Skip to main content
Public proof of conceptFix available

CVE-2021-40524

A public proof of concept exists; no exploitation attested.

  • Published2021-09-05
  • Fixed in1.0.50
  • WeaknessCWE-434

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

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.)

Timeline

dates in UTC
  1. 2021-09-0519:15CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-11-03 15:37 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-40524?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-40524?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD
Pureftpd pure-ftpd
BranchAffectedFixed in
1.0≥ 1.0.23, < 1.0.501.0.50

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • pure-ftpdUbuntu:26.04:LTSall versions · no fixed version listed
  • pure-ftpdUbuntu:25.10all versions · no fixed version listed
  • pure-ftpdUbuntu:24.04:LTSall versions · no fixed version listed
  • pure-ftpdUbuntu:22.04:LTSall versions · no fixed version listed
  • pure-ftpdUbuntu:20.04:LTSall versions · no fixed version listed
  • pure-ftpdUbuntu:18.04:LTSall versions · no fixed version listed
  • pure-ftpdUbuntu:16.04:LTSall versions · no fixed version listed
  • pure-ftpdopenSUSE:Tumbleweedall versions · fixed in 1.0.50-1.1

3 more package ranges on OSV.dev

Vendor advisories

  • CVE-2021-40524 Red Hat Product Security

    pure-ftpd: unbounded file size in file upload

Full record on NVD

Fix

  1. Update Pureftpd pure-ftpd to 1.0.50

Advisories and patches

Detection

read 2026-11-02 22:42 UTC
Nuclei template
available
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
none listed
PoC-in-GitHub
Metasploit modules
none listed
Metasploit Framework

Sources

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Published
2021-09-05
Last Modified
2025-11-04
NVD status
Modified
GitHub Advisory
GHSA-p53v-96v3-p5jg

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.)

Is CVE-2021-40524 actively exploited?

Active exploitation of CVE-2021-40524 has not been confirmed. Its EPSS score was 4.3% on 2026-11-03, the estimated probability of exploitation in the next 30 days.

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

CVE-2021-40524 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

Running pure-ftpd? Hear about its next vulnerability

Surveillance reads the versions in your stack — a domain, a lockfile or a list — checks each CVE against the ranges its sources publish, and alerts you when one you run is exploited or enters CISA KEV. A version it cannot read stays « version not verified ».

Get alerts for this productCISA KEV additions, October 2026Search CVEs

No credit card required · No monthly cap on website lookups · 250 API requests/month

Go further

Related vulnerabilities

Same product first, then the same vendor advisory and the same publication week.

Back to CVE Database

Sources for this record