Version 1 (modified by 9 years ago) (diff) | ,
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The OpenSSL versions bundled in official Windows installers prior to 2.3.6-I002/I602 of OpenVPN are vulnerable to FREAK. OpenVPN users on *NIX typically get an updated OpenSSL version through their package management system and do not need to update OpenVPN.
Fortunately the vulnerability's impact on OpenVPN is fairly small:
- OpenVPN's tls-auth feature prevents this attack
- Adding !EXP to the server side tls-cipher is enough to mitigate attacks. The suggested tls-cipher string is DEFAULT:!EXP:!LOW:!PSK:!SRP:!kRSA. This disallows export ciphers, weak ciphers (e.g. DES), and RSA key exchange (note: not RSA authentication), but allows any future, stronger cipher suites.
- Clients who wish to rule out this attack before next week can add !kRSA to their tls-cipher
- An attacker requires a man-in-the-middle position
- An attacker has to invest time (~7.5 hrs) and money (~$100) per OpenVPN instance (restart) to attack a connection, which makes this relevant for targeted attacks only.
- OpenVPN always provides PFS with its own key exchange mechanism, making it impossible to decrypt sessions prior to a successful factorization of the temporary export key, even if those connections already used an RSA_EXPORT cipher.