CVE-2026-20479: Modem Out of Bounds Read DoS Vulnerability

CVE-2026-20479 Overview

CVE-2026-20479 is an out-of-bounds read vulnerability in the MediaTek Modem component. The flaw stems from a missing bounds check during message processing. An attacker operating a rogue base station can trigger the condition against a connected user equipment (UE) device, causing a remote denial of service. Exploitation requires no user interaction and no additional execution privileges. MediaTek tracks the fix under Patch ID MOLY00741071 and Issue ID MSV-7620. The weakness is classified as [CWE-125] Out-of-Bounds Read.

Critical Impact
A rogue base station can crash modem functionality on affected UE devices, disrupting cellular connectivity without authentication or user interaction.

Affected Products

MediaTek Modem firmware (see MediaTek Security Bulletin August 2026)
Devices integrating affected MediaTek baseband chipsets
UE devices attaching to attacker-controlled base stations

Discovery Timeline

2026-08-03 - CVE-2026-20479 published to NVD
2026-08-03 - Last updated in NVD database

Technical Details for CVE-2026-20479

Vulnerability Analysis

The vulnerability resides in the MediaTek Modem's handling of signaling messages received over the cellular air interface. A missing bounds check allows the modem firmware to read memory outside the expected buffer during message parsing. The out-of-bounds read leads to abnormal modem state and a denial-of-service condition on the target device. Because cellular baseband processing occurs before authentication of the network to the UE, an attacker running a rogue base station can transmit crafted radio messages that reach the vulnerable parser. The impact is limited to availability; the flaw does not grant code execution or leak confidential data according to the advisory metrics.

Root Cause

The root cause is the absence of a length or index validation step before dereferencing attacker-influenced offsets within a modem message buffer. When an incoming field specifies a size or offset larger than the underlying allocation, the parser reads adjacent memory, producing invalid state that terminates modem operation. This is a classic [CWE-125] Out-of-Bounds Read pattern in low-level protocol code.

Attack Vector

The attack vector is network-adjacent over the cellular radio interface. An attacker deploys a rogue base station within radio range of the target. The victim UE camps on the rogue cell, and the attacker delivers a malformed message that triggers the out-of-bounds read. No user interaction, credentials, or prior access are required. The vulnerability produces a remote denial of service rather than code execution.

No public exploit code has been released. Refer to the MediaTek Security Bulletin August 2026 for vendor technical details.

Detection Methods for CVE-2026-20479

Indicators of Compromise

Repeated, unexplained modem crashes or resets on MediaTek-based devices in a specific physical area.
Sudden loss of cellular service followed by re-attachment to an unknown or unexpected cell ID or PLMN.
Device logs showing baseband exceptions correlated with attachment to a low-signal, previously unseen base station.

Detection Strategies

Monitor mobile device management (MDM) telemetry for baseband reset events across MediaTek device fleets.
Correlate cellular attach anomalies (unexpected PLMN or cell ID changes) with device DoS symptoms.
Perform RF surveys in sensitive locations to detect unauthorized base stations broadcasting in licensed cellular bands.

Monitoring Recommendations

Track vendor bulletins and firmware update status across managed mobile inventory.
Alert on modem crash dumps or kernel logs referencing baseband recovery events.
Log and review cell tower attachment history from enterprise MDM or endpoint mobile agents where available.

How to Mitigate CVE-2026-20479

Immediate Actions Required

Apply the MediaTek modem firmware update referenced by Patch ID MOLY00741071 as delivered by device OEMs.
Inventory devices using affected MediaTek chipsets and prioritize firmware rollout through MDM channels.
Restrict use of high-value devices in physical areas where rogue base station activity is suspected until patched.

Patch Information

MediaTek published the fix in the MediaTek Security Bulletin August 2026 under Patch ID MOLY00741071 and Issue ID MSV-7620. OEMs integrate the patch into device-specific firmware updates. End users receive the fix through vendor OTA channels once the OEM ships the updated build.

Workarounds

Disable 2G/legacy radio access where the device platform permits, reducing exposure to downgrade attacks that force UE onto rogue cells.
Enforce policies through MDM to disable cellular radios on high-risk devices operating in untrusted RF environments.
Prefer Wi-Fi calling or VPN-tunneled connectivity for sensitive workflows until patched firmware is deployed.

bash

# Example MDM query to identify unpatched MediaTek devices
# (adapt to your MDM's query language)
SELECT device_id, model, baseband_version, os_version
FROM managed_devices
WHERE chipset_vendor = 'MediaTek'
  AND baseband_patch_level < '2026-08-01';