CVE-2026-20527: Modem Remote Denial of Service Vulnerability

CVE-2026-20527 Overview

CVE-2026-20527 is a denial-of-service vulnerability in the MediaTek Modem component. The flaw stems from a missing bounds check [CWE-129] that can trigger a system crash when the user equipment (UE) processes crafted traffic from a rogue base station. Exploitation requires no user interaction and no additional execution privileges. The vulnerability is tracked by MediaTek under Patch IDs MOLY01864925 and MOLY01210562, and Issue ID MSV-8303. MediaTek disclosed the issue in its October 2026 Product Security Bulletin.

Critical Impact
An attacker operating a rogue base station within radio range can remotely crash the baseband of a connected UE, disrupting cellular connectivity until the device recovers.

Affected Products

MediaTek Modem (baseband firmware)
Devices identified in the MediaTek Security Bulletin - October 2026
Downstream OEM handsets and modules shipping impacted MediaTek chipsets

Discovery Timeline

2026-10-05 - CVE-2026-20527 published to NVD
2026-10-06 - Last updated in NVD database

Technical Details for CVE-2026-20527

Vulnerability Analysis

The vulnerability resides in the Modem subsystem, which handles cellular protocol processing in MediaTek baseband firmware. A code path consumes an attacker-influenced value without validating it against the expected range before using it as an index or size. When the UE attaches to a rogue base station, the attacker can send protocol messages that drive execution through the vulnerable path. The missing bounds check leads to invalid memory access and a modem crash, producing a remote denial-of-service condition on the affected device.

The weakness is classified under [CWE-129] Improper Validation of Array Index. Because baseband firmware mediates all cellular connectivity, a crash removes the device from the mobile network until the modem restarts. Confidentiality and integrity are not impacted, but availability of cellular services is lost for the duration of the fault.

Root Cause

The root cause is a missing bounds check on a value derived from radio-layer input. The vulnerable function processes a field without validating that it falls within the allocated structure or buffer boundaries. MediaTek's remediation is tracked under Patch IDs MOLY01864925 and MOLY01210562.

Attack Vector

Exploitation requires radio proximity. The attacker must stand up a rogue base station the UE will attach to, which raises attack complexity. Once attached, the attacker transmits a malformed message that reaches the vulnerable Modem code path. No user interaction and no credentials are required. The outcome is limited to a baseband crash; code execution is not reported.

No verified proof-of-concept code is published. See the MediaTek Security Bulletin - October 2026 for vendor-provided technical details.

Detection Methods for CVE-2026-20527

Indicators of Compromise

Unexpected baseband or modem crashes and automatic modem restarts on MediaTek-based devices
Repeated cellular disconnects correlated with presence in a specific physical location
Device logs showing modem subsystem resets without a corresponding OS fault

Detection Strategies

Collect modem crash telemetry from managed mobile fleets and alert on anomalous crash rates per device model
Monitor for unauthorized or unknown cell towers using mobile threat defense (MTD) agents capable of detecting rogue base stations
Correlate modem reset events with geolocation to identify clusters that may indicate a hostile radio environment

Monitoring Recommendations

Ingest mobile device management (MDM) and MTD telemetry into the SIEM and track baseband fault signatures over time
Review carrier-side signaling anomaly reports for repeated attach failures or protocol errors from managed devices
Track MediaTek bulletin advisories monthly and inventory affected chipset models across the mobile estate

How to Mitigate CVE-2026-20527

Immediate Actions Required

Identify devices using MediaTek chipsets listed in the October 2026 bulletin and prioritize them for patching
Apply vendor firmware updates incorporating Patch IDs MOLY01864925 and MOLY01210562 as OEMs release them
For high-risk users, restrict device operation to known trusted cellular environments until patches are deployed

Patch Information

MediaTek has released fixes referenced by Patch IDs MOLY01864925 and MOLY01210562, tracked under Issue ID MSV-8303. Patch delivery to end users depends on OEM and carrier integration cycles. Consult the MediaTek Security Bulletin - October 2026 and the device manufacturer's security advisories for availability.

Workarounds

Where supported, configure devices to prefer 5G standalone or restrict to known operator networks to reduce exposure to rogue base stations
Enable mobile threat defense features that detect anomalous base station behavior
Educate high-value users to disable cellular radios in untrusted physical environments until firmware updates are installed