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SNI Proxy

Proxies incoming HTTP and TLS connections based on the hostname contained in the initial request of the TCP session. This enables HTTPS name-based virtual hosting to separate backend servers without installing the private key on the proxy machine.

Status: Deprecated

2023-12-13

When I started this project, there wasn't another proxy that filled this niche. Now, there are many proxies available to proxy layer-4 based on the TLS SNI extension, including Nginx. Additionally, web traffic is evolving: with HTTP/2, multiple hostnames can be multiplexed in a single TCP stream preventing SNI Proxy from routing it correctly based on hostname, and HTTP/3 (QUIC) uses UDP transport. SNI Proxy just doesn't support these protocols, and adding support for them would complicate it significantly. For these reasons, I'm transitioning SNI Proxy to a deprecated status.

Honestly, this has been the case for last several years, and I hadn't published anything to that affect. With CVE-2023-25076 it became clear that this situation needs to be communicated clearly.

In some cases, SNI Proxy might be a better fit than a more general purpose proxy, so I'm not going to abandon the project completely. I'll still monitor issues and email requests; however, unless it is a significant security or reliablity issue, don't expect a response.

Features

  • Name-based proxying of HTTPS without decrypting traffic. No keys or certificates required.
  • Supports both TLS and HTTP protocols.
  • Supports IPv4, IPv6 and Unix domain sockets for both back-end servers and listeners.
  • Supports multiple listening sockets per instance.
  • Supports HAProxy proxy protocol to propagate original source address to back-end servers.

Usage

Usage: sniproxy [-c <config>] [-f] [-n <max file descriptor limit>] [-V]
    -c  configuration file, defaults to /etc/sniproxy.conf
    -f  run in foreground, do not drop privileges
    -n  specify file descriptor limit
    -V  print the version of SNIProxy and exit

Installation

For Debian or Fedora based Linux distributions see building packages below.

Prerequisites

  • Autotools (autoconf, automake, gettext and libtool)
  • libev4, libpcre2 (or libpcre) and libudns development headers
  • Perl and cURL for test suite

Install

./autogen.sh && ./checonfigure --enable-dns && make check && sudo make install

Building Debian/Ubuntu package

This is the preferred installation method on recent Debian based distributions:

  1. Install required packages

     sudo apt-get install autotools-dev cdbs debhelper dh-autoreconf dpkg-dev gettext libev-dev libpcre2-dev libudns-dev pkg-config fakeroot devscripts

  2. Build a Debian package

     ./autogen.sh && dpkg-buildpackage

  3. Install the resulting package

     sudo dpkg -i ../sniproxy_<version>_<arch>.deb

Building Fedora/RedHat package

This is the preferred installation method for modern Fedora based distributions.

  1. Install required packages

     sudo yum install autoconf automake curl gettext-devel libev-devel pcre-devel perl pkgconfig rpm-build udns-devel

  2. Build a distribution tarball:

     ./autogen.sh && ./configure --enable-dns && make dist

  3. Build a RPM package

     rpmbuild --define "_sourcedir `pwd`" -ba redhat/sniproxy.spec

  4. Install resulting RPM

     sudo yum install ../sniproxy-<version>.<arch>.rpm

I've used Scientific Linux 6 a fair amount, but I prefer Debian based distributions. RPM builds are tested in Travis-CI on Ubuntu, but not natively. This build process may not follow the current Fedora packaging standards, and may not even work.

Building on OS X with Homebrew

  1. install dependencies.

     brew install libev pcre udns autoconf automake gettext libtool

  2. Read the warning about gettext and force link it so autogen.sh works. We need the GNU gettext for the macro AC_LIB_HAVE_LINKFLAGS which isn't present in the default OS X package.

     brew link --force gettext

  3. Make it so

     ./autogen.sh && ./configure --enable-dns && make

OS X support is a best effort, and isn't a primary target platform.

Configuration Syntax

user daemon

pidfile /tmp/sniproxy.pid

error_log {
    syslog daemon
    priority notice
}

listener 127.0.0.1:443 {
    protocol tls
    table TableName

    # Specify a server to use if the initial client request doesn't contain
    # a hostname
    fallback 192.0.2.5:443
}

table TableName {
    # Match exact request hostnames
    example.com 192.0.2.10:4343
    # If port is not specified the listener port will be used
    example.net [2001:DB8::1:10]
    # Or use regular expression to match
    .*\\.com    [2001:DB8::1:11]:443
    # Combining regular expression and wildcard will resolve the hostname
    # client requested and proxy to it
    .*\\.edu    *:443
}

DNS Resolution

Using hostnames or wildcard entries in the configuration requires sniproxy to be built with UDNS. SNIProxy will still build without UDNS, but these features will be unavailable.

UDNS uses a single UDP socket for all queries, so it is recommended you use a local caching DNS resolver (with a single socket each DNS query is protected by spoofing by a single 16 bit query ID, which makes it relatively easy to spoof).