CVE-2025-20757 identifies a reachable assertion vulnerability (CWE-617) in the modem firmware of numerous MediaTek chipsets, including MT2735, MT6833, MT6853, MT6855, MT6873, MT6875, MT6877, MT6880, MT6883, MT6885, MT6889, MT6890, MT6891, MT6893, MT8675, MT8771, MT8791, and MT8797. The vulnerability stems from improper input validation within the modem's handling of network signals, specifically when a user equipment (UE) connects to a base station. An attacker controlling a rogue base station can send crafted signals that trigger an assertion failure in the modem firmware, causing the system to crash and resulting in a denial of service condition. This can be exploited remotely without requiring user interaction or elevated privileges, increasing the attack surface significantly. The affected modem versions are identified as Modem NR15. The flaw was reserved in November 2024 and published in December 2025, with no CVSS score assigned yet. No public exploits have been reported, but the vulnerability’s characteristics suggest it could disrupt mobile communications and dependent services. The issue is tracked internally by MediaTek as MSV-4644 and patched under MOLY01673751, though patch availability and deployment status remain unspecified. The vulnerability impacts confidentiality minimally but poses a high risk to availability, particularly for devices relying on these modems for cellular connectivity.

For European organizations, the primary impact of CVE-2025-20757 is the potential for remote denial of service on devices using affected MediaTek modems. This can disrupt mobile communications, affecting enterprise mobile devices, IoT deployments, and critical infrastructure relying on cellular connectivity. Telecommunications providers could face network instability or customer service degradation if rogue base stations are deployed maliciously or accidentally. Industries such as finance, healthcare, transportation, and emergency services that depend on reliable mobile networks may experience operational interruptions. The lack of required user interaction or elevated privileges means attackers can exploit this vulnerability stealthily, increasing the risk of widespread service outages. Additionally, the presence of rogue base stations is a known tactic in advanced persistent threat (APT) campaigns, raising concerns about targeted attacks against high-value European entities. The impact on confidentiality and integrity is limited; however, availability degradation alone can have severe consequences in sectors requiring continuous connectivity.

To mitigate CVE-2025-20757, European organizations should prioritize the following actions: 1) Monitor vendor communications closely for the release of official patches (MOLY01673751) and apply them promptly to affected devices. 2) Implement network-level detection and prevention systems capable of identifying and blocking rogue base stations or suspicious cellular signals, leveraging IMSI catchers detection tools and anomaly-based monitoring. 3) Employ device management policies that restrict connections to untrusted or unknown base stations, where feasible. 4) Collaborate with mobile network operators to enhance network security and share threat intelligence regarding rogue base station activity. 5) For critical deployments, consider using multi-factor connectivity solutions that combine cellular with other communication channels to maintain availability during attacks. 6) Conduct regular security assessments and penetration testing focused on cellular network vulnerabilities. 7) Educate staff about the risks of rogue base stations and encourage reporting of unusual connectivity issues. These targeted measures go beyond generic patching and help reduce the attack surface and impact of this vulnerability.