OpenVPN, when using a 64-bit block cipher, makes it easier for remote attackers to obtain cleartext data via a birthday attack against a long-duration encrypted session, as demonstrated by an HTTP-over-OpenVPN session using Blowfish in CBC mode, aka a "Sweet32" attack.
OpenVPN, cuando utiliza un cifrado de bloques de 64 bits, facilita a atacantes remotos obtener datos de texto plano a través de un ataque birthday contra una sesión encriptada de larga duración, como lo demuestra una sesión HTTP-over-OpenVPN usando Blowfish en modo CBC, también conocido como ataque "Sweet32".
Karthikeyan Bhargavan and Gaetan Leurent discovered that 64-bit block ciphers are vulnerable to a birthday attack. A remote attacker could possibly use this issue to recover cleartext data. Fixing this issue requires a configuration change to switch to a different cipher. This update adds a warning to the log file when a 64-bit block cipher is in use. This issue only affected Ubuntu 14.04 LTS, Ubuntu 16.04 LTS and Ubuntu 16.10. It was discovered that OpenVPN incorrectly handled rollover of packet ids. An authenticated remote attacker could use this issue to cause OpenVPN to crash, resulting in a denial of service. This issue only affected Ubuntu 14.04 LTS, Ubuntu 16.04 LTS and Ubuntu 16.10. Various other issues were also addressed.
