CVE-2026-20401 is a vulnerability classified under CWE-617 (Reachable Assertion) found in the modem component of various MediaTek chipsets, including models MT2735 through MT8797. The flaw arises from an uncaught exception triggered by a reachable assertion failure within the modem firmware. When a user equipment (UE) device connects to a maliciously controlled rogue base station, the attacker can remotely induce a system crash, resulting in a denial of service condition. This attack vector requires no user interaction and no elevated privileges, making it relatively easy to exploit in scenarios where an attacker can simulate or control a base station environment. The vulnerability impacts the availability of the device but does not compromise confidentiality or integrity. The CVSS v3.1 base score is 6.5, reflecting medium severity with attack vector as adjacent network, low attack complexity, no privileges required, and no user interaction. The vulnerability affects a wide range of MediaTek chipsets widely deployed in smartphones and IoT devices. Although no exploits have been reported in the wild, the presence of a patch (MOLY01738310) indicates that vendors and users should apply updates promptly to mitigate risk. The issue was reserved in November 2025 and published in February 2026, indicating recent discovery and disclosure.

The primary impact of CVE-2026-20401 is a remote denial of service on devices using affected MediaTek chipsets. This can disrupt mobile device availability, potentially affecting communication, data access, and critical services relying on mobile connectivity. In environments where devices are used for essential operations—such as emergency services, industrial IoT, or enterprise mobile deployments—a DoS could lead to operational downtime and safety risks. The attack requires proximity or control over a rogue base station, which may limit large-scale exploitation but poses a significant threat in targeted attacks or hostile environments. The vulnerability does not allow privilege escalation or data compromise, limiting its impact to availability. However, the widespread use of MediaTek chipsets in consumer and industrial devices globally means a large attack surface. Organizations with mobile fleets, IoT deployments, or critical infrastructure using these chipsets may face service interruptions and reputational damage if exploited.

To mitigate CVE-2026-20401, organizations and users should promptly apply the official patch MOLY01738310 provided by MediaTek or device manufacturers. Network operators and security teams should monitor for rogue base stations or suspicious signaling activity indicative of man-in-the-middle attacks targeting mobile devices. Deploying base station authentication and detection mechanisms can reduce the risk of devices connecting to malicious infrastructure. Device manufacturers should ensure firmware updates are delivered securely and efficiently to end users. For high-risk environments, consider network segmentation and restricting device connectivity to trusted networks. Security teams should also educate users about the risks of connecting to unknown or untrusted cellular networks, although user interaction is not required for exploitation. Continuous monitoring of device behavior and anomaly detection can help identify potential exploitation attempts.