[Bug 2019094] Re: [SRU] Focal: TLS 1.3 doesn't work on strict firewall/middlebox

Fri Jun 2 07:47:22 UTC 2023

Hi Andreas, this is what we tried in the User's environment:

$ cat /etc/gnutls/config
[global]
override-mode = blocklist

[overrides]
disabled-version = tls1.3

This didn't work at all.

Now, we did manage to temporarily solve the issue for the user by
editing their apache server conf file for landscape-server like so:

/etc/apache2/sites-available/<landscape-server>.conf

changing

   SSLProtocol all -SSLv3 -SSLv2 -TLSv1
to
   SSLProtocol all -SSLv3 -SSLv2 -TLSv1 -TLSv1.3

and restarted apache:

$ sudo systemctl reload apache2.service

This unblocked the user and they are currently happily doing their
upgrades with landscape working on Focal now. There is no urgent rush
anymore. This is now just down to regression risk vs benefit of this
user being able to turn on tls 1.3 again for Landscape and if any other
users will hit this in the wild.

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Title:
  [SRU] Focal: TLS 1.3 doesn't work on strict firewall/middlebox

Status in gnutls28 package in Ubuntu:
  Invalid
Status in gnutls28 source package in Focal:
  In Progress

Bug description:
  [ Impact ]

   * On Focal, the TLS 1.3 handshake might fail on strict
     (or misbehaving) proprietary firewall/middlebox that
     requires a non-empty Session ID (as TLS 1.2) per RFC.

   * The RFC specifies the ClientHello should always have
     a non-empty session ID, but this _is_ empty in Focal.

   * RFC 8446, Appendix D.4. Middlebox Compatibility Mode [1]
     """
     ... a significant number of middleboxes misbehave
     when a TLS client/server pair negotiates TLS 1.3.
     ... handshake look more like a TLS 1.2 handshake:

     -  The client always provides a non-empty session ID
        in the ClientHello, ...
     """

   * Reverse build dependencies that link against the
     static libraries in libgnutls28-dev
     would need No-Change Rebuilds to pick up this fix.
     (see `reverse-depends -b -r focal libgnutls28-dev`)

     However, none were found (details in comment #8).

  [ Test Plan ]

   * Check whether TLS 1.3 handshake has `Session ID:`

     - Focal (no):
        $ gnutls-cli --priority NORMAL:-VERS-ALL:+VERS-TLS1.3 ubuntu.com </dev/null
        ...
        - Description: (TLS1.3-X.509)-...
        - Options:
        - Handshake was completed
        ...

     - Jammy (yes):
        $ gnutls-cli --priority NORMAL:-VERS-ALL:+VERS-TLS1.3 ubuntu.com </dev/null
        ...
        - Description: (TLS1.3-X.509)-...
        - Session ID: CB:7D:DF:...
        - Options:
        - Handshake was completed
        ...

   * Check tests run at build time (`Testsuite summary for GnuTLS`).

     Tests passed per the build log from PPA with test packages:

        ===================================
        Testsuite summary for GnuTLS 3.6.13
        ===================================

   * Check autopkgtests from gnutls28 against PPA/SRU [4,6].

     Tests passed against PPA with test packages:

        autopkgtest [12:40:02]: @@@@@@@@@@@@@@@@@@@@ summary
        run-upstream-testsuite PASS

   * Check autopkgtests from reverse test triggers against PPA/SRU
     (see comment #12).

        $ reverse-depends -b -r focal src:gnutls28
        Reverse-Testsuite-Triggers
        * ...

   * (Internal) Verify the original reporter's proprietary
     firewall/middlebox now works with TLS 1.3 from GnuTLS.

  There is a test package available in the following ppa:

  https://launchpad.net/~mruffell/+archive/ubuntu/sf359157-test

  If you install the test package, the session ID is set
  correctly.

  [ Regression Potential ]

   * TLS 1.3 handshake now includes non-empty Session ID
     in ClientHello, so there's a behavior change in the
     Client side-only, but it does affect how particular
     Servers handle the client, depending on Session ID.

   * Thus, theoretically, if issues were to occur, that
     likely would manifest as client connection errors
     with TLS 1.3 (failures would be realized early and
     fast), and a workaround available is using TLS 1.2.

   * Even though changes to TLS handshake understandably
     may be scary (considering the impact of regressions),
     the proposed change is specified by the RFC (and is
     there to help w/ wider compatibility) and is already
     implemented in later versions (3.7.1 in Hirsute [5]).

  [ Other Info ]

   * Bionic is not impacted (TLS 1.2 only)
   * Jammy and later already fixed (TLS 1.3 on GnuTLS 3.7+)

  The fixes required are:

  commit e0bb98e1f71f94691f600839ff748d3a9f469d3e
  Author: Norbert Pocs <npocs at redhat.com>
  Date:   Fri Oct 30 17:18:30 2020 +0100
  Subject: Fix non-empty session id (TLS13_APPENDIX_D4)
  Link: https://gitlab.com/gnutls/gnutls/-/commit/e0bb98e1f71f94691f600839ff748d3a9f469d3e

  commit 5416fdc259d8df9b797d249f3e5d58789b2e2cf9
  Author: Daiki Ueno <ueno at gnu.org>
  Date:   Wed Feb 3 15:50:08 2021 +0100
  Subject: gnutls_session_is_resumed: don't check session ID in TLS 1.3
  Link: https://gitlab.com/gnutls/gnutls/-/commit/5416fdc259d8df9b797d249f3e5d58789b2e2cf9

  commit 05ee0d49fe93d8812ef220c7b830c4b3553ac4fd
  Author: Daiki Ueno <ueno at gnu.org>
  Date:   Sun Jan 24 07:34:24 2021 +0100
  Subject: handshake: TLS 1.3: don't generate session ID in resumption mode
  Link: https://gitlab.com/gnutls/gnutls/-/commit/05ee0d49fe93d8812ef220c7b830c4b3553ac4fd

  commit 24c9a24640c137b47bb1e8cc5fee2315f57219ad
  Author: Daiki Ueno <ueno at gnu.org>
  Date: Thu, 22 Apr 2021 16:42:01 +0200
  Subject: handshake: don't regenerate legacy_session_id in second CH after HRR
  Link: https://gitlab.com/gnutls/gnutls/-/commit/24c9a24640c137b47bb1e8cc5fee2315f57219ad

  [ Links ]

  [1] https://www.rfc-editor.org/rfc/rfc8446#appendix-D.4
  [4] https://autopkgtest.ubuntu.com/packages/g/gnutls28
  [5] https://launchpad.net/ubuntu/+source/gnutls28/3.7.1-3ubuntu1
  [6] https://autopkgtest.ubuntu.com/results/autopkgtest-focal-mruffell-sf359157-test/focal/amd64/g/gnutls28/20230524_124015_b6884@/log.gz

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