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


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.


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 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


Jan 18, 2001

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