PatchTheCVECVE-2021-31251: An authentication bypass in telnet server in BF-430 and BF431 232/422 TCP/IP Converter, BF-450M and SEMAC from
CVE-2021-31251 is a critical-severity flaw (CVSS 9.8) affecting bf-430 firmware, bf-431 firmware, bf-450m firmware. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
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.
Why this priority
- Critical severity
- EPSS top 2%: very likely to be exploited
- Public exploit reference
- Remotely exploitable, no login, no user action
A fixed release or distro patch exists.
Risk facts
| CVSS score | 9.8 (Critical) |
| Attack vector | Network (remote) |
| Attack complexity | Low |
| Privileges needed | None |
| User interaction | None |
| EPSS exploit chance | 35.7% (top 2%) |
| CISA exploited list | No |
| Weakness | CWE-287 |
| Published | 2021-06-04 |
| Last modified | 2026-06-17 |
Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score
Am I affected?
Timeline
- Published CVE record published
- Updated Record last modified
Exact fixes by distribution
Public exploits and detection
Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.
- Write-up: gitbook.seguranca-informatica.pt/cve-and-exploits/cves/chiyu-iot-devices#cve-2021-31251
- Exploit-DB: CHIYU IoT Devices - 'Telnet' Authentication Bypass
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.
Quick answers
How do I fix CVE-2021-31251?
bf-430 firmware: mitigate or apply the listed mitigation; bf-431 firmware: mitigate or apply the listed mitigation; bf-450m firmware: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.
Is CVE-2021-31251 being exploited?
CVE-2021-31251 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.
What does CVE-2021-31251 affect?
CVE-2021-31251 affects bf-430 firmware, bf-431 firmware, bf-450m firmware. Severity is critical (CVSS 9.8). 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 a
How urgent is CVE-2021-31251?
Priority 69/100. Critical severity; EPSS top 2%: very likely to be exploited; Public exploit reference; Remotely exploitable, no login, no user action
Related CVEs
- CVE-2021-31641 MEDIUM 6.1 MITIGATE MITIGATE An unauthenticated XSS vulnerability exists in several IoT devices from CHIYU Technology, including BF-630, BF
- CVE-2021-31252 MEDIUM 6.1 MITIGATE MITIGATE An open redirect vulnerability exists in BF-630, BF-450M, BF-430, BF-431, BF631-W, BF830-W, Webpass, and SEMAC
- CVE-2021-31250 MEDIUM 5.4 MITIGATE MITIGATE Multiple storage XSS vulnerabilities were discovered on BF-430, BF-431 and BF-450M TCP/IP Converter devices fr
- CVE-2021-31249 MEDIUM 6.5 MITIGATE MITIGATE A CRLF injection vulnerability was found on BF-430, BF-431, and BF-450M TCP/IP Converter devices from CHIYU Te
- CVE-2020-8839 MEDIUM 6.1 UPGRADE Stored XSS was discovered on CHIYU BF-430 232/485 TCP/IP Converter devices before 1.16.00, as demonstrated by