CVE-2021-40524

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 4.3% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2021-09-05 · updated 2026-06-17
Weakness: CWE-434

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.)

Affected products

Pureftpd Pure-Ftpd: from 1.0.23 before 1.0.50 — fixed in 1.0.50

How to fix

Upgrade to a fixed version: Pureftpd Pure-Ftpd 1.0.50. Check the vendor advisory for mitigations.

References

https://github.com/jedisct1/pure-ftpd/commit/37ad222868e52271905b94afea4fc780d83294b4
https://github.com/jedisct1/pure-ftpd/compare/1.0.49...1.0.50
https://github.com/jedisct1/pure-ftpd/pull/158
https://github.com/jedisct1/pure-ftpd/commit/37ad222868e52271905b94afea4fc780d83294b4
https://github.com/jedisct1/pure-ftpd/compare/1.0.49...1.0.50
https://github.com/jedisct1/pure-ftpd/pull/158
https://lists.debian.org/debian-lts-announce/2025/11/msg00003.html

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