Univention Corporate Server 4.2 erratum 334 (security)

This update addresses the following issues:
* Double free vulnerability in the gnutls_x509_ext_import_proxy function
  allows remote attackers to have unspecified impact via crafted policy
  language information in an X.509 certificate with a Proxy Certificate
  Information extension. (CVE-2017-5334)
* The stream reading functions in lib/opencdk/read-packet.c allow remote
  attackers to cause a denial of service (out-of-memory error and crash) via
  a crafted OpenPGP certificate. (CVE-2017-5335)
* Stack-based buffer overflow in the cdk_pk_get_keyid function in
  lib/opencdk/pubkey.c allows remote attackers to have unspecified impact via
  a crafted OpenPGP certificate. (CVE-2017-5336)
* Multiple heap-based buffer overflows in the read_attribute function allow
  remote attackers to have unspecified impact via a crafted OpenPGP
  certificate. (CVE-2017-5337)
* GnuTLS is vulnerable to a NULL pointer dereference while decoding a status
  response TLS extension with valid contents. This could lead to a crash of
  the GnuTLS server application. (CVE-2017-7507)
* GnuTLS has an out-of-bounds write caused by an integer overflow and
  heap-based buffer overflow related to the cdk_pkt_read function in
  opencdk/read-packet.c. This issue is a subset of the vendor's
  GNUTLS-SA-2017-3 report. (CVE-2017-7869)