In !May/June 2017 Guido Vranken threw a fuzzer at OpenVPN 2.4.2. In the process he found several vulnerabilities and reported them to the OpenVPN project. The OpenVPN Git branches were patches as follows:

* master: 7 patches

**PLEASE NOTE** We have noticed that the Cloudflare front have been serving out the wrong contents for several users. See [this page](/release-packages-2.4.3-2.3.17) for more information.

This vulnerability is of serious nature: it can be used to remotely shutdown an openvpn server or client if IPv6 and --mssfix are enabled and the IPv6 networks used inside the VPN are known.

* master: c3f47077a7

If clients use a HTTP proxy with NTLM authentication (i.e. "--http-proxy <server> <port> [<authfile>|'auto'|'auto-nct'] ntlm2"),

If the proxy password is not reused, this is unlikely to compromise the security of the OpenVPN tunnel itself. Clients who do not use the --http-proxy option with ntlm2 authentication are not affected.

* master: 7718c8984f

OpenVPN did not check the return value of ASN1_STRING_to_UTF8() in extract_x509_extension(). Ignoring such a failure could result in buf being free'd twice. An error in ASN1_STRING_to_UTF8() can be caused remotely if the peer can make the local process run out of memory.

The problem can only be triggered for configurations that use the --x509-alt-username option with an x509 extension (i.e. the option parameter starts with "ext:"). Extensive testing by Guido Vranken gives confidence that this function is very unlikely to fail in real-world usage (using subjectAltName or issuerAltName extensions) for other reasons than memory exhaustion.

* master: cb4e35ece4

Several of our OpenSSL-specific certificate-parsing code paths did not always clear all allocated memory. Since a client can cause a few bytes of memory to be leaked for each connection attempt, a client can cause a server to run out of memory and thereby kill the server. That makes this a (quite inefficient) DoS attack.

In particular when using the --x509-alt-username option on openssl builds with an extension (argument prefixed with "ext:", e.g. "ext:subjectAltName"), the code would not free all allocated memory.

* master: 2d032c7fcd

asn1_buf_to_c_string() returned a literal string if the input ASN.1 string contained a NUL character, while the caller expects a mutable string. The caller will attempt to change this string, which allows a client to crash a server by sending a certificate with an embedded NUL character.

* applies to mbedtls builds only

* master: 426392940c

Client could crashes if the peer did not specify the 'realm' and/or 'nonce' values. These pointers are dereferenced in DigestCalcHA1() and DigestCalcResponse(); hence, if not set, a null-pointer dereference would occur.

* master: 14865773ad

Many of the findings were such that they don't have a practical security impact. Nevertheless they are bugs and were fixed in the following Git commits:

* Restrict --x509-alt-username extension types