SSH1 using DNS to resolve localhost could allow host key authentication to be bypassed

ssh-dns-authentication-bypass (6604) The risk level is classified as MediumMedium Risk

Description:

SSH (Secure Shell), if using a poisoned DNS (Domain Name System) server to resolve localhost, the host key authentication can be bypassed. Most SSH clients ask users to confirm the first-time acceptance of a host key, but this vulnerability allows the attacker to disable host key checking. An attacker could redirect an SSH connection to another host without the victim's knowledge.


Consequences:

Gain Privileges

Remedy:

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

References:

  • SSH Secure Shell Download Page: Download.
  • CVE-2001-1474: SSH before 2.0 disables host key checking when connecting to the localhost, which allows remote attackers to silently redirect connections to the localhost by poisoning the client's DNS cache.
  • OSVDB ID: 18231: SSH localhost Connection Host Key Check Bypass
  • US-CERT VU#786900: SSH host key authentication can be bypassed when DNS is used to resolve localhost

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

Reported:

Jan 18, 2001

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