What is CVE-2021-27171?

CVE-2021-27171 is a critical-severity vulnerability in Fiberhome Hg6245d, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2021-02-10.

How severe is CVE-2021-27171?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Buffer overflow in Fiberhome Hg6245d

CVE-2021-27171

An issue was discovered on FiberHome HG6245D devices through RP2613. It is possible to start a Linux telnetd as root on port 26/tcp by using the CLI interface commands of ddd and shell (or tshell).

Vulnerability class: Buffer Overflow

Published 2021-02-10 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.178 (97.1th percentile), scored 2026-09-30.

Moderate probability of exploitation in the next 30 days — watch for active exploitation reports. 97th percentile — 97.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.178 · newest: 0.178 · change: 0.000

Affected products

Weakness classification (CWE)

CWE-787 — Out-of-bounds Write

References

pierrekim.github.io/blog/2021-01-12-fiberhome-ont-0day-vulnerabilities.html (Exploit, Third Party Advisory)

Frequently asked questions

What is CVE-2021-27171?: CVE-2021-27171 is a critical-severity vulnerability in Fiberhome Hg6245d, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2021-02-10.
How severe is CVE-2021-27171?: Critical severity. CVSS v3 base score is 9.8 out of 10.