{"id":"CVE-2021-31251","aliases":["EUVD-2021-18163","GHSA-fr6h-7w99-6jxc"],"status":"published","title":"An authentication bypass in telnet server in BF-430 and BF431 232/422 TCP/IP Converter, BF-450M...","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.","severity":{"version":"3.1","score":9.8,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"critical","assessor":"primary","from":"nvd"},"epss":{"day":"2026-11-12","score":0.35714,"percentile":0.98486,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":true,"fix_available":false},"cwes":["CWE-287"],"published":"2021-06-04T20:25:52Z","modified":"2026-06-17T03:51:30Z","exploits":[{"source":"exploitdb","id":"EDB-49936","title":"CHIYU IoT Devices - 'Telnet' Authentication Bypass","type":"remote","platform":"hardware","date":"2021-06-03","url":"https://www.exploit-db.com/exploits/49936"}],"products":[{"vendor":"chiyu-tech","product":"bf-430_firmware"},{"vendor":"chiyu-tech","product":"bf-431_firmware"},{"vendor":"chiyu-tech","product":"bf-450m_firmware"},{"vendor":"chiyu-tech","product":"semac_d1_firmware"},{"vendor":"chiyu-tech","product":"semac_d2_firmware"},{"vendor":"chiyu-tech","product":"semac_d2_n300_firmware"},{"vendor":"chiyu-tech","product":"semac_d4_firmware"},{"vendor":"chiyu-tech","product":"semac_s1_osdp_firmware"},{"vendor":"chiyu-tech","product":"semac_s2_firmware"},{"vendor":"chiyu-tech","product":"semac_s3v3_firmware"}],"references":[{"url":"https://www.chiyu-tech.com/msg/message-Firmware-update-87.html","tags":["x_refsource_CONFIRM","x_transferred","Vendor Advisory"]},{"url":"https://gitbook.seguranca-informatica.pt/cve-and-exploits/cves/chiyu-iot-devices#cve-2021-31251","tags":["x_refsource_MISC","x_transferred","Exploit","Third Party Advisory"]},{"url":"https://seguranca-informatica.pt/dancing-in-the-iot-chiyu-devices-vulnerable-to-remote-attacks/#.YLqK1KhKguU","tags":["x_refsource_MISC","x_transferred","Exploit","Third Party Advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2021-31251"},{"url":"https://github.com/advisories/GHSA-fr6h-7w99-6jxc"}],"sources":{"cve":[{"id":"CVE-2021-31251","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.","status":"published","published":"2021-06-04T20:25:52Z","modified":"2024-08-03T22:55:53.355Z","updated_at":"2026-11-02T14:33:05.665371Z"}],"euvd":[{"id":"EUVD-2021-18163","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.","status":"published","published":"2021-06-04T20:25:52Z","modified":"2024-08-03T22:55:53Z","updated_at":"2026-11-03T03:24:39.559154Z"}],"ghsa":[{"id":"GHSA-fr6h-7w99-6jxc","title":"An authentication bypass in telnet server in BF-430 and BF431 232/422 TCP/IP Converter, BF-450M...","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.","status":"published","published":"2022-05-24T19:04:00Z","modified":"2023-01-29T05:06:25Z","cwes":["CWE-287"],"updated_at":"2026-11-02T14:46:01.439998Z"}],"nvd":[{"id":"CVE-2021-31251","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.","status":"published","published":"2021-06-04T21:15:07.517Z","modified":"2026-06-17T03:51:30.403Z","cvss":[{"version":"3.1","score":9.8,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"critical","assessor":"primary"},{"version":"2.0","score":7.5,"vector":"AV:N/AC:L/Au:N/C:P/I:P/A:P","level":"high","assessor":"primary"}],"cwes":["CWE-287"],"updated_at":"2026-11-02T14:06:54.439974Z"}]}}