CVE-2021-31810: Trusting FTP PASV responses vulnerability in Net::FTP

A trusting FTP PASV responses vulnerability was discovered in Net::FTP. This vulnerability has been assigned the CVE identifier CVE-2021-31810. We strongly recommend upgrading Ruby.

net-ftp is a default gem in Ruby 3.0.1 but it has a packaging issue, so please upgrade Ruby itself.


A malicious FTP server can use the PASV response to trick Net::FTP into connecting back to a given IP address and port. This potentially makes Net::FTP extract information about services that are otherwise private and not disclosed (e.g., the attacker can conduct port scans and service banner extractions).

Affected Versions

  • Ruby 2.6 series: 2.6.7 and earlier
  • Ruby 2.7 series: 2.7.3 and earlier
  • Ruby 3.0 series: 3.0.1 and earlier


Thanks to Alexandr Savca for reporting the issue.


  • Originally published at 2021-07-07 09:00:00 UTC