Security readout for executives and security teams
Plain-English summary
Pure-FTPd versions 1.0.23 through 1.0.49 can mishandle file-size quota enforcement, allowing uploads to grow without the intended limit. The likely business impact is availability: storage exhaustion, denial of service, or a hung FTP server.
Executive priority
Prioritize remediation for internet-facing or business-critical FTP servers that accept uploads. This is not presented as code execution, but availability loss can still disrupt file transfer workflows and consume storage.
Technical view
The CVE describes an incorrect max_filesize quota mechanism in Pure-FTPd before 1.0.50. A greater-than-zero check did not account for an initial -1 value, allowing unbounded file uploads and potential denial of service or server hang.
Likely exposure
Exposure is limited to systems running Pure-FTPd 1.0.23 through 1.0.49, especially servers that permit authenticated or otherwise allowed file uploads. The source bundle does not provide affected CPEs or deployment-specific conditions.
Exploitation context
The bundle does not show KEV status or cited evidence of active exploitation. The described abuse path is availability-focused: bypassing the configured file-size quota behavior to cause excessive upload growth, denial of service, or server hang.
Researcher notes
Primary evidence is the CVE description and upstream Pure-FTPd PR, compare, and commit references. CVSS, CWE, and CPE data are absent in the provided bundle, so severity and exposure should be refined using local inventory and vendor package status.
Mitigation direction
- Upgrade Pure-FTPd to 1.0.50 or a vendor-supported patched package.
- Review Debian or distribution advisories for backported fixes.
- Restrict upload capability to trusted users where operationally possible.
- Monitor storage usage and FTP service health until remediation is complete.
Validation and detection
- Inventory hosts for Pure-FTPd version 1.0.23 through 1.0.49.
- Confirm package provenance for distribution backports that may retain older version strings.
- Review FTP service configuration for enabled upload paths and quota controls.
- Check monitoring for prior storage exhaustion or FTP service hangs.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CVE-2021-40524 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Unknown
- CVSS
- Not scored
- Known Exploited
- No
- Published
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS and timeline data
No CVSS vectors or timeline events were available in the normalized CVE source material.
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/jedisct1/pure-ftpd/pull/158CVE reference · x_refsource_MISC
- https://github.com/jedisct1/pure-ftpd/compare/1.0.49...1.0.50CVE reference · x_refsource_CONFIRM
- https://github.com/jedisct1/pure-ftpd/commit/37ad222868e52271905b94afea4fc780d83294b4CVE reference · x_refsource_CONFIRM
- https://lists.debian.org/debian-lts-announce/2025/11/msg00003.htmlCVE reference
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.