Security Fixes

• ​CVE-2023-46850 OpenVPN versions between 2.6.0 and 2.6.6 incorrectly use a send buffer after it has been free()d in some circumstances, causing some free()d memory to be sent to the peer. All configurations using TLS (e.g. not using --secret) are affected by this issue. (found while tracking down CVE-2023-46849 / Github ​#400, ​#417) ​
• CVE-2023-46849 OpenVPN versions between 2.6.0 and 2.6.6 incorrectly restore --fragment configuration in some circumstances, leading to a division by zero when --fragment is used. On platforms where division by zero is fatal, this will cause an OpenVPN crash. (Github ​#400, ​#417).

User visible changes

• DCO: warn if DATA_V1 packets are sent by the other side - this a hard incompatibility between a 2.6.x client connecting to a 2.4.0-2.4.4 server, and the only fix is to use --disable-dco.

• Remove OpenSSL Engine method for loading a key. This had to be removed because the original author did not agree to relicensing the code with the new linking exception added. This was a somewhat obsolete feature anyway as it only worked with OpenSSL 1.x, which is end-of-support.

• add warning if p2p NCP client connects to a p2mp server - this is a combination that used to work without cipher negotiation (pre 2.6 on both ends), but would fail in non-obvious ways with 2.6 to 2.6.

• add warning to --show-groups that not all supported groups are listed (this is due the internal enumeration in OpenSSL being a bit weird, omitting X448 and X25519 curves).

• --dns: remove support for exclude-domains argument (this was a new 2.6 option, with no backend support implemented yet on any platform, and it turns out that no platform supported it at all - so remove option again)

• warn user if INFO control message too long, do not forward to management client (safeguard against protocol-violating server implementations)

New features

• DCO-WIN: get and log driver version (for easier debugging).

• print "peer temporary key details" in TLS handshake

• log OpenSSL errors on failure to set certificate, for example if the algorithms used are in acceptable to OpenSSL (misleading message would be printed in cryptoapi / pkcs11 scenarios)

• add CMake build system for MinGW and MSVC builds

• remove old MSVC build system

• improve cmocka unit test building for Windows

Windows Client: Community MSI installer for Windows client can be found at Community Downloads.

Linux Packages: Instructions for installing community-maintained Linux packages can be found in the Community Wiki.

Full Changelog: https://github.com/OpenVPN/openvpn/compare/v2.6.6...v2.6.7