What is CVE-2021-40239?

CVE-2021-40239 is a critical-severity vulnerability in Miniftpd Project, classified under Buffer Copy without Checking Size of Input (Classic Buffer Overflow). CVSS score: 9.8/10. Published 2021-10-11.

How severe is CVE-2021-40239?

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

Is CVE-2021-40239 known to be exploited?

3 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Buffer overflow in Miniftpd Project

CVE-2021-40239

A Buffer Overflow vulnerability exists in the latest version of Miniftpd in the do_retr function in ftpproto.c

Vulnerability class: Buffer Overflow

Published 2021-10-11 · 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: 0.014 (71.6th percentile), scored 2026-10-01.

Low probability of exploitation in the next 30 days, but still tracked. 72nd percentile — 71.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.014 · newest: 0.014 · change: 0.000

Affected products

Miniftpd Project — versions 1.0

Weakness classification (CWE)

CWE-120 — Buffer Copy without Checking Size of Input (Classic Buffer Overflow)

Public proof-of-concept exploits

References

github.com/Gabe-commiter/Miniftpd/issues/2 (Exploit, Third Party Advisory)

Frequently asked questions

What is CVE-2021-40239?: CVE-2021-40239 is a critical-severity vulnerability in Miniftpd Project, classified under Buffer Copy without Checking Size of Input (Classic Buffer Overflow). CVSS score: 9.8/10. Published 2021-10-11.
How severe is CVE-2021-40239?: Critical severity. CVSS v3 base score is 9.8 out of 10.
Is CVE-2021-40239 known to be exploited?: 3 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.