CVE-2021-21745Known exploitationPublic exploitNetwork attack vector

Unauthorized API access via substring Referer check

Published Oct 20, 2021 · Updated Aug 3, 2024

Authentication bypass in ZTE MF971R firmware allows remote attackers to access router APIs through a crafted link visited by a user. The referer_check function uses strstr to accept any Referer containing 127.0.0.1 instead of verifying the request origin. A user must open the attacker-supplied URL; the bypass permits unauthorized API communication, including reading the remaining-login-attempt count.

CVSS severity4.7
Medium
EPSS probability55.71%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authentication bypass in ZTE MF971R firmware allows remote attackers to access router APIs through a crafted link visited by a user. The referer_check function uses strstr to accept any Referer containing 127.0.0.1 instead of verifying the request origin. A user must open the attacker-supplied URL; the bypass permits unauthorized API communication, including reading the remaining-login-attempt count.

The record

CVE
CVE-2021-21745
Published
Oct 20, 2021
Updated
Aug 3, 2024
Vendor
ZTE Corporation
Product
MF971R
Classifications
CWE-293, CWE-352, T1204.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 20, 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=BD_ZTE_MF971RV1.0.0B05, BD_PLKPLMF971R1V1.0.0B06, BD_MF971R2V1.0.0B03, BD_ZTE_MF971RS2V1.0.0B03, BD_ZTE_MF971RSV1.0.0B05

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

ZTE Corporation · MF971Rversion=BD_ZTE_MF971RV1.0.0B05, BD_PLKPLMF971R1V1.0.0B06, BD_MF971R2V1.0.0B03, BD_ZTE_MF971RS2V1.0.0B03, BD_ZTE_MF971RSV1.0.0B05

Published CVSS scores

4.3NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
4.7ZTE CorporationCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N
4.3NIST National Vulnerability DatabaseAV:N/AC:M/Au:N/C:N/I:P/A:N
4.7Cisco TalosCVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/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.

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 exploitationReported
Public exploitPublished

Weakness, pattern, technique

CWE-293Using Referer Field for Authentication
CWE-352Cross-Site Request Forgery (CSRF)
T1204.001Malicious Link

Public exploit references

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

Reported exploitation

Technologies

Your stack

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Your stack

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