HOMEVULNERABILITIESCVE-2021-40524
HIGH

CVE-2021-40524

CWE-434Published: September 5, 2021· Updated: Jun 17, 2026

7.5
CVSS v3.1

Official 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.)

NVD Source

Technical Analysis

CVE-2021-40524 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in availability disruption (denial of service), with a CVSS base score of 7.5.

CVSS v3.1 Vector Breakdown

Exploitability
Attack VectorNetwork
Attack ComplexityLow
Privileges Req.None
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

Affected Vendors & Products

pureftpd1 product(s)
pure-ftpd
Source: NVD CPE · 1 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
External links open in a new tab. Always verify in a controlled environment before use.

Official Patches & Advisories

PATCHhttps://github.com/jedisct1/pure-ftpd/commit/37ad222868e52271905b94afea4fc780d83294b4
PATCHhttps://github.com/jedisct1/pure-ftpd/compare/1.0.49...1.0.50
PATCHhttps://github.com/jedisct1/pure-ftpd/commit/37ad222868e52271905b94afea4fc780d83294b4
PATCHhttps://github.com/jedisct1/pure-ftpd/compare/1.0.49...1.0.50
ADVISORYhttps://github.com/jedisct1/pure-ftpd/pull/158
ADVISORYhttps://github.com/jedisct1/pure-ftpd/pull/158

All References (7)

→
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

Quick Facts

CVE IDCVE-2021-40524
CVSS Score7.5 / 10
SeverityHIGH
WeaknessCWE-434
CISA KEVNo
Affected1 vendor(s)
PublishedSep 5, 2021

Related CVEs (CWE-434)

CVE-2024-34990
10.0
CVE-2024-32700
10.0
CVE-2024-34555
10.0
CVE-2021-38397
10.0
CVE-2024-31377
10.0
CVE-2020-24186
10.0

Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2021-40524 in threat intel feeds
  • →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWATCH.COM. CVE data is provided under the NVD usage policy.
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