OpenSSH Security Vulnerability information and patch details.

There’s a new security vulnerability in town that goes by the name of CVE-2016-0777 (and CVE-2016-0778). Catchy, I know.

In a nutshell, this is a leak in the OpenSSH client that can allow malicious servers to get the private key of a roaming client.

Obviously that is not a good thing.

This vulnerability works by exploiting an undocumented feature of OpenSSH client called “roaming” — a feature which allows the client, which has had a broken connection to the server, to reconnect to the server and resume a suspended SSH session. This feature is enabled by default in the OpenSSH client and contains a memory leak which could be exploited by a malicious or compromised SSH server.

First the bad news: This exploit exists in OpenSSH version 6.2 and, as such, is present in SUSE Linux Enterprise 11 SP3 — but only for keys over 4k.

Then the good news: We already have a security update available (and here) for SUSE Linux Enterprise 11 SP3 that patches this vulnerability.

And the even better news: While this bug is not exploitable in SUSE Linux Enterprise 11 SP4, 12 or 12 SP1 — each of those versions already use OpenSSH 6.6 — we have released patches to address the bug.

In addition, the vulnerable roaming code can be permanently disabled by adding the undocumented option “UseRoaming no” to the system-wide configuration file (usually /etc/ssh/ssh_config), or per user configuration file (~/.ssh/config), or command-line (-o “UseRoaming no”).

SUSE also recommends recreating all client keys, at least the important ones.  We have no reports, at this time, of this vulnerability being exploited.  But it is possible, so always better safe than sorry.

Thanks to Qualys for the detailed report of this issue.