Security News > 2023 > November > New SSH Vulnerability

For the first time, researchers have demonstrated that a large portion of cryptographic keys used to protect data in computer-to-server SSH traffic are vulnerable to complete compromise when naturally occurring computational errors occur while the connection is being established.

The vulnerability occurs when there are errors during the signature generation that takes place when a client and server are establishing a connection.

It affects only keys using the RSA cryptographic algorithm, which the researchers found in roughly a third of the SSH signatures they examined.

Of the roughly 1 billion RSA signatures, about one in a million exposed the private key of the host.

Abstract: We demonstrate that a passive network attacker can opportunistically obtain private RSA host keys from an SSH server that experiences a naturally arising fault during signature computation.

In prior work, this was not believed to be possible for the SSH protocol because the signature included information like the shared Diffie-Hellman secret that would not be available to a passive network observer.

News URL

https://www.schneier.com/blog/archives/2023/11/new-ssh-vulnerability.html