Ubuntu Security Notice 612-6 - USN-612-3 addressed a weakness in OpenSSL certificate and keys generation in OpenVPN by adding checks for vulnerable certificates and keys to OpenVPN. A regression was introduced in OpenVPN when using TLS and multi-client/server which caused OpenVPN to not start when using valid SSL certificates. It was also found that openssl-vulnkey from openssl-blacklist would fail when stderr was not available. This caused OpenVPN to fail to start when used with applications such as NetworkManager. A weakness has been discovered in the random number generator used by OpenSSL on Debian and Ubuntu systems. As a result of this weakness, certain encryption keys are much more common than they should be, such that an attacker could guess the key through a brute-force attack given minimal knowledge of the system. This particularly affects the use of encryption keys in OpenSSH, OpenVPN and SSL certificates. This vulnerability only affects operating systems which (like Ubuntu) are based on Debian. However, other systems can be indirectly affected if weak keys are imported into them.
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