Debian DLA-387-1 : openssh security update
Medium Nessus Plugin ID 87933
SynopsisThe remote Debian host is missing a security update.
DescriptionThe Qualys Security team discovered two vulnerabilities in the roaming
code of the OpenSSH client (an implementation of the SSH protocol
SSH roaming enables a client, in case an SSH connection breaks
unexpectedly, to resume it at a later time, provided the server also
The OpenSSH server doesn't support roaming, but the OpenSSH client
supports it (even though it's not documented) and it's enabled by
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.
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
This security update completely disables the roaming code in the
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.
- -- Yves-Alexis Perez
NOTE: Tenable Network Security has extracted the preceding description
block directly from the DLA security advisory. Tenable has attempted
to automatically clean and format it as much as possible without
introducing additional issues.
SolutionUpgrade the affected packages.