Acrobat Reader DC version 21.007.20099 (and earlier), 20.004.30017 (and earlier) and 17.011.30204 (and earlier) are affected by a Violation of Secure Design Principles that could lead to a Security feature bypass. Acrobat Reader DC displays a warning message when a user clicks on a PDF file, which could be used by an attacker to mislead the user. In affected versions, this warning message does not include custom protocols when used by the sender. User interaction is required to abuse this vulnerability as they would need to click 'allow' on the warning message of a malicious file.