Synopsis
Similar to CVE-2018-10933, sending a USER_AUTH_SUCCESS message out of order allows a security feature bypass of certain authentication mechanisms in Cisco Small Business Switches. This could allow an attacker to bypass certificate-based authentication and use password-based authentication -- even if password authentication is disabled.
We tested on a variety of dated Cisco switches and firewalls, each of which had an OpenSSH version of SSH-2.0-OpenSSH_5.9p1.RL or prior. We could not replicate this on any version of mainline OpenSSH or later versions used in Cisco products. This isn't to say that this issue does not exist in other versions, but we were unable to confirm. Cisco was not able to provide us with a list of products -- supported or unsupported.
Solution
See vendor advisory for applicable patch or workaround.Proof of Concept
Disclosure Timeline
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