CVE-2021-31810Network attack vector

Private-service probing via trusted PASV address

Published Jul 13, 2021 · Updated Aug 3, 2024

SSRF in Net::FTP in Ruby 2.6.7 and earlier, 2.7.0 through 2.7.3, and 3.0.0 through 3.0.1 allows remote attackers to probe private services. The parse227 method accepts the host and port from an untrusted PASV reply and opens the data connection to that supplied endpoint instead of the FTP control peer. An application must connect to an attacker-controlled FTP server in passive mode; successful abuse exposes reachable-service status and banners from the application's network position.

CVSS severity5.8
Medium
EPSS probability3.05%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

SSRF in Net::FTP in Ruby 2.6.7 and earlier, 2.7.0 through 2.7.3, and 3.0.0 through 3.0.1 allows remote attackers to probe private services. The parse227 method accepts the host and port from an untrusted PASV reply and opens the data connection to that supplied endpoint instead of the FTP control peer. An application must connect to an attacker-controlled FTP server in passive mode; successful abuse exposes reachable-service status and banners from the application's network position.

The record

CVE
CVE-2021-31810
Published
Jul 13, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-668, T1046
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 13, 2021CVE 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

5.0NIST NVDAV:N/AC:L/Au:N/C:P/I:N/A:N
5.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N
5.4Amazon LinuxCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
7.5SUSECVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

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 exploitUnconfirmed

Weakness, pattern, technique

CWE-668Exposure of Resource to Wrong Sphere
T1046Network Service Scanning

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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