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| 5abd23 | Samuli Seppänen | 2025-02-27 10:26:17 | 1 | The OpenSSL versions bundled in official OpenVPN *Windows installers* prior to 2.3.6-I002/I602 are vulnerable to [FREAK](https://www.smacktls.com/). All users of the official OpenVPN Windows installers are encouraged to upgrade their OpenVPN installations or to take other measures (see below) to mitigate the attack. OpenVPN users on *NIX typically get an updated OpenSSL version through their package management system and do not need to update OpenVPN. |
| c4f02d | Samuli Seppänen | 2025-01-29 08:37:37 | 2 | |
| 5abd23 | Samuli Seppänen | 2025-02-27 10:26:17 | 3 | Fortunately the vulnerability's impact on OpenVPN is fairly small: |
| c4f02d | Samuli Seppänen | 2025-01-29 08:37:37 | 4 | |
| 5abd23 | Samuli Seppänen | 2025-02-27 10:26:17 | 5 | * If enabled, OpenVPN's tls-auth feature prevents this attack |
| 6 | * 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. |
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| 7 | * Clients who wish to rule out this attack on clients prior to 2.3.6-I002/I603 can add *!kRSA* to their tls-cipher string |
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| 8 | * An attacker requires a man-in-the-middle position. |
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| 9 | * An attacker has to invest time and money per OpenVPN instance (restart) to attack a connection, which makes this relevant for targeted attacks only. |
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| 10 | * 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. |