Published: August 8, 2017
Last Update: October 16, 2019
Vulnerability scans of the ACOS management interface indicate potential security exposures in the SSH, remote access service. Accordingly, the following vulnerabilities are addressed in this document.
|OpenSSH Xauth Command Injection Vulnerability
|Multiple CRLF injection vulnerabilities in session.c 
|OpenSSH LoginGraceTime Denial of Service Vulnerability
|openssh: Prevent connection slot exhaustion attacks 
Workarounds and Mitigations
Common security best practices in the industry for network appliance management and control planes can enhance protection against remote malicious attacks. Limit the exploitable attack surface for critical, infrastructure, networking equipment through the use of access lists or firewall filters to and from only trusted, administrative networks or hosts.
The following table shares brief descriptions for the vulnerabilities addressed in this document.
OpenSSH (OpenBSD Secure Shell) is a set of computer programs providing encrypted communication sessions over a computer network using the SSH protocol.
The sshd server fails to validate user-supplied X11 authentication credentials when establishing an X11 forwarding session. An authenticated user may inject arbitrary xauth commands by sending an x11 channel request that includes a newline character in the x11 cookie.
Please note that Systems with X11Forwarding enabled are affected.
Multiple CRLF injection vulnerabilities in session.c in sshd in OpenSSH before 7.2p2 allow remote authenticated users to bypass intended shell-command restrictions via crafted X11 forwarding data, related to the (1) do_authenticated1 and (2) session_x11_req functions.
OpenSSH (OpenBSD Secure Shell) is a set of computer programs providing encrypted communication sessions over a computer network using the SSH protocol. Default OpenSSH installations have an overly long LoginGraceTime and a lack of early connection release for MaxStartups settings. Remote unauthenticated attackers could bypass the LoginGraceTime and MaxStartups thresholds by intermittently transmitting a large number of new TCP connections to the targeted server. This could lead to connection slot exhaustion.
The default configuration of OpenSSH through 6.1 enforces a fixed time limit between establishing a TCP connection and completing a login, which makes it easier for remote attackers to cause a denial of service (connection-slot exhaustion) by periodically making many new TCP connections.
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