“This isn’t really a bug in the BinaryFormatter itself, nor a bug in MSMQ,” said watchTowr, “but rather the unfortunate consequence of Citrix relying on the documented-to-be-insecure BinaryFormatter to maintain a security boundary….
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https://www.csoonline.com/article/3604865/citrix-admins-advised-to-install-hotfixes-to-block-vulnerabilities.html