CVE-2017-7520

OpenVPN versions before 2.4.3 and before 2.3.17 are vulnerable to denial-of-service and/or possibly sensitive memory leak triggered by man-in-the-middle attacker.

It was possible to trigger an assertion by sending a malformed IPv6 packet. That issue could have been abused to remotely shutdown an openvpn server or client, if IPv6 and --mssfix were enabled and if the IPv6 networks used inside the VPN were known (CVE-2017-7508).

Some parts of the certificate-parsing code did not always clear all allocated memory. This would have allowed clients to leak a few bytes of memory for each connection attempt, thereby facilitating a (quite inefficient) DoS attack on the server (CVE-2017-7512).

If clients used a HTTP proxy with NTLM authentication, a man-in-the-middle attacker between client and proxy could cause the client to crash or disclose at most 96 bytes of stack memory. The disclosed stack memory was likely to contain the proxy password. If the proxy password had not been reused, this was unlikely to compromise the security of the OpenVPN tunnel itself. Clients who did not use the --http-proxy option with ntlm2 authentication were not affected (CVE-2017-7520).

The ASN1 parsing code contained a bug that could have resulted in some buffers being free()d twice, and this issue could have potentially been triggered remotely by a VPN peer (CVE-2017-7521).

This update for openvpn fixes the following issues:

• Some parts of the certificate-parsing code did not always clear all allocated memory. This would have allowed clients to leak a few bytes of memory for each connection attempt, thereby facilitating a (quite inefficient) DoS attack on the server. [bsc#1044947, CVE-2017-7521]

• The ASN1 parsing code contained a bug that could have resulted in some buffers being free()d twice, and this issue could have potentially been triggered remotely by a VPN peer. [bsc#1044947, CVE-2017-7521]

• If clients used a HTTP proxy with NTLM authentication, a man-in-the-middle attacker between client and proxy could cause the client to crash or disclose at most 96 bytes of stack memory. The disclosed stack memory was likely to contain the proxy password. If the proxy password had not been reused, this was unlikely to compromise the security of the OpenVPN tunnel itself. Clients who did not use the --http-proxy option with ntlm2 authentication were not affected. [bsc#1044947, CVE-2017-7520]

• It was possible to trigger an assertion by sending a malformed IPv6 packet. That issue could have been abused to remotely shutdown an openvpn server or client, if IPv6 and --mssfix were enabled and if the IPv6 networks used inside the VPN were known. [bsc#1044947, CVE-2017-7508]

This update for openvpn-openssl1 fixes the following issues:

• Some parts of the certificate-parsing code did not always clear all allocated memory. This would have allowed clients to leak a few bytes of memory for each connection attempt, thereby facilitating a (quite inefficient) DoS attack on the server. [bsc#1044947, CVE-2017-7521]

• The ASN1 parsing code contained a bug that could have resulted in some buffers being free()d twice, and this issue could have potentially been triggered remotely by a VPN peer. [bsc#1044947, CVE-2017-7521]

• If clients used a HTTP proxy with NTLM authentication, a man-in-the-middle attacker between client and proxy could cause the client to crash or disclose at most 96 bytes of stack memory. The disclosed stack memory was likely to contain the proxy password. If the proxy password had not been reused, this was unlikely to compromise the security of the OpenVPN tunnel itself. Clients who did not use the --http-proxy option with ntlm2 authentication were not affected. [bsc#1044947, CVE-2017-7520]

• It was possible to trigger an assertion by sending a malformed IPv6 packet. That issue could have been abused to remotely shutdown an openvpn server or client, if IPv6 and --mssfix were enabled and if the IPv6 networks used inside the VPN were known. [bsc#1044947, CVE-2017-7508]

• The installed sample configuration file was updated to comply to FIPS requirements. [bsc#988522]

• Remedy large latencies on the openVPN server during authentication process. [bsc#959511]

• Fix potential denial-of-service attacks found during independent audits. [bsc#1038713, bsc#1038709, CVE-2017-7478, bsc#1038711, CVE-2017-7479]

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)