The CloudStack SAML authentication (disabled by default) does not enforce signature check. In CloudStack environments where SAML authentication is enabled, an attacker that initiates CloudStack SAML single sign-on authentication can bypass SAML authentication by submitting a spoofed SAML response with no signature and known or guessed username and other user details of a SAML-enabled CloudStack user-account. In such environments, this can result in a complete compromise of the resources owned and/or accessible by a SAML enabled user-account.

Affected users are recommended to disable the SAML authentication plugin by setting the "saml2.enabled" global setting to "false", or upgrade to version 4.18.2.2, 4.19.1.0 or later, which addresses this issue.