SSH1 with encryption disabled could allow client authentication to be forwarded

ssh-authentication-forwarding (6603) The risk level is classified as MediumMedium Risk


SSH (Secure Shell) with encryption disabled could allow client authentication to be forwarded if the client allows unknown host keys. An attacker can obtain a client's public host key during a connection attempt and use it to open and authenticate an SSH session to another server with the same access rights as the victim.


Gain Privileges


Upgrade to the latest version of SSH (2.4.0 or later), available from the SSH Secure Shell Download Page. See References.


  • SSH Communications Security Web site: SSH1 vulnerabilities.
  • CVE-2001-1473: The SSH-1 protocol allows remote servers to conduct man-in-the-middle attacks and replay a client challenge response to a target server by creating a Session ID that matches the Session ID of the target, but which uses a public key pair that is weaker than the target's public key, which allows the attacker to compute the corresponding private key and use the target's Session ID with the compromised key pair to masquerade as the target.
  • US-CERT VU#684820: SSH-1 allows client authentication to be forwarded by a malicious server to another server

Platforms Affected:

  • SSH SSH 1.2.24
  • SSH SSH 1.2.25
  • SSH SSH 1.2.26
  • SSH SSH 1.2.27
  • SSH SSH 1.2.28
  • SSH SSH 1.2.29
  • SSH SSH 1.2.30
  • SSH SSH 1.2.31


Jan 18, 2001

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