Univention Corporate Server 4.2 erratum 510 (security)

This update addresses the following issues:
* Privilege separation weakness related to PAM support (CVE-2015-6563)
* Use-after-free bug related to PAM support (CVE-2015-6564)
* possible fallback from untrusted to trusted X11 forwarding (CVE-2016-1908)
* missing sanitisation of input for X11 forwarding (CVE-2016-3115)
* Denial of service via very long passwords (CVE-2016-6515)
* loading of untrusted PKCS#11 modules in ssh-agent (CVE-2016-10009)
* Leak of host private key material to privilege-separated child process via
  realloc() (CVE-2016-10011)
* Bounds check can be evaded in the shared memory manager used by
  pre-authentication compression support (CVE-2016-10012)
* Out of sequence NEWKEYS message can allow remote attacker to cause denial
  of service (CVE-2016-10708)
* Improper write operations in readonly mode allow for zero-length file
  creation (CVE-2017-15906)