rust-openssl is a set of OpenSSL bindings for the Rust programming language. In affected versions ssl::select_next_proto can return a slice pointing into the server argument's buffer but with a lifetime bound to the client argument. In situations where the sever buffer's lifetime is shorter than the client buffer's, this can cause a use after free. This could cause the server to crash or to return arbitrary memory contents to the client. The crateopenssl version 0.10.70 fixes the signature of ssl::select_next_proto to properly constrain the output buffer's lifetime to that of both input buffers. Users are advised to upgrade. In standard usage of ssl::select_next_proto in the callback passed to SslContextBuilder::set_alpn_select_callback, code is only affected if the server buffer is constructed within the callback.