CVE-2026-20401 is a security vulnerability identified in multiple MediaTek modem chipsets, including models MT2735 through MT8797, specifically affecting the Modem NR15 version. The vulnerability is classified under CWE-617 (Reachable Assertion), indicating that an assertion in the modem firmware can be triggered unexpectedly, leading to an uncaught exception and subsequent system crash. This crash results in a denial of service condition on the affected device. The attack vector involves a user equipment (UE) device connecting to a rogue base station controlled by an attacker. Because the vulnerability requires no additional execution privileges and no user interaction, it can be exploited remotely and silently. The rogue base station can send crafted signals or messages that trigger the assertion failure in the modem firmware. The impact is primarily on availability, as the device may crash or reboot, disrupting normal operations. The vulnerability affects a broad range of MediaTek modem chipsets widely used in smartphones, IoT devices, and embedded systems. No CVSS score has been assigned yet, and no public exploits have been reported. The vendor has acknowledged the issue and assigned a patch ID (MOLY01738310) and issue ID (MSV-5933), indicating that a fix is planned or available. The vulnerability's technical root cause is an assertion that does not properly handle unexpected conditions, leading to an uncaught exception and system instability. This type of flaw can be exploited by attackers setting up rogue base stations to target devices in their vicinity, potentially causing widespread service interruptions.

For European organizations, the primary impact of CVE-2026-20401 is on the availability of devices using the affected MediaTek modem chipsets. Telecom operators, mobile network providers, and enterprises relying on mobile connectivity for critical communications could experience service disruptions if devices crash or reboot unexpectedly. This could affect mobile workforce productivity, IoT deployments, and critical infrastructure monitoring systems that depend on stable cellular connections. The vulnerability could be leveraged by attackers to conduct targeted denial of service attacks in specific geographic areas by deploying rogue base stations, potentially disrupting emergency services, financial transactions, or industrial control systems. The lack of required user interaction and low privilege requirements increase the risk of widespread exploitation, especially in densely populated urban areas with high mobile device usage. Although no known exploits are currently in the wild, the potential for disruption in sectors such as telecommunications, transportation, healthcare, and public safety is significant. Organizations may also face reputational damage and regulatory scrutiny if service outages occur due to this vulnerability.

1. Apply vendor patches promptly once available (Patch ID: MOLY01738310) to address the assertion failure in the modem firmware. 2. Telecom operators should enhance detection and mitigation capabilities for rogue base stations, including deploying network monitoring tools that identify anomalous base station behavior. 3. Implement network access controls and anomaly detection on mobile networks to prevent unauthorized base station connections. 4. For critical IoT deployments using affected MediaTek chipsets, consider network segmentation and fallback communication methods to maintain availability during attacks. 5. Educate security teams and incident responders about the signs of rogue base station attacks and establish response protocols. 6. Collaborate with device manufacturers and mobile network providers to ensure timely updates and coordinated vulnerability disclosure. 7. Monitor threat intelligence feeds for emerging exploit techniques targeting this vulnerability. 8. Where possible, restrict device connectivity to trusted networks and disable automatic connections to unknown base stations. 9. Conduct regular security assessments of mobile infrastructure to identify and remediate potential attack vectors related to rogue base stations.