CVE-2021-31251: Chiyu-Tech Bf-430 Firmware

Critical severity, CVSS 9.8. EPSS: 35.7% chance of exploitation in the next 30 days.

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.

Affected products

• Chiyu-Tech Bf-430 Firmware: affected versions not specified
• Chiyu-Tech Bf-431 Firmware: affected versions not specified
• Chiyu-Tech Bf-450m Firmware: affected versions not specified
• Chiyu-Tech Semac d1 Firmware: affected versions not specified
• Chiyu-Tech Semac d2 Firmware: affected versions not specified
• Chiyu-Tech Semac d2 n300 Firmware: affected versions not specified
• Chiyu-Tech Semac d4 Firmware: affected versions not specified
• Chiyu-Tech Semac s1 Osdp Firmware: affected versions not specified
• Chiyu-Tech Semac s2 Firmware: affected versions not specified
• Chiyu-Tech Semac s3v3 Firmware: affected versions not specified

Published 2021-06-04. Last modified 2026-06-17.