{
    "id": "CVE-2021-31251",
    "published": "2021-06-04 21:15:07",
    "last_modified": "2026-06-17 03:51:30",
    "cvss_score": "9.8",
    "cvss_severity": "CRITICAL",
    "cvss_version": "3.1",
    "cvss_vector": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
    "cwe": "CWE-287",
    "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.",
    "epss_score": "0.35714",
    "epss_percentile": "0.98414",
    "kev": 0,
    "kev_due": null,
    "has_exploit": 1,
    "updated_at": "2026-09-27 18:17:29",
    "priority": {
        "rank": 2,
        "label": "Patch early",
        "why": "A public exploit exists."
    },
    "products": [
        {
            "vendor": "chiyu-tech",
            "product": "bf-430"
        },
        {
            "vendor": "chiyu-tech",
            "product": "bf-430_firmware"
        },
        {
            "vendor": "chiyu-tech",
            "product": "bf-431"
        },
        {
            "vendor": "chiyu-tech",
            "product": "bf-431_firmware"
        },
        {
            "vendor": "chiyu-tech",
            "product": "bf-450m"
        },
        {
            "vendor": "chiyu-tech",
            "product": "bf-450m_firmware"
        },
        {
            "vendor": "chiyu-tech",
            "product": "semac_d1"
        },
        {
            "vendor": "chiyu-tech",
            "product": "semac_d1_firmware"
        },
        {
            "vendor": "chiyu-tech",
            "product": "semac_d2"
        },
        {
            "vendor": "chiyu-tech",
            "product": "semac_d2_firmware"
        },
        {
            "vendor": "chiyu-tech",
            "product": "semac_d2_n300"
        },
        {
            "vendor": "chiyu-tech",
            "product": "semac_d2_n300_firmware"
        },
        {
            "vendor": "chiyu-tech",
            "product": "semac_d4"
        },
        {
            "vendor": "chiyu-tech",
            "product": "semac_d4_firmware"
        },
        {
            "vendor": "chiyu-tech",
            "product": "semac_s1_osdp"
        },
        {
            "vendor": "chiyu-tech",
            "product": "semac_s1_osdp_firmware"
        },
        {
            "vendor": "chiyu-tech",
            "product": "semac_s2"
        },
        {
            "vendor": "chiyu-tech",
            "product": "semac_s2_firmware"
        },
        {
            "vendor": "chiyu-tech",
            "product": "semac_s3v3"
        },
        {
            "vendor": "chiyu-tech",
            "product": "semac_s3v3_firmware"
        }
    ],
    "kev_detail": null,
    "exploits": [
        {
            "source": "exploit-db",
            "ref_id": "49936",
            "title": "CHIYU IoT Devices - 'Telnet' Authentication Bypass",
            "date": "2021-06-03",
            "url": "https://www.exploit-db.com/exploits/49936"
        }
    ],
    "refs_list": [
        "https://gitbook.seguranca-informatica.pt/cve-and-exploits/cves/chiyu-iot-devices#cve-2021-31251",
        "https://seguranca-informatica.pt/dancing-in-the-iot-chiyu-devices-vulnerable-to-remote-attacks/#.YLqK1KhKguU",
        "https://www.chiyu-tech.com/msg/message-Firmware-update-87.html",
        "https://gitbook.seguranca-informatica.pt/cve-and-exploits/cves/chiyu-iot-devices#cve-2021-31251",
        "https://seguranca-informatica.pt/dancing-in-the-iot-chiyu-devices-vulnerable-to-remote-attacks/#.YLqK1KhKguU",
        "https://www.chiyu-tech.com/msg/message-Firmware-update-87.html"
    ]
}