[Bug 1866611] Re: OpenVPN w. SHA1 signed CA broken after upgrade to 1.1.1d-2ubuntu6

[Dimitri John Ledkov]

The status of this bug is invalid, because we will not downgrade default
security level to the one that allows broken crypto to be used by
default. And instructions on how to self-compromise systems are
available and are currently known to work.

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Title:
  OpenVPN w. SHA1 signed CA broken after upgrade to 1.1.1d-2ubuntu6

Status in openssl package in Ubuntu:
  Invalid

Bug description:
  After upgrading openssl on my Focal-install this morning (upgrade
  openssl:amd64 1.1.1d-2ubuntu3 1.1.1d-2ubuntu6 per /var/log/dpkg.log),
  my OpenVPN tunnel refuses to connect to our corporate VPN (from
  /var/log/syslog):

  corp-laptop nm-openvpn[4688]: VERIFY ERROR: depth=0, error=CA signature digest algorithm too weak: C=DK, ST=None, L=Copenhagen, O=XX, OU=XX, CN=XX, emailAddress=XX
  corp-laptop nm-openvpn[4688]: OpenSSL: error:1416F086:SSL routines:tls_process_server_certificate:certificate verify failed

  I'm told we're running a SHA1-signed CA, which we're guessing has been
  deprecated somewhere between -2ubuntu3 and -2ubuntu6. The changelog
  for -2ubuntu4 mentions importing some upstream changes, but isn't more
  specific than that:
  https://changelogs.ubuntu.com/changelogs/pool/main/o/openssl/openssl_1.1
  .1d-2ubuntu4/changelog

  As a work-around, the internet suggests two work-arounds (neither of
  which has worked for me):

  1) Adding the following to /etc/defaults/openssl:

      OPTARGS="--tls-cipher DEFAULT:@SECLEVEL=0"

  2) Adding the following to /etc/ssl/openssl.conf:

      CipherString    = :@SECLEVEL=1

  I also tried rolling back the package, but the old version doesn't
  seem to be available:

      $ sudo apt install openssl=1.1.1d-2ubuntu3
      ...
      E: Version '1.1.1d-2ubuntu3' for 'openssl' was not found

  
  I am no SSL-expert and would appreciate any pointers to get around this. (Our network-dept. does not have the bandwidth to roll over our CA on short notice, so I will need some other way to move ahead).

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