@@ -190,6 +190,100 @@ User-visible Changes

   software that enumerates interfaces, looking for "broadcast capable?" and

   expecting certain results.  Normal uses should not see any difference.

+- The default configurations will no longer allow connections to OpenVPN 2.3.x

+  peer or earlier, use the new ``--compat-mode`` option if you need

+  compatibility with older versions. See the manual page on the

+  ``--compat-mode`` for details.

+

+Common errors with OpenSSL 3.0 and OpenVPN 2.6

+----------------------------------------------

+Both OpenVPN 2.6 and OpenSSL 3.0 tighten the security considerable, so some

+configuration will no longer work. This section will cover the most common

+causes and error message we have seen and explain their reason and temporary

+workarounds. You should fix the underlying problems as soon as possible since

+these workaround are not secure and will eventually stop working in a future

+update.

+

+- weak SHA1 or MD5 signature on certificates

+

+  This will happen on either loading of certificates or on connection

+  to a server::

+

+      OpenSSL: error:0A00018E:SSL routines::ca md too weak

+      Cannot load certificate file cert.crt

+      Exiting due to fatal error

+

+  OpenSSL 3.0 no longer allows weak signatures on certificates. You can

+  downgrade your security to allow them by using ``--tls-cert-profile insecure``

+  but should replace/regenerate these certificates as soon as possible.

+

+

+- 1024 bit RSA certificates, 1024 bit DH parameters, other weak keys

+

+  This happens if you use private keys or other cryptographic material that

+  does not meet today's cryptographic standards anymore. Messages are similar

+  to::

+

+      OpenSSL: error:0A00018F:SSL routines::ee key too small

+      OpenSSL: error:1408518A:SSL routines:ssl3_ctx_ctrl:dh key too small

+

+  DH parameters (``--dh``) can be regenerated with ``openssl dhparam 2048``.

+  For other cryptographic keys, these keys and certificates need to be

+  regenerated. TLS Security level can be temporarily lowered with

+  ``--tls-cert-profile legacy`` or even ``--tls-cert-profile insecure``.

+

+- Connecting to a OpenVPN 2.3.x server or allowing OpenVPN 2.3.x or earlier

+  clients

+

+  This will normally result in messages like::

+

+     OPTIONS ERROR: failed to negotiate cipher with server.  Add the server's cipher ('AES-128-CBC') to --data-ciphers (currently 'AES-256-GCM:AES-128-GCM:CHACHA20-POLY1305') if you want to connect to this server.

+

+     or

+

+     client/127.0.0.1:49954 SENT CONTROL [client]: 'AUTH_FAILED,Data channel cipher negotiation failed (no shared cipher)' (status=1)

+

+  You can manually add the missing cipher to the ``--data-ciphers``. The

+  standard ciphers should be included as well, e.g.

+  ``--data-ciphers AES-256-GCM:AES-128-GCM:?Chacha20-Poly1305:?AES-128-CBC``.

+  You can also use the ``--compat-mode`` option. Note that these message may

+  also indicate other cipher configuration problems. See the data channel

+  cipher negotiation manual section for more details. (Available online under

+  https://github.com/OpenVPN/openvpn/blob/master/doc/man-sections/cipher-negotiation.rst)

+

+- Use of a legacy or deprecated cipher (e.g. 64bit block ciphers)

+

+  OpenSSL 3.0 no longer supports a number of insecure and outdated ciphers in

+  its default configuration. Some of these ciphers are known to be vulnerable (SWEET32 attack).

+

+  This will typically manifest itself in messages like::

+

+      OpenSSL: error:0308010C:digital envelope routines::unsupported

+      Cipher algorithm 'BF-CBC' not found

+      Unsupported cipher in --data-ciphers: BF-CBC

+

+  If your OpenSSL distribution comes with the legacy provider (see

+  also ``man OSSL_PROVIDER-legacy``), you can load it with

+  ``--providers legacy default``.  This will re-enable the old algorithms.

+

+- OpenVPN version not supporting TLS 1.2 or later

+

+  The default in OpenVPN 2.6 and also in many distributions is now TLS 1.2 or

+  later. Connecting to a peer that does not support this will results in

+  messages like::

+

+    TLS error: Unsupported protocol. This typically indicates that client and

+    server have no common TLS version enabled. This can be caused by mismatched

+    tls-version-min and tls-version-max options on client and server. If your

+    OpenVPN client is between v2.3.6 and v2.3.2 try adding tls-version-min 1.0

+    to the client configuration to use TLS 1.0+ instead of TLS 1.0 only

+    OpenSSL: error:0A000102:SSL routines::unsupported protocol

+

+  This can be an OpenVPN 2.3.6 or earlier version. ``compat-version 2.3.0`` will

+  enable TLS 1.0 support if supported by the OpenSSL distribution. Note that

+  on some Linux distributions enabling TLS 1.1 or 1.0 is not possible.

+

+

 Overview of changes in 2.5

 ==========================