Introduction

On 19th March 2015 the OpenSSL project made a new release which fixed a number of security vulnerabilities. This page discussed the impact of those vulnerabilities to OpenVPN. The content on this page is mostly taken from an email thread on openvpn-user mailing list (thanks Steffan!).

Vulnerabilities that may affect OpenVPN

Depending on your configuration and OpenSSL version used, the following advisories from the list can apply to OpenVPN setups:

Reclassified: RSA silently downgrades to EXPORT_RSA [Client] (CVE-2015-0204)
Segmentation fault in ASN1_TYPE_cmp (CVE-2015-0286)
ASN.1 structure reuse memory corruption (CVE-2015-0287)
Base64 decode (CVE-2015-0292)
Use After Free following d2i_ECPrivatekey error (CVE-2015-0209)
- OpenVPN 2.3, the current version, does not support EC certs yet. Note however that the git master branch does.

The following vulnerabilities affect OpenSSL 1.0.2 only, which is quite new and not yet used very often. Moreover, the official OpenVPN Windows installers bundle OpenSSL 1.0.1, which is not vulnerable:

Multiblock corrupted pointer (CVE-2015-0290)
OpenSSL 1.0.2 !ClientHello sigalgs DoS (CVE-2015-0291)
Segmentation fault for invalid PSS parameters (CVE-2015-0208)
Empty CKE with client auth and DHE (CVE-2015-1787)

Vulnerabilities that do not affect OpenVPN

The following do not apply to OpenVPN:

Segmentation fault in DTLSv1_listen (CVE-2015-0207)
OpenVPN does not use DTLS
PKCS7 NULL pointer dereferences (CVE-2015-0289)
TLS does not use PKCS!#7
DoS via reachable assert in SSLv2 servers (CVE-2015-0293)
OpenVPN only does TLSv1.0+
Handshake with unseeded PRNG (CVE-2015-0285)
OpenVPN manually seeds the PRNG
X509_to_X509_REQ NULL pointer deref (CVE-2015-0288)
OpenVPN, nor the OpenSSL ssl functions call X509_to_X509_REQ()

Mitigating factors

Use of TLS auth keys offers good protection against these vulnerabilities.