Debian Security Advisory

DLA-387-1 openssh -- LTS security update

Date Reported:
14 Jan 2016
Affected Packages:
Security database references:
In the Debian bugtracking system: Bug 810984.
In Mitre's CVE dictionary: CVE-2016-0777, CVE-2016-0778.
More information:

The Qualys Security team discovered two vulnerabilities in the roaming code of the OpenSSH client (an implementation of the SSH protocol suite).

SSH roaming enables a client, in case an SSH connection breaks unexpectedly, to resume it at a later time, provided the server also supports it.

The OpenSSH server doesn't support roaming, but the OpenSSH client supports it (even though it's not documented) and it's enabled by default.

  • CVE-2016-0777

    An information leak (memory disclosure) can be exploited by a rogue SSH server to trick a client into leaking sensitive data from the client memory, including for example private keys.

  • CVE-2016-0778

    A buffer overflow (leading to file descriptor leak), can also be exploited by a rogue SSH server, but due to another bug in the code is possibly not exploitable, and only under certain conditions (not the default configuration), when using ProxyCommand, ForwardAgent or ForwardX11.

This security update completely disables the roaming code in the OpenSSH client.

It is also possible to disable roaming by adding the (undocumented) option UseRoaming no to the global /etc/ssh/ssh_config file, or to the user configuration in ~/.ssh/config, or by passing -oUseRoaming=no on the command line.

Users with passphrase-less privates keys, especially in non interactive setups (automated jobs using ssh, scp, rsync+ssh etc.) are advised to update their keys if they have connected to an SSH server they don't trust.

More details about identifying an attack and mitigations can be found in the Qualys Security Advisory.