OpenSSH < 7.2 X11Forwarding Fallback Bypass Vulnerability

Medium Nessus Network Monitor Plugin ID 9311


The remote SSH server may be affected by an X11Forwarding fallback bypass vulnerability.


OpenSSH contains a flaw in ssh(1) that is triggered when it falls back from untrusted X11 forwarding to trusted forwarding when the X server disables the SECURITY extension. This may potentially result in X11 connections not being trusted.

Note: PVS has solely relied on the banner of the SSH client to perform this check. Any backported patches or workarounds such as recompiling or edited configurations are not observable through the banner.


Upgrade to OpenSSH version 7.2 or later.

See Also

Plugin Details

Severity: Medium

ID: 9311

Family: SSH

Published: 2016/04/22

Modified: 2016/11/23

Dependencies: 1997

Nessus ID: 90022

Risk Information

Risk Factor: Medium


Base Score: 5

Temporal Score: 4.1

Vector: CVSS2#AV:N/AC:L/Au:N/C:N/I:P/A:N

Temporal Vector: CVSS2#E:F/RL:OF/RC:C


Base Score: 5.3

Temporal Score: 4.9


Temporal Vector: CVSS3#E:F/RL:O/RC:C

Vulnerability Information

CPE: cpe:/a:openbsd:openssh

Patch Publication Date: 2016/02/29

Vulnerability Publication Date: 2016/02/29