CVE-2021-31251

Name: CVE-2021-31251
Creator: NVD / NIST
Published: 2021-06-04T21:15:07.517+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 9.8/10EPSS 35.71%

Last modified Jun 17, 2026

CVE-2021-31251 is a critical-severity vulnerability rated 9.8/10 on the CVSS scale. An authentication bypass in telnet server in BF-430 and BF431 232/422 TCP/IP Converter, BF-450M and SEMAC from CHIYU Technology Inc allows obtaining a privileged connection with the target device by supplying a specially malformed request and an attacker may force the remote telnet server to believe that the user has already authenticated.. EPSS estimates a 35.71% chance of exploitation in the next 30 days.

Description

An authentication bypass in telnet server in BF-430 and BF431 232/422 TCP/IP Converter, BF-450M and SEMAC from CHIYU Technology Inc allows obtaining a privileged connection with the target device by supplying a specially malformed request and an attacker may force the remote telnet server to believe that the user has already authenticated.

Metrics

CVSS 3.1

9.8/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS Probability

35.71%

98.3th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-287

Affected Software

Vendor	Product	Versions
Chiyu-Tech	Bf-430 Firmware	All versions
Chiyu-Tech	Bf-431 Firmware	All versions
Chiyu-Tech	Bf-450m Firmware	All versions
Chiyu-Tech	Semac S2 Firmware	All versions
Chiyu-Tech	Semac D1 Firmware	All versions
Chiyu-Tech	Semac D2 Firmware	All versions
Chiyu-Tech	Semac D4 Firmware	All versions
Chiyu-Tech	Semac S3v3 Firmware	All versions
Chiyu-Tech	Semac D2 N300 Firmware	All versions
Chiyu-Tech	Semac S1 Osdp Firmware	All versions

References

https://gitbook.seguranca-informatica.pt/cve-and-exploits/cves/chiyu-iot-devices#cve-2021-31251Exploit, Third Party Advisory
https://seguranca-informatica.pt/dancing-in-the-iot-chiyu-devices-vulnerable-to-remote-attacks/#.YLqK1KhKguUExploit, Third Party Advisory
https://www.chiyu-tech.com/msg/message-Firmware-update-87.htmlVendor Advisory
https://gitbook.seguranca-informatica.pt/cve-and-exploits/cves/chiyu-iot-devices#cve-2021-31251Exploit, Third Party Advisory
https://seguranca-informatica.pt/dancing-in-the-iot-chiyu-devices-vulnerable-to-remote-attacks/#.YLqK1KhKguUExploit, Third Party Advisory
https://www.chiyu-tech.com/msg/message-Firmware-update-87.htmlVendor Advisory

Timeline

Published: Jun 4, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-31251?

How severe is CVE-2021-31251?

CVE-2021-31251 has a CVSS score of 9.8/10 (CRITICAL severity). The EPSS model estimates a 35.71% probability of exploitation in the next 30 days.

How do I fix CVE-2021-31251?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-31251?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST