CVE-2021-31251

CRITICAL

Chiyu-tech BF-430/431/450M and SEMAC Firmware - Authentication Bypass via Malformed Telnet Request

Title source: llm
STIX 2.1

Exploitation Summary

EIP tracks 1 public exploit for CVE-2021-31251. PoCs published by sirpedrotavares.

AI-analyzed exploit summary This exploit bypasses telnet authentication on CHIYU IoT devices by sending malformed telnet negotiation packets, allowing an attacker to gain unauthorized shell access. The PoC establishes a connection and provides an interactive shell.

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.

Exploits (1)

exploitdb WORKING POC
by sirpedrotavares · pythonremotehardware
https://www.exploit-db.com/exploits/49936

This exploit bypasses telnet authentication on CHIYU IoT devices by sending malformed telnet negotiation packets, allowing an attacker to gain unauthorized shell access. The PoC establishes a connection and provides an interactive shell.

Classification
Working Poc 95%
Attack Type
Auth Bypass
Complexity
Trivial
Reliability
Reliable
Target: CHIYU BF-430, BF-431, BF-450M, and SEMAC devices (all firmware versions < June 2021)
No auth needed
Prerequisites: Network access to the target device's telnet port (23)
devstral-2 · analyzed Feb 16, 2026 Full analysis →

References (3)

Core 3

Scores

CVSS v3 9.8
EPSS 0.3571
EPSS Percentile 98.3%
Attack Vector NETWORK
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Details

CWE
CWE-287
Status published
Products (10)
chiyu-tech/bf-430_firmware
chiyu-tech/bf-431_firmware
chiyu-tech/bf-450m_firmware
chiyu-tech/semac_d1_firmware
chiyu-tech/semac_d2_firmware
chiyu-tech/semac_d2_n300_firmware
chiyu-tech/semac_d4_firmware
chiyu-tech/semac_s1_osdp_firmware
chiyu-tech/semac_s2_firmware
chiyu-tech/semac_s3v3_firmware
Published Jun 04, 2021
Tracked Since Feb 18, 2026