Ubuntu Security Notice 2368-1 - It was discovered that OpenVPN incorrectly handled HMAC comparisons when running in UDP mode. If a remote attacker were able to perform a man-in-the-middle attack, this flaw could possibly be used to perform a plaintext recovery attack.
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Gentoo Linux Security Advisory 201311-13 - Multiple vulnerabilities have been found in OpenVPN, allowing remote attackers to read encrypted traffic. Versions less than 2.3.1 are affected.
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Mandriva Linux Security Advisory 2013-167 - OpenVPN 2.3.0 and earlier running in UDP mode are subject to chosen ciphertext injection due to a non-constant-time HMAC comparison function. Plaintext recovery may be possible using a padding oracle attack on the CBC mode cipher implementation of the crypto library, optimistically at a rate of about one character per 3 hours. PolarSSL seems vulnerable to such an attack; the vulnerability of OpenSSL has not been verified or tested.
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