CVE-2021-40524

Name: CVE-2021-40524
Creator: NVD / NIST
Published: 2021-09-05T19:15:15.08+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 7.5/10EPSS 4.39%

Last modified Jun 17, 2026

CVE-2021-40524 is a high-severity vulnerability rated 7.5/10 on the CVSS scale. In Pure-FTPd before 1.0.50, an incorrect max_filesize quota mechanism in the server allows attackers to upload files of unbounded size, which may lead to denial of service or a server hang. This occurs because a certain greater-than-zero test does not anticipate an initial -1 value. EPSS estimates a 4.39% chance of exploitation in the next 30 days.

Description

In Pure-FTPd before 1.0.50, an incorrect max_filesize quota mechanism in the server allows attackers to upload files of unbounded size, which may lead to denial of service or a server hang. This occurs because a certain greater-than-zero test does not anticipate an initial -1 value. (Versions 1.0.23 through 1.0.49 are affected.)

Metrics

CVSS 3.1

7.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS Probability

4.39%

90.1th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-434

Affected Software

Vendor	Product	Versions
Pureftpd	Pure-Ftpd	>= 1.0.23, < 1.0.50

References

https://github.com/jedisct1/pure-ftpd/commit/37ad222868e52271905b94afea4fc780d83294b4Patch, Third Party Advisory
https://github.com/jedisct1/pure-ftpd/compare/1.0.49...1.0.50Patch, Third Party Advisory
https://github.com/jedisct1/pure-ftpd/pull/158Exploit, Third Party Advisory
https://github.com/jedisct1/pure-ftpd/commit/37ad222868e52271905b94afea4fc780d83294b4Patch, Third Party Advisory
https://github.com/jedisct1/pure-ftpd/compare/1.0.49...1.0.50Patch, Third Party Advisory
https://github.com/jedisct1/pure-ftpd/pull/158Exploit, Third Party Advisory
https://lists.debian.org/debian-lts-announce/2025/11/msg00003.html

Timeline

Published: Sep 5, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-40524?

How severe is CVE-2021-40524?

CVE-2021-40524 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 4.39% probability of exploitation in the next 30 days.

How do I fix CVE-2021-40524?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-40524?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST