https://community.openvpn.net/openvpn/wiki/SecurityAnnouncem...

There was a serverside remote code execution vulnerability in OpenVPN less than a year ago.

OpenVPN is large and gnarly. It's not one of the better understood codebases. The assumption that software security assessors have closely inspected it would not be well-founded. It has had "formal" audits, but audits are point-in-time snapshots done under timebox conditions.

The point of WireGuard, from an assurance perspective, is that it's designed to mitigate these concerns. It is a VPN with most of the mechanism of legacy VPNs stripped out. Less mechanism = less attack surface. It's two orders of magnitude smaller than other VPNs in terms of lines of code. Less code = easier to review = more reviews. It's not just small: it's thoughtfully small, as the post we're commenting spells out.

OpenVPN is built on TLS. TLS is a complicated protocol. It needs to support a variety of different users and the complexity of that task shows in the protocol; that complexity (and legacy support) is also a big part of the vulnerability history of TLS. Ordinarily, it would be worth assuming the risks of TLS's complexity rather than building a custom transport protocol, because secure transport protocols can be tricky to get right. But WireGuard has had formal academic analysis (in addition to a Tamarin model) and inherits cryptographic design from work Trevor Perrin did. WireGuard's protocol only has to serve WireGuard's use case, and is significantly less likely to have cryptographic vulnerabilities than TLS or the OpenVPN system as a whole.

The right way to think about it is that OpenVPN is like Sendmail, and WireGuard is something closer to qmail.