CVE-2021-4432Public exploitNetwork attack vector

Unauthenticated service interruption via USER command

Published Jan 16, 2024 · Updated Jun 17, 2025

Denial of service in PCMan FTP Server 2.0.7 allows remote attackers to interrupt the FTP service through the USER command handler. The public record identifies the USER handler as the locus but does not disclose the malformed input or internal operation that triggers the failure. No authentication or user interaction is required; the documented consequence is limited to availability, and public sources do not specify whether the process hangs or crashes.

CVSS severity7.5
High
EPSS probability1.32%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in PCMan FTP Server 2.0.7 allows remote attackers to interrupt the FTP service through the USER command handler. The public record identifies the USER handler as the locus but does not disclose the malformed input or internal operation that triggers the failure. No authentication or user interaction is required; the documented consequence is limited to availability, and public sources do not specify whether the process hangs or crashes.

The record

CVE
CVE-2021-4432
Published
Jan 16, 2024
Updated
Jun 17, 2025
Vendor
PCMan
Product
PCMan FTP Server
Classifications
CWE-404, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 16, 2024CVE publishedPublication date reported by the CVE source.
  2. Jun 17, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=2.0.7

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

PCMan · PCMan FTP Serverversion=2.0.7

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.0VulDB CNAAV:N/AC:L/Au:N/C:N/I:N/A:P
5.3VulDB CNACVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-404Improper Resource Shutdown or Release
T1499Endpoint Denial of Service

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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