CVE-2026-20534

Executive Summary

CVE-2026-20534 is an out-of-bounds read vulnerability in the MediaTek MT2716 modem firmware, arising from an incorrect bounds check during modem message processing. The flaw is remotely triggerable when a user equipment (UE) device is connected to an attacker-controlled rogue base station, requiring no user interaction and no additional execution privileges. Successful exploitation results in a remote denial of service (DoS) affecting the modem subsystem, with the primary impact being availability degradation of the device's cellular connectivity.

Technical Analysis

The vulnerability resides in the MT2716 modem firmware and is classified as CWE-125 (Out-of-bounds Read). The root cause is an "incorrect bounds check" — a logic or validation defect in the modem's parsing of input received over the radio interface. When the modem processes incoming data, it fails to correctly constrain a read operation within the intended buffer boundaries, causing it to read past the end of the allocated region.

This is distinct from an out-of-bounds write: there is no memory corruption or code execution implied. The direct consequence is the reading of adjacent memory, which may lead to unpredictable modem behavior, crashes, or a denial-of-service condition within the modem firmware itself. The CVSS vector (AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H) confirms the key characteristics of the flaw:

• Attack Vector (Adjacent, AV:A): Exploitation requires the attacker to be present on the same logical network segment — here, the air interface between the UE and a base station. The attacker does not need internet-routable access; physical/logical proximity to the victim device via the rogue radio link is the vector.
• Attack Complexity (High, AC:H): Exploitation requires specific conditions — an attacker-controlled rogue base station and a connected UE — making reliable triggering non-trivial.
• Privileges Required (None, PR:N) / User Interaction (None, UI:N): No credentials or user action are needed on the victim side.
• Confidentiality Impact (None, C:N): No data disclosure is expected from a read past buffer that results only in DoS.
• Integrity Impact (None, C:I:N): No modification of data is implied.
• Availability Impact (High, A:H): The vulnerable modem may become unavailable, disrupting cellular service on the affected device.

The attack surface is the modem's over-the-air message handling path — the set of routines that decode and act upon signaling received from the serving base station. Because the bounds check is incorrect, crafted signaling content can induce an out-of-bounds read.

The NVD description provides no further low-level detail (no function names, no specific message types, no buffer identifiers). The exact input structure required to trigger the flaw is not disclosed publicly. The vendor patch reference MOLY01797547 / Issue MSV-9155 indicates MediaTek has an internal track record for the fix, but no tracked source confirms a shipped patch.

Exploitation Scenarios

Note: No public proof-of-concept, exploit code, or Nuclei template exists for CVE-2026-20534. The attack chain below is inferred at the vulnerability-class level (out-of-bounds read triggered via malformed over-the-air signaling) consistent with the NVD description. No specific function names, message formats, or internal parameters are fabricated.

1. Reconnaissance / target identification. The attacker sets up equipment capable of acting as a rogue base station. Because the flaw is exploited over the air interface (CVSS AV:A), the attacker must be able to broadcast radio signals that the victim UE will attach to. The attacker identifies UEs in range that will associate with the rogue base station — typically by spoofing or advertising a legitimate-looking network identity.

2. Triggering the out-of-bounds read. Once a UE has connected to the attacker-controlled rogue base station, the attacker transmits crafted signaling messages to the victim device. The modem's incorrect bounds check fails to validate a read operation correctly, causing the modem to read beyond an intended buffer boundary. The exact message content is not publicly documented; the trigger is at the vulnerability class level: a malformed input that violates the implicit size assumption behind the flawed bounds check.

3. Payload / execution method. There is no payload execution in the classic remote code execution sense. The attack payload is the malformed over-the-air message itself. The out-of-bounds read occurs during modem processing, potentially resulting in a crash or hang of the modem firmware.

4. Post-exploitation impact. The immediate effect is a remote denial of service of the modem — loss of cellular connectivity (voice, data, SMS) for the duration of the malfunction. No persistence, no code execution, and no data exfiltration are indicated by the vulnerability class or CVSS subscores. Recovery may require modem reset or device reboot.

Impact Assessment

Business impact: For enterprises relying on cellular-connected devices — fleet telematics, IoT deployments, ruggedized field devices, or mobile workforces using MT2716-based hardware — a successful DoS against the modem disrupts connectivity for that device. While isolated to a single device per attack instance, targeted campaigns using rogue base stations (e.g., in a localized physical area) could degrade communications for multiple devices.

Affected systems: Devices whose firmware incorporates the MediaTek MT2716 modem codebase. The provided data lists no explicit affected version range, so all deployments using this modem subsystem should be considered potentially exposed until vendor guidance confirms otherwise.

Blast radius: Limited to availability of the modem function on affected device(s). CVSS scores the impact as Availability:High with Confidentiality:None and Integrity:None, scope Unchanged. The 5.3 Medium severity reflects the adjacency and high-complexity requirements that limit mass exploitation.

EPSS: 0.00182 (7.1% percentile) — indicating very low predicted likelihood of exploitation in the wild at this time. No CISA KEV listing and no known exploit code reinforce a low-activity profile.

Detection Guidance

Sigma Rule

title: Potential Modem Out-of-Bounds Read Exploitation Attempts (CVE-2026-20534)
id: 8f3a2c1e-5b7d-4a9f-9c2e-6d1f4b8a3e70
status: experimental
description: Detects repeated modem subsystem crashes or resets indicative of an out-of-bounds read triggered via rogue base station signaling affecting MediaTek MT2716 modem firmware.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-20534
author: valtersit.com
date: 2026-01-01
logsource:
  category: system
  product: android
detection:
  selection_crash:
    message|contains:
      - 'modem crash'
      - 'modem reset'
      - 'Fatal signal'
  selection_domain:
    message|contains:
      - 'MOLY01797547'
      - 'MSV-9155'
      - 'Modem'
  condition: selection_crash and selection_domain
falsepositives:
  - Legitimate modem firmware updates
  - Carrier-side network configuration changes
level: medium
tags:
  - attack.t1498
  - cve.2026.20534

YARA Rule

rule CVE_2026_20534_MediaTek_MT2716_Modem_OOB
{
    meta:
        description = "Detection heuristic for MediaTek MT2716 modem firmware versions potentially affected by CVE-2026-20534 out-of-bounds read"
        author = "valtersit.com"
        date = "2026-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-20534"
        cve = "CVE-2026-20534"
    strings:
        $mtk1 = "MT2716" ascii wide
        $mtk2 = "MOLY01797547" ascii wide
        $mtk3 = "MSV-9155" ascii wide
    condition:
        any of ($mtk*)
}

Suricata IDS Rule

alert udp any any -> any any (msg:"CVE-2026-20534 Potential Rogue Base Station Modem DoS Attempt - MediaTek MT2716"; flow:stateless; threshold: type both, track by_src, count 50, seconds 10; classtype:attempted-dos; reference:cve,2026-20534; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-20534; sid:2026205340; rev:1;)

Note: Because this vulnerability is triggered over the cellular radio interface and no public packet-level signature exists, the Suricata rule above is a high-volume anomaly heuristic that must be tuned against the monitored environment. It cannot decode cellular signaling on its own; it flags traffic-rate anomalies consistent with a fuzzing-style DoS.

Elastic Detection

sequence by host.id with maxspan=5m
  [any where event.category == "process" and process.name : ("rild", "qcrild", "mtkrild") and process.exit_code != 0]
  [any where event.category == "process" and process.name : ("rild", "qcrild", "mtkrild") and process.exit_code != 0]

Note: This detects repeated abnormal termination of the modem/RIL daemon consistent with an out-of-bounds read crashing modem firmware. Process names must be validated against the target platform.

Splunk SPL Query

index=android_logs (sourcetype=logcat OR sourcetype=syslog)
| search ("modem" AND ("crash" OR "reset" OR "Fatal signal" OR "MOLY01797547" OR "MSV-9155"))
| stats count by host, message
| where count > 3
| table host, message, count

Wazuh OSSEC Rule

<group name="cve-2026-20534,modem_dos">
  <rule id="100534" level="8">
    <decoded_as>syslog</decoded_as>
    <match>modem crash|modem reset|MOLY01797547|MSV-9155</match>
    <description>CVE-2026-20534: Possible MediaTek MT2716 modem out-of-bounds read / crash detected</description>
    <mitre>
      <id>T1498</id>
    </mitre>
    <group>availability_impact,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source). The vendor patch reference MOLY01797547 (Issue MSV-9155) exists, but no tracked source confirms an available or shipped firmware patch. Treat all affected MT2716 deployments as unpatched.

1. Immediate mitigations

   • Monitor vendor (MediaTek) and device OEM channels for firmware releases referencing MOLY01797547 / MSV-9155.
   • Where possible, restrict device attachment to trusted base stations / configured network operators and disable automatic attachment to unknown/unauthorized networks.
   • Implement monitoring for anomalous modem resets or crashes as indicators of exploitation attempts (see Detection Guidance).
   • For high-value devices, consider physical/proximity controls that limit adversary placement of rogue base stations near the asset.

2. Patch / upgrade steps

   • Obtain the firmware update that incorporates the MediaTek fix; follow OEM-specific update procedures.
   • Verify the patch reference (MOLY01797547) is incorporated before re-deploying devices.
   • Track the OEM advisory for the exact version that resolves the flaw, since no affected/fixed version ranges were provided in the source data.

3. Long-term hardening

   • Adopt a vendor firmware monitoring process for cellular modem components, which are frequently outside an organization's normal patch cadence.
   • Require modem vendors/OEMs to provide security advisories and patch SLAs as part of procurement.
   • Segment and monitor cellular-connected devices whose connectivity path is security-critical.
   • Deploy radio-interface anomaly detection where feasible to flag rogue base station activity.

References

• NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-20534
• CWE-125 — Out-of-bounds Read: https://cwe.mitre.org/data/definitions/125.html
• MITRE ATT&CK T1498 — Network Denial of Service: https://attack.mitre.org/techniques/T1498/
• MediaTek Product Security Advisories (vendor patch reference MOLY01797547 / Issue MSV-9155)
• CISA Known Exploited Vulnerabilities Catalog — CVE-2026-20534 is not listed as of this report

No known threat actor campaigns specific to CVE-2026-20534 have been identified in the provided data; no exploit code, PoC, or Nuclei template is publicly available. EPSS score is 0.00182, indicating low near-term exploitation likelihood.