CVE-2026-20421

Modem crash via unvalidated out-of-bounds read

Published Feb 2, 2026 · Updated Feb 2, 2026

An out-of-bounds read in MediaTek chipset modems allows physically proximate attackers operating a rogue base station to crash the modem. The modem reads beyond a buffer after it improperly validates base-station input; MediaTek has not disclosed the affected routine or message type. Exploitation requires a user device to connect to the attacker-controlled base station, needs no privileges or user interaction, and interrupts modem service.

CVSS severity6.5
Medium
EPSS probability0.22%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

An out-of-bounds read in MediaTek chipset modems allows physically proximate attackers operating a rogue base station to crash the modem. The modem reads beyond a buffer after it improperly validates base-station input; MediaTek has not disclosed the affected routine or message type. Exploitation requires a user device to connect to the attacker-controlled base station, needs no privileges or user interaction, and interrupts modem service.

The record

CVE
CVE-2026-20421
Published
Feb 2, 2026
Updated
Feb 2, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-125, T1499.004
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 2, 2026CVE publishedPublication date reported by the CVE source.
  2. Feb 2, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

6.5CISA-ADPCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-125Out-of-bounds Read
T1499.004Endpoint Denial of Service: Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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