[USN-4233-2] GnuTLS update

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==========================================================================
Ubuntu Security Notice USN-4233-2
January 23, 2020

gnutls28 update
==========================================================================

A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 18.04 LTS
- Ubuntu 16.04 LTS

Summary:

USN-4233-1 marked SHA1 as untrusted in GnuTLS with no workaround.

Software Description:
- gnutls28: GNU TLS library

Details:

USN-4233-1 disabled SHA1 being used for digital signature operations in
GnuTLS. In certain network environments, certificates using SHA1 may still
be in use. This update adds the %VERIFY_ALLOW_BROKEN and
%VERIFY_ALLOW_SIGN_WITH_SHA1 priority strings that can be used to
temporarily re-enable SHA1 until certificates can be replaced with a
stronger algorithm.

Original advisory details:

As a security improvement, this update marks SHA1 as being untrusted for
digital signature operations.

Update instructions:

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 18.04 LTS:
libgnutls30 3.5.18-1ubuntu1.3

Ubuntu 16.04 LTS:
libgnutls30 3.4.10-4ubuntu1.7

In general, a standard system update will make all the necessary changes.

References:
https://usn.ubuntu.com/4233-2
https://usn.ubuntu.com/4233-1
https://launchpad.net/bugs/1860656

Package Information:
https://launchpad.net/ubuntu/+source/gnutls28/3.5.18-1ubuntu1.3
https://launchpad.net/ubuntu/+source/gnutls28/3.4.10-4ubuntu1.7