CVE-2016-6329

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.

Ciphers with 64-bit block sizes used in CBC mode were found to be vulnerable to birthday attack when key renegotiation doesn't happen frequently or at all in long running connections. Blowfish cipher as used in OpenVPN by default is vulnerable to this attack, that allows remote attacker to recover partial plaintext information (XOR of two plaintext blocks) (CVE-2016-6329).

This update for openvpn fixes the following issues:

• CVE-2016-6329: Show which ciphers should no longer be used in openvpn --show-ciphers (bsc#995374)
• CVE-2017-7478: openvpn: Authenticated user can DoS server by using a big payload in P_CONTROL (bsc#1038709)
• CVE-2017-7479: openvpn: Denial of Service due to Exhaustion of Packet-ID counter (bsc#1038711)
• Hardening measures found by internal audit (bsc#1038713)

This update for openvpn fixes the following security issues:

• CVE-2017-12166: OpenVPN was vulnerable to a buffer overflow vulnerability when key-method 1 is used, possibly resulting in code execution. (bsc#1060877).
• CVE-2016-6329: Now show which ciphers should no longer be used in openvpn --show-ciphers to avoid the SWEET32 attack (bsc#995374)
• CVE-2017-7478: OpenVPN was vulnerable to unauthenticated Denial of Service of server via received large control packet. (bsc#1038709)
• CVE-2017-7479: OpenVPN was vulnerable to reachable assertion when packet-ID counter rolls over resulting into Denial of Service of server by authenticated attacker. (bsc#1038711)
• Some other hardening fixes have also been applied (bsc#1038713)

Karthikeyan Bhargavan and Gaëtan 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. (CVE-2016-6329)

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. (CVE-2017-7479)

Guido Vranken discovered that OpenVPN incorrectly handled certain malformed IPv6 packets. A remote attacker could use this issue to cause OpenVPN to crash, resulting in a denial of service. (CVE-2017-7508)

Guido Vranken discovered that OpenVPN incorrectly handled an HTTP proxy with NTLM authentication. A remote attacker could use this issue to cause OpenVPN clients to crash, resulting in a denial of service, or possibly expose sensitive memory contents. (CVE-2017-7520)

Guido Vranken discovered that OpenVPN incorrectly handled certain x509 extensions. A remote attacker could use this issue to cause OpenVPN to crash, resulting in a denial of service. (CVE-2017-7521)