PSIRT Clarification: Cisco IOS and IOS XE Software Secure Shell Denial of Service Vulnerability

[Ivan91]

Summary

 

• A vulnerability in the Secure Shell (SSH) server code of Cisco IOS Software and Cisco IOS XE Software could allow an authenticated, remote attacker to cause an affected device to reload.

  The vulnerability is due to an internal state not being represented correctly in the SSH state machine, which leads to an unexpected behavior. An attacker could exploit this vulnerability by creating an SSH connection to an affected device and using a specific traffic pattern that causes an error condition within that connection. A successful exploit could allow an attacker to cause the device to reload, resulting in a denial of service (DoS) condition.

  Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability.

  I'm confused by the wording here, how could the remote hacker become authenticated, and if they're already authenticated, then isn't the damage already done?

  Thanks!

[Marius Gunnerud]

Well, is the damage already done? yes and no.  This depends on the privilege level that the attacker has gained.  If the attacker has only read privileges then the attacker could still exploit this vulnerability and cause a reload of the device.

If the attacker has write privileges then there is no need for the attacker to use this exploit as she or he can already do much more damage.