR00465314
• Restrict local access to systems with affected MediaTek wireless chipsets to trusted users only
• Review and audit user accounts with local system access on devices running vulnerable configurations
• Consider disabling or limiting wireless functionality on critical systems until patches are applied

Patch Information

MediaTek has released a security patch addressing this vulnerability. The fix is documented in the MediaTek Security Bulletin for March 2026. Administrators should obtain updated drivers from device manufacturers (OEMs) who integrate MediaTek wireless chipsets, as patches are typically distributed through OEM channels.

The patch addresses the missing bounds check by implementing proper input validation before write operations in the affected driver code paths.

Workarounds

• Limit local user access on systems with affected MediaTek wireless hardware to reduce attack surface
• Implement application whitelisting to prevent unauthorized programs from interacting with driver interfaces
• Use least-privilege principles to minimize the impact of potential privilege escalation
• Consider switching to wired network connections on critical systems until driver updates are deployed

# Check for MediaTek wireless chipsets on Linux systems
lspci -nn | grep -i mediatek

# Verify current wireless driver version
modinfo mt7921e 2>/dev/null | grep -E "^(filename|version|description):"

# Temporarily disable MediaTek wireless interface if needed
sudo ip link set wlan0 down