CVE-2021-21727Network attack vector

Unauthenticated service interruption via crafted IPv6 packets

Published Mar 29, 2021 · Updated Aug 3, 2024

Denial of service in ZTE ZXHN F623 V6.0.0P3T33 and earlier allows remote attackers to interrupt the device via crafted IPv6 packets. The firmware processes the packets in a way that amplifies traffic until the appliance stops providing service; ZTE has not disclosed the responsible component or exact operation. The attack requires network reachability but no authentication or user interaction, and the published impact is limited to availability.

CVSS severity8.6
High
EPSS probability1.39%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in ZTE ZXHN F623 V6.0.0P3T33 and earlier allows remote attackers to interrupt the device via crafted IPv6 packets. The firmware processes the packets in a way that amplifies traffic until the appliance stops providing service; ZTE has not disclosed the responsible component or exact operation. The attack requires network reachability but no authentication or user interaction, and the published impact is limited to availability.

The record

CVE
CVE-2021-21727
Published
Mar 29, 2021
Updated
Aug 3, 2024
Vendor
ZTE Corporation
Product
ZXHN F623
Classifications
T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 29, 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

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=<ZXHN Z500 V1.0.0.2B1.1000 & ZXHN F670L V1.1.10P1N2E>

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

ZTE Corporation · ZXHN F623version=<ZXHN Z500 V1.0.0.2B1.1000 & ZXHN F670L V1.1.10P1N2E>

Published CVSS scores

7.5NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
8.6ZTE CorporationCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
7.8NVDAV:N/AC:L/Au:N/C:N/I:N/A:C

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

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

Weakness, pattern, technique

T1499Endpoint Denial of Service

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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