RubyGems.org is the Ruby community gem host. A bug in password & email change confirmation code allowed an attacker to change their RubyGems.org account's email to an unowned email address. Having access to an account whose email has been changed could enable an attacker to save API keys for that account, and when a legitimate user attempts to create an account with their email (and has to reset password to gain access) and is granted access to other gems, the attacker would then be able to publish and yank versions of those gems. Commit number 90c9e6aac2d91518b479c51d48275c57de492d4d contains a patch for this issue.

RubyGems versions between 2.0.0 and 2.6.13 are vulnerable to a possible remote code execution vulnerability. YAML deserialization of gem specifications can bypass class white lists. Specially crafted serialized objects can possibly be used to escalate to remote code execution.

RubyGems version 2.6.12 and earlier is vulnerable to a DNS hijacking vulnerability that allows a MITM attacker to force the RubyGems client to download and install gems from a server that the attacker controls.

RubyGems version 2.6.12 and earlier fails to validate specification names, allowing a maliciously crafted gem to potentially overwrite any file on the filesystem.

RubyGems version 2.6.12 and earlier is vulnerable to maliciously crafted gem specifications to cause a denial of service attack against RubyGems clients who have issued a `query` command.

RubyGems version 2.6.12 and earlier is vulnerable to maliciously crafted gem specifications that include terminal escape characters. Printing the gem specification would execute terminal escape sequences.