CVE-2026-20457: Modem Denial of Service Vulnerability

CVE-2026-20457 Overview

CVE-2026-20457 affects the MediaTek Modem component and stems from improper input validation [CWE-476]. A remote attacker operating a rogue base station can trigger a system crash on a connected User Equipment (UE), resulting in denial of service. Exploitation requires no additional execution privileges and no user interaction. MediaTek tracks the fix under Patch ID MOLY01826924 and Issue ID MSV-7301.

Critical Impact
A rogue base station within radio range can crash the modem of a connected device, disrupting cellular connectivity until the device recovers.

Affected Products

MediaTek Modem firmware (see MediaTek Security Bulletin July 2026)
Devices integrating affected MediaTek baseband chipsets
Vendor-specific product mapping published by MediaTek

Discovery Timeline

2026-07-01 - CVE-2026-20457 published to the National Vulnerability Database (NVD)
2026-07-01 - MediaTek Security Bulletin July 2026 released with patch details
2026-07-01 - Last updated in NVD database

Technical Details for CVE-2026-20457

Vulnerability Analysis

The vulnerability resides in the MediaTek Modem's handling of radio-layer input from a serving base station. When the modem receives malformed or unexpected input, insufficient validation leads to a null pointer dereference [CWE-476], causing the modem to crash. The result is a remote denial of service condition affecting cellular communication on the target device.

The attack is limited to the adjacent network. An attacker must be within radio range and must induce the target UE to attach to a base station under attacker control. Once attached, the attacker delivers the malformed signaling that triggers the fault path in the modem stack.

Root Cause

The root cause is improper input validation in a modem code path that dereferences a pointer before confirming it references a valid object. Attacker-controlled input from the base station reaches this path without sufficient sanitization, producing a null pointer dereference and a subsequent modem crash.

Attack Vector

Exploitation requires an attacker-controlled rogue base station. The attacker uses stronger signal power or selective jamming to attract the UE, then sends crafted signaling messages that reach the vulnerable modem handler. No credentials, prior access, or user interaction are required. Impact is limited to availability; confidentiality and integrity are not affected.

The vulnerability affects the modem baseband and does not by itself yield code execution. See the MediaTek Security Bulletin July 2026 for component-level technical details.

Detection Methods for CVE-2026-20457

Indicators of Compromise

Unexpected modem resets or repeated cellular disconnects on affected devices in a defined geographic area
Devices attaching to unknown or unauthorized cell IDs, PLMNs, or base stations with anomalously high signal strength
Kernel or radio interface layer (RIL) logs referencing modem crash traces or MOLY subsystem faults

Detection Strategies

Monitor mobile device management (MDM) telemetry for spikes in modem crash events or radio subsystem restarts across a fleet
Correlate cellular attachment logs to detect UEs connecting to base stations outside the expected operator list
Deploy IMSI catcher and rogue base station detection tooling in sensitive facilities

Monitoring Recommendations

Ingest device radio logs and MDM crash reports into a centralized analytics platform for baseline and anomaly detection
Alert on clusters of simultaneous modem failures across devices in the same location, which suggests a localized rogue base station
Track vendor advisories from MediaTek and downstream OEMs for patch adoption metrics across managed devices

How to Mitigate CVE-2026-20457

Immediate Actions Required

Apply the MediaTek modem patch referenced by Patch ID MOLY01826924 once distributed by the device OEM
Inventory devices with affected MediaTek chipsets and prioritize firmware updates through MDM
Restrict use of unpatched devices in high-risk physical environments where rogue base station attacks are plausible

Patch Information

MediaTek released the fix under Patch ID MOLY01826924 (Issue ID MSV-7301) in the MediaTek Security Bulletin July 2026. OEMs must integrate the modem firmware update into their device-level security patch level (SPL) and distribute it to end users through standard OTA channels.

Workarounds

Disable 2G or legacy radio modes on managed devices where the operating system exposes that control, reducing exposure to downgrade-based rogue base station attacks
Use MDM policy to enforce airplane mode or restrict cellular use in facilities equipped with rogue base station detection
Configure alerting on repeated modem crashes so operations teams can isolate affected devices quickly

bash

# Example: query Android device security patch level via ADB to confirm patch adoption
adb shell getprop ro.build.version.security_patch
adb shell getprop gsm.version.baseband