CVE-2021-40239Network attack vector

Memory corruption via unbounded RETR response formatting

Published Oct 11, 2021 · Updated Aug 4, 2024

Buffer overflow in Miniftpd 1.0 allows remote attackers to corrupt process memory by requesting an overlong retrieval path. The do_retr function in ftpproto.c writes sess->arg and fixed response text into a 1,024-byte stack buffer with sprintf, so the combined output can exceed the destination. NVD treats the FTP endpoint as remotely reachable without privileges, while public evidence establishes memory corruption but does not demonstrate code execution or a service crash.

CVSS severity9.8
Critical
EPSS probability1.41%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Buffer overflow in Miniftpd 1.0 allows remote attackers to corrupt process memory by requesting an overlong retrieval path. The do_retr function in ftpproto.c writes sess->arg and fixed response text into a 1,024-byte stack buffer with sprintf, so the combined output can exceed the destination. NVD treats the FTP endpoint as remotely reachable without privileges, while public evidence establishes memory corruption but does not demonstrate code execution or a service crash.

The record

CVE
CVE-2021-40239
Published
Oct 11, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-120, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 11, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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

7.5NVDAV:N/AC:L/Au:N/C:P/I:P/A:P
9.8NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

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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