CVE-2021-21739

Signal disruption via unauthenticated optical module replacement

Published Aug 5, 2021 · Updated Aug 3, 2024

Authentication bypass in ZTE Corporation ZXCTN 6120H V5.10.00B24 allows physically proximate attackers to disrupt signal transmission. The transport access layer accepts a replacement optical module without sufficiently verifying its authenticity, so an unauthenticated module passes system authentication and detection. Physical access to replace the installed module is required, and the vendor reports signal-transmission disruption rather than data disclosure or administrative control.

CVSS severity2.6
Low
EPSS probability0.25%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authentication bypass in ZTE Corporation ZXCTN 6120H V5.10.00B24 allows physically proximate attackers to disrupt signal transmission. The transport access layer accepts a replacement optical module without sufficiently verifying its authenticity, so an unauthenticated module passes system authentication and detection. Physical access to replace the installed module is required, and the vendor reports signal-transmission disruption rather than data disclosure or administrative control.

The record

CVE
CVE-2021-21739
Published
Aug 5, 2021
Updated
Aug 3, 2024
Vendor
ZTE Corporation
Product
ZXCTN 6120H
Classifications
CWE-345, T1200
Attack vector
physical
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 5, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=<V5.10.00B24>

What conditions does exploitation require?

Attack vectorphysical
Required privilegesunauthenticated

What is affected?

ZTE Corporation · ZXCTN 6120Hversion=<V5.10.00B24>

Published CVSS scores

2.6ZTE CorporationCVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L
4.6NIST NVDCVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
2.1NIST NVDAV:L/AC:L/Au:N/C:N/I:P/A:N

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)
Vectorphysical
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-345Insufficient Verification of Data Authenticity
T1200Hardware Additions

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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