It was discovered that there was a user enumeration vulnerability in OpenSSH. A remote attacker could test whether a certain user exists on a target server.
For Debian 7 Wheezy, these problems have been fixed in version 6.0p1-4+deb7u8.
We recommend that you upgrade your openssh packages.
Further information about Extended LTS security advisories can be found at: https://deb.freexian.com/extended-lts/