How severe is CVE-2021-31251?

CVE-2021-31251 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-31251 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 36% (98th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-31251?

CVE-2021-31251 primarily affects Chiyu-tech Bf-430 Firmware. In total, 10 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-31251?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2021-31251 published?

CVE-2021-31251 was published on 2021-06-04 and last updated on 2026-06-17.

CVE-2021-31251

CVE-2021-31251 is a critical-severity vulnerability in Chiyu-tech Bf-430 Firmware with a CVSS 3.x base score of 9.8. Its EPSS exploit-prediction score of 36% places it in the 98th percentile, indicating an elevated likelihood of exploitation. The underlying weakness is classified as CWE-287.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 7.5
EPSS exploit prediction: 36% (98th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-287
Affected product: Chiyu-tech Bf-430 Firmware
Published: 2021-06-04
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2021-31251?: 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.
How severe is CVE-2021-31251?: CVE-2021-31251 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-31251 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 36% (98th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-31251?: CVE-2021-31251 primarily affects Chiyu-tech Bf-430 Firmware. In total, 10 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-31251?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2021-31251 published?: CVE-2021-31251 was published on 2021-06-04 and last updated on 2026-06-17.

References

Affected products (10)

cpe:2.3:o:chiyu-tech:bf-430_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:chiyu-tech:bf-431_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:chiyu-tech:bf-450m_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:chiyu-tech:semac_s2_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:chiyu-tech:semac_d1_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:chiyu-tech:semac_d2_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:chiyu-tech:semac_d4_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:chiyu-tech:semac_s3v3_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:chiyu-tech:semac_d2_n300_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:chiyu-tech:semac_s1_osdp_firmware:-:*:*:*:*:*:*:*

More vulnerabilities in Chiyu-tech Bf-430 Firmware

CVE-2021-31249 — Medium (CVSS 6.5): A CRLF injection vulnerability was found on BF-430, BF-431, and BF-450M TCP/IP Converter devices from CHIYU Technology…
CVE-2021-31252 — Medium (CVSS 6.1): An open redirect vulnerability exists in BF-630, BF-450M, BF-430, BF-431, BF631-W, BF830-W, Webpass, and SEMAC devices…
CVE-2021-31641 — Medium (CVSS 6.1): An unauthenticated XSS vulnerability exists in several IoT devices from CHIYU Technology, including BF-630, BF-450M,…
CVE-2021-31250 — Medium (CVSS 5.4): Multiple storage XSS vulnerabilities were discovered on BF-430, BF-431 and BF-450M TCP/IP Converter devices from CHIYU…

All CVEs affecting Chiyu-tech Bf-430 Firmware →

Other CWE-287 (Improper Authentication) vulnerabilities

CVE-2026-45480 — Critical (CVSS 10.0): Improper authentication in Azure Active Directory allows an unauthorized attacker to elevate privileges over a network.
CVE-2026-46389 — Critical (CVSS 10.0): UDS Identity Config builds the Keycloak configuration image (realm, plugins, theme, truststore, JARs) consumed by UDS…
CVE-2026-10611 — Critical (CVSS 10.0): An authentication bypass vulnerability exists in MISP when LDAP mixed authentication is enabled with OTP enforcement.…
CVE-2026-47280 — Critical (CVSS 10.0): Improper authentication in Azure Resource Manager (ARM) allows an unauthorized attacker to elevate privileges over a…
CVE-2026-42822 — Critical (CVSS 10.0): Improper authentication in Azure Local Disconnected Operations allows an unauthorized attacker to elevate privileges…
CVE-2026-20182 — Critical (CVSS 10.0): May 2026: This security advisory provides the details and fix information for a vulnerability that was discovered and…

Browse all CWE-287 (Improper Authentication) vulnerabilities →