CVE-2026-20404 is a vulnerability classified as CWE-787 (out-of-bounds write) found in the modem firmware of a wide range of MediaTek chipsets, including MT2735 through MT8893 series. The root cause is improper input validation within the modem's handling of network communications, which can be triggered when a User Equipment (UE) device connects to a maliciously controlled rogue base station. This triggers an out-of-bounds write in memory, leading to a system crash and resulting in a denial of service (DoS) condition. The vulnerability does not require any privileges or user interaction, making it easier to exploit in scenarios where attackers can set up rogue base stations to intercept or manipulate UE connections. The affected modem versions include NR15, NR16, NR17, and NR17R. The CVSS v3.1 score is 6.5 (medium severity) with an attack vector of adjacent network (AV:A), low attack complexity (AC:L), no privileges required (PR:N), no user interaction (UI:N), and impact limited to availability (A:H) without affecting confidentiality or integrity. Although no known exploits are currently reported in the wild, the potential for remote DoS attacks exists, which could disrupt mobile communications. MediaTek has assigned a patch ID (MOLY01689248) to address this issue, though no direct patch links are provided. The vulnerability highlights risks in cellular modem firmware where rogue base stations can be leveraged to degrade service availability.

For European organizations, the primary impact of CVE-2026-20404 is the potential for remote denial of service on devices using the affected MediaTek modems. This could disrupt mobile communications for end-users, impacting business operations reliant on cellular connectivity, such as remote work, IoT deployments, and critical communications. Telecom operators could face network reliability issues if rogue base stations are deployed by malicious actors within their coverage areas. The lack of confidentiality or integrity impact limits data breach risks, but availability degradation can cause operational downtime and customer dissatisfaction. Organizations in sectors like finance, healthcare, and public services that depend on mobile networks for critical functions may experience service interruptions. The vulnerability also raises concerns about the security of cellular infrastructure against rogue base station attacks, which have been historically used for surveillance or disruption. Given the widespread use of MediaTek chipsets in consumer and industrial devices, the scope of affected systems is broad, increasing the potential scale of impact across Europe.

1. Apply the official firmware patches from MediaTek (Patch ID: MOLY01689248) as soon as they become available to ensure the vulnerability is remediated. 2. Network operators should enhance detection and mitigation capabilities for rogue base stations using radio frequency monitoring tools and anomaly detection systems. 3. Implement network-level protections such as mutual authentication and encryption enhancements to reduce the risk of rogue base station exploitation. 4. For enterprise and critical infrastructure, consider deploying mobile threat defense solutions that can detect suspicious cellular network behavior. 5. Educate users and administrators about the risks of connecting to untrusted cellular networks and encourage the use of VPNs or secure communication channels when possible. 6. Collaborate with device manufacturers and telecom providers to ensure timely updates and security patches are distributed and installed. 7. Monitor security advisories from MediaTek and related vendors for updates or new exploit information. 8. Conduct regular security assessments of mobile device fleets to verify patch levels and detect anomalies.