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openvpn/Changes.rst
Arne Schwabe 6dc09d0d45 Implement generating data channel keys via EKM/RFC 5705 
OpenVPN currently uses its own (based on TLS 1.0) key derivation
mechanism to generate the 256 bytes key data in key2 struct that
are then used used to generate encryption/hmac/iv vectors. While
this mechanism is still secure, it is not state of the art.

Instead of modernising our own approach, this commit implements
key derivation using the Keying Material Exporters API introduced
by RFC 5705.

We also use an opportunistic approach of negotiating the use of
EKM (exported key material) through an IV_PROTO flag and prefer
EKM to our own PRF if both client and server support it. The
use of EKM is pushed to the client as part of NCP as
key-derivation tls-ekm.

We still exchange the random data (112 bytes from client to server
and 64 byte from server to client) for the OpenVPN PRF but
do not use it. Removing that exchange would break the handshake
and make a key-method 3 or similar necessary.

As a side effect, this makes a little bit easier to have a FIPS compatible
version of OpenVPN since we do not rely on calling MD5 anymore.

Side note: this commit breaks the (not yet merged) WolfSSL support as it
claims to support EKM in the OpenSSL compat API but always returns an error
if you try to use it.

Patch v2: rebase/change to V2 of EKM refactoring

Patch v3: add Changes.rst

Patch v4: Rebase on master.

Patch v5: Refuse internal label to be used with --keying-material-exporter,
          polishing/fixes suggested by Steffan integrated

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Steffan Karger <steffan.karger@foxcrypto.com>
Message-Id: <20201009115453.4279-1-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg21187.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
2020-10-09 18:07:27 +02:00

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Overview of changes in 2.6
==========================
New features
------------
Keying Material Exporters (RFC 5705) based key generation
As part of the cipher negotiation OpenVPN will automatically prefer
the RFC5705 based key material generation to the current custom
OpenVPN PRF. This feature requires OpenSSL or mbed TLS 2.18+.
Overview of changes in 2.5
==========================
New features
------------
Client-specific tls-crypt keys (``--tls-crypt-v2``)
``tls-crypt-v2`` adds the ability to supply each client with a unique
tls-crypt key. This allows large organisations and VPN providers to profit
from the same DoS and TLS stack protection that small deployments can
already achieve using ``tls-auth`` or ``tls-crypt``.
ChaCha20-Poly1305 cipher support
Added support for using the ChaCha20-Poly1305 cipher in the OpenVPN data
channel.
Improved Data channel cipher negotiation
The option ``ncp-ciphers`` has been renamed to ``data-ciphers``.
The old name is still accepted. The change in name signals that
``data-ciphers`` is the preferred way to configure data channel
ciphers and the data prefix is chosen to avoid the ambiguity that
exists with ``--cipher`` for the data cipher and ``tls-cipher``
for the TLS ciphers.
OpenVPN clients will now signal all supported ciphers from the
``data-ciphers`` option to the server via ``IV_CIPHERS``. OpenVPN
servers will select the first common cipher from the ``data-ciphers``
list instead of blindly pushing the first cipher of the list. This
allows to use a configuration like
``data-ciphers ChaCha20-Poly1305:AES-256-GCM`` on the server that
prefers ChaCha20-Poly1305 but uses it only if the client supports it.
See the data channel negotiation section in the manual for more details.
Removal of BF-CBC support in default configuration:
By default OpenVPN 2.5 will only accept AES-256-GCM and AES-128-GCM as
data ciphers. OpenVPN 2.4 allows AES-256-GCM,AES-128-GCM and BF-CBC when
no --cipher and --ncp-ciphers options are present. Accepting BF-CBC can be
enabled by adding
data-ciphers AES-256-GCM:AES-128-GCM:BF-CBC
and when you need to support very old peers also
data-ciphers-fallback BF-CBC
To offer backwards compatibility with older configs an *explicit*
cipher BF-CBC
in the configuration will be automatically translated into adding BF-CBC
to the data-ciphers option and setting data-ciphers-fallback to BF-CBC
(as in the example commands above). We strongly recommend to switching
away from BF-CBC to a more secure cipher.
Asynchronous (deferred) authentication support for auth-pam plugin.
See src/plugins/auth-pam/README.auth-pam for details.
Deferred client-connect
The ``--client-connect`` option and the connect plugin API allow
asynchronous/deferred return of the configuration file in the same way
as the auth-plugin.
Faster connection setup
A client will signal in the ``IV_PROTO`` variable that it is in pull
mode. This allows the server to push the configuration options to
the client without waiting for a ``PULL_REQUEST`` message. The feature
is automatically enabled if both client and server support it and
significantly reduces the connection setup time by avoiding one
extra packet round-trip and 1s of internal event delays.
Netlink support
On Linux, if configured without ``--enable-iproute2``, configuring IP
addresses and adding/removing routes is now done via the netlink(3)
kernel interface. This is much faster than calling ``ifconfig`` or
``route`` and also enables OpenVPN to run with less privileges.
If configured with --enable-iproute2, the ``ip`` command is used
(as in 2.4). Support for ``ifconfig`` and ``route`` is gone.
Wintun support
On Windows, OpenVPN can now use ``wintun`` devices. They are faster
than the traditional ``tap9`` tun/tap devices, but do not provide
``--dev tap`` mode - so the official installers contain both. To use
a wintun device, add ``--windows-driver wintun`` to your config
(and use of the interactive service is required as wintun needs
SYSTEM privileges to enable access).
IPv6-only operation
It is now possible to have only IPv6 addresses inside the VPN tunnel,
and IPv6-only address pools (2.4 always required IPv4 config/pools
and IPv6 was the "optional extra").
Improved Windows 10 detection
Correctly log OS on Windows 10 now.
Linux VRF support
Using the new ``--bind-dev`` option, the OpenVPN outside socket can
now be put into a Linux VRF. See the "Virtual Routing and Forwarding"
documentation in the man page.
TLS 1.3 support
TLS 1.3 support has been added to OpenVPN. Currently, this requires
OpenSSL 1.1.1+.
The options ``--tls-ciphersuites`` and ``--tls-groups`` have been
added to fine tune TLS protocol options. Most of the improvements
were also backported to OpenVPN 2.4 as part of the maintainance
releases.
Support setting DHCP search domain
A new option ``--dhcp-option DOMAIN-SEARCH my.example.com`` has been
defined, and Windows support for it is implemented (tun/tap only, no
wintun support yet). Other platforms need to support this via ``--up``
script (Linux) or GUI (OSX/Tunnelblick).
per-client changing of ``--data-ciphers`` or ``data-ciphers-fallback``
from client-connect script/dir (NOTE: this only changes preference of
ciphers for NCP, but can not override what the client announces as
"willing to accept")
Handle setting of tun/tap interface MTU on Windows
If IPv6 is in use, MTU must be >= 1280 (Windows enforces IETF requirements)
Add support for OpenSSL engines to access private key material (like TPM).
HMAC based auth-token support
The ``--auth-gen-token`` support has been improved and now generates HMAC
based user token. If the optional ``--auth-gen-token-secret`` option is
used clients will be able to seamlessly reconnect to a different server
using the same secret file or to the same server after a server restart.
Improved support for pending authentication
The protocol has been enhanced to be able to signal that
the authentication should use a secondary authentication
via web (like SAML) or a two factor authentication without
disconnecting the OpenVPN session with AUTH_FAILED. The
session will instead be stay in a authenticated state and
wait for the second factor authentication to complete.
This feature currently requires usage of the managent interface
on both client and server side. See the `management-notes.txt`
``client-pending-auth`` and ``cr-response`` commands for more
details.
VLAN support
OpenVPN servers in TAP mode can now use 802.1q tagged VLANs
on the TAP interface to separate clients into different groups
that can then be handled differently (different subnets / DHCP,
firewall zones, ...) further down the network. See the new
options ``--vlan-tagging``, ``--vlan-accept``, ``--vlan-pvid``.
802.1q tagging on the client side TAP interface is not handled
today (= tags are just forwarded transparently to the server).
Support building of .msi installers for Windows
Allow unicode search string in ``--cryptoapicert`` option (Windows)
Support IPv4 configs with /31 netmasks now
(By no longer trying to configure ``broadcast x.x.x.x'' in
ifconfig calls, /31 support "just works")
New option ``--block-ipv6`` to reject all IPv6 packets (ICMPv6)
this is useful if the VPN service has no IPv6, but the clients
might have (LAN), to avoid client connections to IPv6-enabled
servers leaking "around" the IPv4-only VPN.
``--ifconfig-ipv6`` and ``--ifconfig-ipv6-push`` will now accept
hostnames and do a DNS lookup to get the IPv6 address to use
Deprecated features
-------------------
For an up-to-date list of all deprecated options, see this wiki page:
https://community.openvpn.net/openvpn/wiki/DeprecatedOptions
- ``ncp-disable`` has been deprecated
With the improved and matured data channel cipher negotiation, the use
of ``ncp-disable`` should not be necessary anymore.
- ``inetd`` has been deprecated
This is a very limited and not-well-tested way to run OpenVPN, on TCP
and TAP mode only, which complicates the code quite a bit for little gain.
To be removed in OpenVPN 2.6 (unless users protest).
- ``no-iv`` has been removed
This option was made into a NOOP option with OpenVPN 2.4. This has now
been completely removed.
- ``--client-cert-not-required`` has been removed
This option will now cause server configurations to not start. Use
``--verify-client-cert none`` instead.
- ``--ifconfig-pool-linear`` has been removed
This option is removed. Use ``--topology p2p`` or ``--topology subnet``
instead.
- ``--compress xxx`` is considered risky and is warned against, see below.
- ``--key-method 1`` has been removed
User-visible Changes
--------------------
- If multiple connect handlers are used (client-connect, ccd, connect
plugin) and one of the handler succeeds but a subsequent fails, the
client-disconnect-script is now called immediately. Previously it
was called, when the VPN session was terminated.
- Support for building with OpenSSL 1.0.1 has been removed. The minimum
supported OpenSSL version is now 1.0.2.
- The GET_CONFIG management state is omitted if the server pushes
the client configuration almost immediately as result of the
faster connection setup feature.
- ``--compress`` is nowadays considered risky, because attacks exist
leveraging compression-inside-crypto to reveal plaintext (VORACLE). So
by default, ``--compress xxx`` will now accept incoming compressed
packets (for compatibility with peers that have not been upgraded yet),
but will not use compression outgoing packets. This can be controlled with
the new option ``--allow-compression yes|no|asym``.
- Stop changing ``--txlen`` aways from OS defaults unless explicitly specified
in config file. OS defaults nowadays are actually larger then what we used
to configure, so our defaults sometimes caused packet drops = bad performance.
- remove ``--writepid`` pid file on exit now
- plugin-auth-pam now logs via OpenVPN logging method, no longer to stderr
(this means you'll have log messages in syslog or openvpn log file now)
- use ISO 8601 time format for file based logging now (YYYY-MM-DD hh:mm:dd)
(syslog is not affected, nor is ``--machine-readable-output``)
- ``--clr-verify`` now loads all CRLs if more than one CRL is in the same
file (OpenSSL backend only, mbedTLS always did that)
- when ``--auth-user-pass file`` has no password, and the management interface
is active, query management interface (instead of trying console query,
which does not work on windows)
- skip expired certificates in Windows certificate store (``--cryptoapicert``)
- ``--socks-proxy`` + ``--proto udp*`` will now allways use IPv4, even if
IPv6 is requested and available. Our SOCKS code does not handle IPv6+UDP,
and before that change it would just fail in non-obvious ways.
- TCP listen() backlog queue is now set to 32 - this helps TCP servers that
receive lots of "invalid" connects by TCP port scanners
- do no longer print OCC warnings ("option mismatch") about ``key-method``,
``keydir``, ``tls-auth`` and ``cipher`` - these are either gone now, or
negotiated, and the warnings do not serve a useful purpose.
- ``dhcp-option DNS`` and ``dhcp-option DNS6`` are now treated identically
(= both accept an IPv4 or IPv6 address for the nameserver)
Maintainer-visible changes
--------------------------
- the man page is now in maintained in .rst format, so building the openvpn.8
manpage from a git checkout now requires python-docutils (if this is missing,
the manpage will not be built - which is not considered an error generally,
but for package builders or ``make distcheck`` it is). Release tarballs
contain the openvpn.8 file, so unless some .rst is changed, doc-utils are
not needed for building.
- OCC support can no longer be disabled
- AEAD support is now required in the crypto library
- ``--disable-server`` has been removed from configure (so it is no longer
possible to build a client-/p2p-only OpenVPN binary) - the saving in code
size no longer outweighs the extra maintenance effort.
- ``--enable-iproute2`` will disable netlink(3) support, so maybe remove
that from package building configs (see above)
- support building with MSVC 2019
- cmocka based unit tests are now only run if cmocka is installed externally
(2.4 used to ship a local git submodule which was painful to maintain)
- ``--disable-crypto`` configure option has been removed. OpenVPN is now always
built with crypto support, which makes the code much easier to maintain.
This does not affect ``--cipher none`` to do a tunnel without encryption.
- ``--disable-multi`` configure option has been removed
Overview of changes in 2.4
==========================
New features
------------
Seamless client IP/port floating
Added new packet format P_DATA_V2, which includes peer-id. If both the
server and client support it, the client sends all data packets in
the new format. When a data packet arrives, the server identifies peer
by peer-id. If peer's ip/port has changed, server assumes that
client has floated, verifies HMAC and updates ip/port in internal structs.
This allows the connection to be immediately restored, instead of requiring
a TLS handshake before the server accepts packets from the new client
ip/port.
Data channel cipher negotiation
Data channel ciphers (``--cipher``) are now by default negotiated. If a
client advertises support for Negotiable Crypto Parameters (NCP), the
server will choose a cipher (by default AES-256-GCM) for the data channel,
and tell the client to use that cipher. Data channel cipher negotiation
can be controlled using ``--ncp-ciphers`` and ``--ncp-disable``.
A more limited version also works in client-to-server and server-to-client
scenarios where one of the end points uses a v2.4 client or server and the
other side uses an older version. In such scenarios the v2.4 side will
change to the ``--cipher`` set by the remote side, if permitted by by
``--ncp-ciphers``. For example, a v2.4 client with ``--cipher BF-CBC``
and ``ncp-ciphers AES-256-GCM:AES-256-CBC`` can connect to both a v2.3
server with ``cipher BF-CBC`` as well as a server with
``cipher AES-256-CBC`` in its config. The other way around, a v2.3 client
with either ``cipher BF-CBC`` or ``cipher AES-256-CBC`` can connect to a
v2.4 server with e.g. ``cipher BF-CBC`` and
``ncp-ciphers AES-256-GCM:AES-256-CBC`` in its config. For this to work
it requires that OpenVPN was built without disabling OCC support.
AEAD (GCM) data channel cipher support
The data channel now supports AEAD ciphers (currently only GCM). The AEAD
packet format has a smaller crypto overhead than the CBC packet format,
(e.g. 20 bytes per packet for AES-128-GCM instead of 36 bytes per packet
for AES-128-CBC + HMAC-SHA1).
ECDH key exchange
The TLS control channel now supports for elliptic curve diffie-hellmann
key exchange (ECDH).
Improved Certificate Revocation List (CRL) processing
CRLs are now handled by the crypto library (OpenSSL or mbed TLS), instead
of inside OpenVPN itself. The crypto library implementations are more
strict than the OpenVPN implementation was. This might reject peer
certificates that would previously be accepted. If this occurs, OpenVPN
will log the crypto library's error description.
Dualstack round-robin DNS client connect
Instead of only using the first address of each ``--remote`` OpenVPN
will now try all addresses (IPv6 and IPv4) of a ``--remote`` entry.
Support for providing IPv6 DNS servers
A new DHCP sub-option ``DNS6`` is added alongside with the already existing
``DNS`` sub-option. This is used to provide DNS resolvers available over
IPv6. This may be pushed to clients where `` --up`` scripts and ``--plugin``
can act upon it through the ``foreign_option_<n>`` environment variables.
Support for the Windows client picking up this new sub-option is added,
however IPv6 DNS resolvers need to be configured via ``netsh`` which requires
administrator privileges unless the new interactive services on Windows is
being used. If the interactive service is used, this service will execute
``netsh`` in the background with the proper privileges.
New improved Windows Background service
The new OpenVPNService is based on openvpnserv2, a complete rewrite of the OpenVPN
service wrapper. It is intended for launching OpenVPN instances that should be
up at all times, instead of being manually launched by a user. OpenVPNService is
able to restart individual OpenVPN processes if they crash, and it also works
properly on recent Windows versions. OpenVPNServiceLegacy tends to work poorly,
if at all, on newer Windows versions (8+) and its use is not recommended.
New interactive Windows service
The installer starts OpenVPNServiceInteractive automatically and configures
it to start at system startup.
The interactive Windows service allows unprivileged users to start
OpenVPN connections in the global config directory (usually
C:\\Program Files\\OpenVPN\\config) using OpenVPN GUI without any
extra configuration.
Users who belong to the built-in Administrator group or to the
local "OpenVPN Administrator" group can also store configuration
files under %USERPROFILE%\\OpenVPN\\config for use with the
interactive service.
redirect-gateway ipv6
OpenVPN has now feature parity between IPv4 and IPv6 for redirect
gateway including the handling of overlapping IPv6 routes with
IPv6 remote VPN server address.
LZ4 Compression and pushable compression
Additionally to LZO compression OpenVPN now also supports LZ4 compression.
Compression options are now pushable from the server.
Filter pulled options client-side: pull-filter
New option to explicitly allow or reject options pushed by the server.
May be used multiple times and is applied in the order specified.
Per-client remove push options: push-remove
New option to remove options on a per-client basis from the "push" list
(more fine-grained than ``--push-reset``).
Http proxy password inside config file
Http proxy passwords can be specified with the inline file option
``<http-proxy-user-pass>`` .. ``</http-proxy-user-pass>``
Windows version detection
Windows version is detected, logged and possibly signalled to server
(IV_PLAT_VER=<nn> if ``--push-peer-info`` is set on client).
Authentication tokens
In situations where it is not suitable to save user passwords on the client,
OpenVPN has support for pushing a --auth-token since v2.3. This option is
pushed from the server to the client with a token value to be used instead
of the users password. For this to work, the authentication plug-in would
need to implement this support as well. In OpenVPN 2.4 --auth-gen-token
is introduced, which will allow the OpenVPN server to generate a random
token and push it to the client without any changes to the authentication
modules. When the clients need to re-authenticate the OpenVPN server will
do the authentication internally, instead of sending the re-authentication
request to the authentication module . This feature is especially
useful in configurations which use One Time Password (OTP) authentication
schemes, as this allows the tunnel keys to be renegotiated regularly without
any need to supply new OTP codes.
keying-material-exporter
Keying Material Exporter [RFC-5705] allow additional keying material to be
derived from existing TLS channel.
Android platform support
Support for running on Android using Android's VPNService API has been added.
See doc/android.txt for more details. This support is primarily used in
the OpenVPN for Android app (https://github.com/schwabe/ics-openvpn)
AIX platform support
AIX platform support has been added. The support only includes tap
devices since AIX does not provide tun interface.
Control channel encryption (``--tls-crypt``)
Use a pre-shared static key (like the ``--tls-auth`` key) to encrypt control
channel packets. Provides more privacy, some obfuscation and poor-man's
post-quantum security.
Asynchronous push reply
Plug-ins providing support for deferred authentication can benefit from a more
responsive authentication where the server sends PUSH_REPLY immediately once
the authentication result is ready, instead of waiting for the the client to
to send PUSH_REQUEST once more. This requires OpenVPN to be built with
``./configure --enable-async-push``. This is a compile-time only switch.
Deprecated features
-------------------
For an up-to-date list of all deprecated options, see this wiki page:
https://community.openvpn.net/openvpn/wiki/DeprecatedOptions
- ``--key-method 1`` is deprecated in OpenVPN 2.4 and will be removed in v2.5.
Migrate away from ``--key-method 1`` as soon as possible. The recommended
approach is to remove the ``--key-method`` option from the configuration
files, OpenVPN will then use ``--key-method 2`` by default. Note that this
requires changing the option in both the client and server side configs.
- ``--tls-remote`` is removed in OpenVPN 2.4, as indicated in the v2.3
man-pages. Similar functionality is provided via ``--verify-x509-name``,
which does the same job in a better way.
- ``--compat-names`` and ``--no-name-remapping`` were deprecated in OpenVPN 2.3
and will be removed in v2.5. All scripts and plug-ins depending on the old
non-standard X.509 subject formatting must be updated to the standardized
formatting. See the man page for more information.
- ``--no-iv`` is deprecated in OpenVPN 2.4 and will be removed in v2.5.
- ``--keysize`` is deprecated in OpenVPN 2.4 and will be removed in v2.6
together with the support of ciphers with cipher block size less than
128-bits.
- ``--comp-lzo`` is deprecated in OpenVPN 2.4. Use ``--compress`` instead.
- ``--ifconfig-pool-linear`` has been deprecated since OpenVPN 2.1 and will be
removed in v2.5. Use ``--topology p2p`` instead.
- ``--client-cert-not-required`` is deprecated in OpenVPN 2.4 and will be removed
in v2.5. Use ``--verify-client-cert none`` for a functional equivalent.
- ``--ns-cert-type`` is deprecated in OpenVPN 2.3.18 and v2.4. It will be removed
in v2.5. Use the far better ``--remote-cert-tls`` option which replaces this
feature.
User-visible Changes
--------------------
- When using ciphers with cipher blocks less than 128-bits,
OpenVPN will complain loudly if the configuration uses ciphers considered
weak, such as the SWEET32 attack vector. In such scenarios, OpenVPN will by
default renegotiate for each 64MB of transported data (``--reneg-bytes``).
This renegotiation can be disabled, but is HIGHLY DISCOURAGED.
- For certificate DNs with duplicate fields, e.g. "OU=one,OU=two", both fields
are now exported to the environment, where each second and later occurrence
of a field get _$N appended to it's field name, starting at N=1. For the
example above, that would result in e.g. X509_0_OU=one, X509_0_OU_1=two.
Note that this breaks setups that rely on the fact that OpenVPN would
previously (incorrectly) only export the last occurrence of a field.
- ``proto udp`` and ``proto tcp`` now use both IPv4 and IPv6. The new
options ``proto udp4`` and ``proto tcp4`` use IPv4 only.
- ``--sndbuf`` and ``--recvbuf`` default now to OS defaults instead of 64k
- OpenVPN exits with an error if an option has extra parameters;
previously they were silently ignored
- ``--tls-auth`` always requires OpenVPN static key files and will no
longer work with free form files
- ``--proto udp6/tcp6`` in server mode will now try to always listen to
both IPv4 and IPv6 on platforms that allow it. Use ``--bind ipv6only``
to explicitly listen only on IPv6.
- Removed ``--enable-password-save`` from configure. This option is now
always enabled.
- Stricter default TLS cipher list (override with ``--tls-cipher``), that now
also disables:
* Non-ephemeral key exchange using static (EC)DH keys
* DSS private keys
- mbed TLS builds: changed the tls_digest_N values exported to the script
environment to be equal to the ones exported by OpenSSL builds, namely
the certificate fingerprint (was the hash of the 'to be signed' data).
- mbed TLS builds: minimum RSA key size is now 2048 bits. Shorter keys will
not be accepted, both local and from the peer.
- ``--connect-timeout`` now specifies the timeout until the first TLS packet
is received (identical to ``--server-poll-timeout``) and this timeout now
includes the removed socks proxy timeout and http proxy timeout.
In ``--static`` mode ``connect-timeout`` specifies the timeout for TCP and
proxy connection establishment
- ``--connect-retry-max`` now specifies the maximum number of unsuccessful
attempts of each remote/connection entry before exiting.
- ``--http-proxy-timeout`` and the static non-changeable socks timeout (5s)
have been folded into a "unified" ``--connect-timeout`` which covers all
steps needed to connect to the server, up to the start of the TLS exchange.
The default value has been raised to 120s, to handle slow http/socks
proxies graciously. The old "fail TCP fast" behaviour can be achieved by
adding "``--connect-timeout 10``" to the client config.
- ``--http-proxy-retry`` and ``--sock-proxy-retry`` have been removed. Proxy connections
will now behave like regular connection entries and generate a USR1 on failure.
- ``--connect-retry`` gets an optional second argument that specifies the maximum
time in seconds to wait between reconnection attempts when an exponential
backoff is triggered due to repeated retries. Default = 300 seconds.
- Data channel cipher negotiation (see New features section) can override
ciphers configured in the config file. Use ``--ncp-disable`` if you do not want
this behavior.
- All tun devices on all platforms are always considered to be IPv6
capable. The ``--tun-ipv6`` option is ignored (behaves like it is always
on).
- On the client side recursively routed packets, which have the same destination
as the VPN server, are dropped. This can be disabled with
--allow-recursive-routing option.
- On Windows, when the ``--register-dns`` option is set, OpenVPN no longer
restarts the ``dnscache`` service - this had unwanted side effects, and
seems to be no longer necessary with currently supported Windows versions.
- If no flags are given, and the interactive Windows service is used, "def1"
is implicitly set (because "delete and later reinstall the existing
default route" does not work well here). If not using the service,
the old behaviour is kept.
- OpenVPN now reloads a CRL only if the modication time or file size has
changed, instead of for each new connection. This reduces the connection
setup time, in particular when using large CRLs.
- OpenVPN now ships with more up-to-date systemd unit files which take advantage
of the improved service management as well as some hardening steps. The
configuration files are picked up from the /etc/openvpn/server/ and
/etc/openvpn/client/ directories (depending on unit file). This also avoids
these new unit files and how they work to collide with older pre-existing
unit files.
- Using ``--no-iv`` (which is generally not a recommended setup) will
require explicitly disabling NCP with ``--disable-ncp``. This is
intentional because NCP will by default use AES-GCM, which requires
an IV - so we want users of that option to consciously reconsider.
Maintainer-visible changes
--------------------------
- OpenVPN no longer supports building with crypto support, but without TLS
support. As a consequence, OPENSSL_CRYPTO_{CFLAGS,LIBS} and
OPENSSL_SSL_{CFLAGS,LIBS} have been merged into OPENSSL_{CFLAGS,LIBS}. This
is particularly relevant for maintainers who build their own OpenSSL library,
e.g. when cross-compiling.
- Linux distributions using systemd is highly encouraged to ship these new unit
files instead of older ones, to provide a unified behaviour across systemd
based Linux distributions.
- With OpenVPN 2.4, the project has moved over to depend on and actively use
the official C99 standard (-std=c99). This may fail on some older compiler/libc
header combinations. In most of these situations it is recommended to
use -std=gnu99 in CFLAGS. This is known to be needed when doing
i386/i686 builds on RHEL5.
Version 2.4.5
=============
New features
------------
- The new option ``--tls-cert-profile`` can be used to restrict the set of
allowed crypto algorithms in TLS certificates in mbed TLS builds. The
default profile is 'legacy' for now, which allows SHA1+, RSA-1024+ and any
elliptic curve certificates. The default will be changed to the 'preferred'
profile in the future, which requires SHA2+, RSA-2048+ and any curve.
Version 2.4.3
=============
New features
------------
- Support building with OpenSSL 1.1 now (in addition to older versions)
- On Win10, set low interface metric for TAP adapter when block-outside-dns
is in use, to make Windows prefer the TAP adapter for DNS queries
(avoiding large delays)
Security
--------
- CVE-2017-7522: Fix ``--x509-track`` post-authentication remote DoS
A client could crash a v2.4+ mbedtls server, if that server uses the
``--x509-track`` option and the client has a correct, signed and unrevoked
certificate that contains an embedded NUL in the certificate subject.
Discovered and reported to the OpenVPN security team by Guido Vranken.
- CVE-2017-7521: Fix post-authentication remote-triggerable memory leaks
A client could cause a server to leak a few bytes each time it connects to the
server. That can eventually cause the server to run out of memory, and thereby
causing the server process to terminate. Discovered and reported to the
OpenVPN security team by Guido Vranken. (OpenSSL builds only.)
- CVE-2017-7521: Fix a potential post-authentication remote code execution
attack on servers that use the ``--x509-username-field`` option with an X.509
extension field (option argument prefixed with ``ext:``). A client that can
cause a server to run out-of-memory (see above) might be able to cause the
server to double free, which in turn might lead to remote code execution.
Discovered and reported to the OpenVPN security team by Guido Vranken.
(OpenSSL builds only.)
- CVE-2017-7520: Pre-authentication remote crash/information disclosure for
clients. If clients use a HTTP proxy with NTLM authentication (i.e.
``--http-proxy <server> <port> [<authfile>|'auto'|'auto-nct'] ntlm2``),
a man-in-the-middle attacker between the client and the proxy can cause
the client to crash or disclose at most 96 bytes of stack memory. The
disclosed stack memory is likely to contain the proxy password. If the
proxy password is not reused, this is unlikely to compromise the security
of the OpenVPN tunnel itself. Clients who do not use the ``--http-proxy``
option with ntlm2 authentication are not affected.
- CVE-2017-7508: Fix remotely-triggerable ASSERT() on malformed IPv6 packet.
This can be used to remotely shutdown an openvpn server or client, if
IPv6 and ``--mssfix`` are enabled and the IPv6 networks used inside the VPN
are known.
- Fix null-pointer dereference when talking to a malicious http proxy
that returns a malformed ``Proxy-Authenticate:`` headers for digest auth.
- Fix overflow check for long ``--tls-cipher`` option
- Windows: Pass correct buffer size to ``GetModuleFileNameW()``
(OSTIF/Quarkslabs audit, finding 5.6)
User-visible Changes
--------------------
- ``--verify-hash`` can now take an optional flag which changes the hashing
algorithm. It can be either SHA1 or SHA256. The default if not provided is
SHA1 to preserve backwards compatibility with existing configurations.
- Restrict the supported ``--x509-username-field`` extension fields to subjectAltName
and issuerAltName. Other extensions probably didn't work anyway, and would
cause OpenVPN to crash when a client connects.
Bugfixes
--------
- Fix fingerprint calculation in mbed TLS builds. This means that mbed TLS users
of OpenVPN 2.4.0, v2.4.1 and v2.4.2 that rely on the values of the
``tls_digest_*`` env vars, or that use ``--verify-hash`` will have to change
the fingerprint values they check against. The security impact of the
incorrect calculation is very minimal; the last few bytes (max 4, typically
4) are not verified by the fingerprint. We expect no real-world impact,
because users that used this feature before will notice that it has suddenly
stopped working, and users that didn't will notice that connection setup
fails if they specify correct fingerprints.
- Fix edge case with NCP when the server sends an empty PUSH_REPLY message
back, and the client would not initialize it's data channel crypto layer
properly (trac #903)
- Fix SIGSEGV on unaligned buffer access on OpenBSD/Sparc64
- Fix TCP_NODELAY on OpenBSD
- Remove erroneous limitation on max number of args for ``--plugin``
- Fix NCP behaviour on TLS reconnect (Server would not send a proper
"cipher ..." message back to the client, leading to client and server
using different ciphers) (trac #887)
Version 2.4.2
=============
Bugfixes
--------
- Fix memory leak introduced in OpenVPN 2.4.1: if ``--remote-cert-tls`` is
used, we leaked some memory on each TLS (re)negotiation.
Security
--------
- Fix a pre-authentication denial-of-service attack on both clients and
servers. By sending a too-large control packet, OpenVPN 2.4.0 or v2.4.1 can
be forced to hit an ASSERT() and stop the process. If ``--tls-auth`` or
``--tls-crypt`` is used, only attackers that have the ``--tls-auth`` or
``--tls-crypt`` key can mount an attack.
(OSTIF/Quarkslab audit finding 5.1, CVE-2017-7478)
- Fix an authenticated remote DoS vulnerability that could be triggered by
causing a packet id roll over. An attack is rather inefficient; a peer
would need to get us to send at least about 196 GB of data.
(OSTIF/Quarkslab audit finding 5.2, CVE-2017-7479)
Version 2.4.1
=============
- ``--remote-cert-ku`` now only requires the certificate to have at least the
bits set of one of the values in the supplied list, instead of requiring an
exact match to one of the values in the list.
- ``--remote-cert-tls`` now only requires that a keyUsage is present in the
certificate, and leaves the verification of the value up to the crypto
library, which has more information (i.e. the key exchange method in use)
to verify that the keyUsage is correct.
- ``--ns-cert-type`` is deprecated. Use ``--remote-cert-tls`` instead.
The nsCertType x509 extension is very old, and barely used.
``--remote-cert-tls`` uses the far more common keyUsage and extendedKeyUsage
extension instead. Make sure your certificates carry these to be able to
use ``--remote-cert-tls``.
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