CVE-2020-19596Public exploitNetwork attack vector

Unauthenticated code execution via oversized SFTP username

Published Apr 5, 2021 · Updated Aug 4, 2024

Classic buffer overflow in Core FTP Server 1.2 Build 583 allows remote attackers to execute code via a crafted SFTP username. During SSH public-key connection setup, the server accepts an oversized username without enforcing the destination buffer bound, overwriting EIP after 198 bytes. Exploitation is unauthenticated but requires SSH-key authentication to be enabled; the published code-execution path is Windows-build dependent, while oversized usernames can hang the service.

CVSS severity9.8
Critical
EPSS probability1.29%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Classic buffer overflow in Core FTP Server 1.2 Build 583 allows remote attackers to execute code via a crafted SFTP username. During SSH public-key connection setup, the server accepts an oversized username without enforcing the destination buffer bound, overwriting EIP after 198 bytes. Exploitation is unauthenticated but requires SSH-key authentication to be enabled; the published code-execution path is Windows-build dependent, while oversized usernames can hang the service.

The record

CVE
CVE-2020-19596
Published
Apr 5, 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. Apr 5, 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

7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:P
9.8NIST NVDCVSS: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 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-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
T1190Exploit Public-Facing Application

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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