An issue was discovered in Ruby through 2.5.8, 2.6.x through 2.6.6, and 2.7.x through 2.7.1. WEBrick, a simple HTTP server bundled with Ruby, had not checked the transfer-encoding header value rigorously. An attacker may potentially exploit this issue to bypass a reverse proxy (which also has a poor header check), which may lead to an HTTP Request Smuggling attack.

A flaw was found in Ruby. RubyGems cgi gem could allow a remote attacker to conduct spoofing attacks caused by the mishandling of security prefixes in cookie names in the CGI::Cookie.parse function. By sending a specially-crafted request, an attacker could perform cookie prefix spoofing attacks.

A flaw was found in the way the Ruby REXML library parsed XML documents. Parsing a specially crafted XML document using REXML and writing parsed data back to a new XML document results in creating a document with a different structure. This issue could affect the integrity of processed data in applications using REXML that parse XML documents, write data back to XML, and re-parse them again.

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).

References:

https://www.ruby-lang.org/en/news/2021/07/07/trusting-pasv-responses-in-net-ftp/

A buffer overrun vulnerability was discovered in CGI.escapehtml. This can lead to a buffer overflow when a user passes a very large string (> 700 MB) to CGI.escapehtml on a platform where long type takes 4 bytes, typically, Windows.