SWEET32 attacks the data channel cipher regardless of openvpn version .. so all openvpn versions using those ciphers are effected.
You are way too nice 🙂
The SWEET32 attack vector generally makes any ciphers using small cipher
blocks (not cipher
key length) smaller than 128 bits vulnerable. This is regardless of OpenVPN version, OpenSSL version, PolarSSL/mbed TLS versions. It is generally a weakness in the cipher algorithms itself. So this does not even target Blowfish alone. It also means all RC2, DES and 3DES algorithms are vulnerable to the very same SWEET32 attack, regardless of the application making use of any of these ciphers. The --reneg-bytes approach in OpenVPN is
not a real long-term solution, but it is considered to make you somewhat safer during a migration phase.
Bottom line is: Wherever you use Blowfish, RC2, DES/3DES or any other algorithm with cipher blocks smaller than 128 bits, they are to be considered vulnerable and you should migrate away from it ASAP.
With OpenVPN v2.4 on the server side you can get a fairly smooth migration possibility where you can update clients one-by-one as the server now supports clients using different --cipher algorithms. For more information about that, look at the --ncp-ciphers entry in the openvpn 2.4 man page.
