Is CVE-2021-40524 in the CISA KEV catalog?

No. CVE-2021-40524 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2021-40524?

CVE-2021-40524 has a CVSS v3 base score of 7.5 (HIGH).

What is the EPSS score for CVE-2021-40524?

CVE-2021-40524 has an EPSS score of 4.29% (90th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2021-40524?

Upgrade pure-ftpd on debian 11 to 1.0.49-4.1+deb11u1 or later.

CVE & CISA-KEV Catalog

CVE-2021-40524

HIGHEPSS 90th pctl

7.5

CVSS v3

NVD

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.)

CWE-434Unrestricted File Upload

How to fix

Remediation Available

pure-ftpdDebian

Fixed in:1.0.49-4.1+deb11u1CVE-2021-40524

Fixed in:1.0.50-1CVE-2021-40524

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityNone

AvailabilityHigh

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

Exploit Intelligence

4.29%probability of exploitation in 30 days

90thpercentile

Elevated risk: more likely to be exploited than 90% of all known CVEs.

References

Patch2

Exploit1

github.com

Other references1

lists.debian.org

Related Vulnerabilities

Other CWE-434 (Unrestricted File Upload) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2017-12617	High	8.1	100%	KEV	Fix
CVE-2018-15961	Critical	9.8	100%	KEV	-
CVE-2021-31207	Medium	6.6	100%	KEV + Ransom	Fix
CVE-2017-12615	High	8.1	100%	KEV + Ransom	-
CVE-2025-31324	Critical	10.0	99%	KEV + Ransom	-
CVE-2024-50623	Critical	9.8	99%	KEV + Ransom	Fix

Embed a live status badge for CVE-2021-40524

Markdown

[![CVE-2021-40524](https://tridentstack.com/cve/badge/CVE-2021-40524.svg)](https://tridentstack.com/cve/CVE-2021-40524)

HTML

<a href="https://tridentstack.com/cve/CVE-2021-40524"><img src="https://tridentstack.com/cve/badge/CVE-2021-40524.svg" alt="CVE-2021-40524"></a>

Find and fix vulnerabilities across your fleet

TridentStack Control continuously scans your Windows, macOS, and Linux fleet for known vulnerabilities, prioritizes them by severity and active exploitation, and patches them automatically.

Start free

This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2025-11-04.