CVE-2021-31645Public exploitNetwork attack vector

FTP access denial via connection-slot exhaustion

Published Jul 7, 2022 · Updated Aug 3, 2024

Denial of service in glFTPd 2.11a allows remote attackers to block legitimate FTP users by exhausting the server's connection limit. The daemon permits repeated unauthenticated connection attempts to occupy the finite connection allowance until subsequent FTP sessions are refused. The attack requires network reachability to the FTP port; per-IP limits require multiple source addresses, and the consequence is loss of new FTP access rather than a process crash.

CVSS severity7.5
High
EPSS probability1.90%
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 glFTPd 2.11a allows remote attackers to block legitimate FTP users by exhausting the server's connection limit. The daemon permits repeated unauthenticated connection attempts to occupy the finite connection allowance until subsequent FTP sessions are refused. The attack requires network reachability to the FTP port; per-IP limits require multiple source addresses, and the consequence is loss of new FTP access rather than a process crash.

The record

CVE
CVE-2021-31645
Published
Jul 7, 2022
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-770, T1499.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 7, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

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

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-770Allocation of Resources Without Limits or Throttling
T1499.002Service Exhaustion

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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