How severe is CVE-2021-40524?

CVE-2021-40524 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-40524 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 4% (90th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-40524?

CVE-2021-40524 affects Pureftpd Pure-ftpd. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-40524?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-40524 published?

CVE-2021-40524 was published on 2021-09-05 and last updated on 2026-06-17.

CVE-2021-40524

CVE-2021-40524 is a high-severity vulnerability in Pureftpd Pure-ftpd with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-434.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
EPSS exploit prediction: 4% (90th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-434
Affected product: Pureftpd Pure-ftpd
Published: 2021-09-05
Last modified: 2026-06-17

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.)

Frequently asked questions

What is CVE-2021-40524?: 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.)
How severe is CVE-2021-40524?: CVE-2021-40524 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-40524 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 4% (90th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-40524?: CVE-2021-40524 affects Pureftpd Pure-ftpd. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-40524?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-40524 published?: CVE-2021-40524 was published on 2021-09-05 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:pureftpd:pure-ftpd:*:*:*:*:*:*:*:*

More vulnerabilities in Pureftpd Pure-ftpd

CVE-2017-12170 — Critical (CVSS 9.8): Downstream version 1.0.46-1 of pure-ftpd as shipped in Fedora was vulnerable to packaging error due to which the…
CVE-2024-48208 — High (CVSS 8.6): pure-ftpd before 1.0.52 is vulnerable to Buffer Overflow. There is an out of bounds read in the domlsd() function of…
CVE-2020-35359 — High (CVSS 7.5): Pure-FTPd 1.0.48 allows remote attackers to prevent legitimate server use by making enough connections to exceed the…
CVE-2020-9274 — High (CVSS 7.5): An issue was discovered in Pure-FTPd 1.0.49. An uninitialized pointer vulnerability has been detected in the diraliases…
CVE-2020-9365 — High (CVSS 7.5): An issue was discovered in Pure-FTPd 1.0.49. An out-of-bounds (OOB) read has been detected in the pure_strcmp function…
CVE-2019-20176 — High (CVSS 7.5): In Pure-FTPd 1.0.49, a stack exhaustion issue was discovered in the listdir function in ls.c.

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