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188 lines
8.9 KiB
Markdown
# SSLproxy - transparent SSL/TLS proxy for decrypting and diverting network traffic to other programs for deep SSL inspection [](https://travis-ci.org/sonertari/SSLproxy)
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Copyright (C) 2017-2018, [Soner Tari](http://comixwall.org).
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https://github.com/sonertari/SSLproxy
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Copyright (C) 2009-2018, [Daniel Roethlisberger](//daniel.roe.ch/).
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https://www.roe.ch/SSLsplit
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## Overview
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SSLproxy is a proxy for SSL/TLS encrypted network connections. It is intended
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to be used for decrypting and diverting network traffic to other programs, such
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as UTM services, for deep SSL inspection. See [this
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presentation](https://drive.google.com/open?id=12YaGIGs0-xfpqMNAY3rzUbIyed-Tso8W)
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for a summary.
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SSLproxy is designed to transparently terminate connections that are redirected
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to it using a network address translation engine. SSLproxy then terminates
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SSL/TLS and initiates a new SSL/TLS connection to the original destination
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address. Packets received on the client side are decrypted and sent to the
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program listening on a port given in the proxy specification. SSLproxy inserts
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in the first packet the address and port it is expecting to receive the packets
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back from the program. Upon receiving the packets back, SSLproxy re-encrypts
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and sends them to their original destination. The return traffic follows the
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same path back to the client in reverse order.
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This is similar in principle to [divert
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sockets](https://man.openbsd.org/divert.4), where the packet filter diverts the
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packets to a program listening on a divert socket, and after processing the
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packets the program reinjects them into the kernel. If there is no program
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listening on that divert socket or the program does not reinject the packets
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into the kernel, the connection is effectively blocked. In the case of
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SSLproxy, SSLproxy acts as both the packet filter and the kernel, and the
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communication occurs over networking sockets.
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For example, given the following proxy specification:
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https 127.0.0.1 8443 up:8080
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The SSLproxy listens for HTTPS connections on 127.0.0.1:8443. Upon receiving a
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connection from the Client, it decrypts and diverts the packets to a Program
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listening on 127.0.0.1:8080. After processing the packets, the Program gives
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them back to the SSLproxy listening on a dynamically assigned address, which
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the Program obtains from the first packet in the connection. Then the SSLproxy
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re-encrypts and sends the packets to the Server. The response from the Server
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follows the same path to the Client in reverse order.
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The program that packets are diverted to should support this mode of operation.
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Specifically, it should be able to recognize the SSLproxy address in the first
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packet, and give the first and subsequent packets back to the SSLproxy
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listening on that address, instead of sending them to the original destination
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as it normally would.
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A sample line SSLproxy inserts into the first packet in the connection is the
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following:
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SSLproxy: [127.0.0.1]:34649,[192.168.3.24]:47286,[192.168.111.130]:443,s
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The first IP:port pair is a dynamically assigned address that the SSLproxy
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expects the program send the packets back to it. The second and third IP:port
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pairs are the actual source and destination addresses of the connection
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respectively. Since the program receives the packets from the SSLproxy, it
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cannot determine the source and destination addresses of the packets by
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itself, hence must rely on the information in this SSLproxy line. The last
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letter is either s or p, for SSL/TLS encrypted or plain traffic respectively.
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This information is also important for the program, because it cannot reliably
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determine if the actual network traffic it is processing was encrypted or not.
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SSLproxy supports plain TCP, plain SSL, HTTP, HTTPS, POP3, POP3S, SMTP, and
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SMTPS connections over both IPv4 and IPv6. It also has the ability to
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dynamically upgrade plain TCP to SSL in order to generically support SMTP
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STARTTLS and similar upgrade mechanisms. SSLproxy fully supports Server Name
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Indication (SNI) and is able to work with RSA, DSA and ECDSA keys and DHE and
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ECDHE cipher suites. Depending on the version of OpenSSL, SSLproxy supports
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SSL 3.0, TLS 1.0, TLS 1.1 and TLS 1.2, and optionally SSL 2.0 as well.
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For SSL and HTTPS connections, SSLproxy generates and signs forged X509v3
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certificates on-the-fly, mimicking the original server certificate's subject
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DN, subjectAltName extension and other characteristics. SSLproxy has the
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ability to use existing certificates of which the private key is available,
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instead of generating forged ones. SSLproxy supports NULL-prefix CN
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certificates but otherwise does not implement exploits against specific
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certificate verification vulnerabilities in SSL/TLS stacks.
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SSLproxy implements a number of defences against mechanisms which would
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normally prevent MitM attacks or make them more difficult. SSLproxy can deny
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OCSP requests in a generic way. For HTTP and HTTPS connections, SSLproxy
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mangles headers to prevent server-instructed public key pinning (HPKP), avoid
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strict transport security restrictions (HSTS), avoid Certificate Transparency
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enforcement (Expect-CT) and prevent switching to QUIC/SPDY, HTTP/2 or
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WebSockets (Upgrade, Alternate Protocols). HTTP compression, encodings and
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keep-alive are disabled to make the logs more readable.
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Another reason to disable persistent connections is to reduce file descriptor
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usage. Accordingly, connections are closed if they remain idle for a certain
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period of time. The default timeout is 120 seconds, which can be changed in a
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configuration file.
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SSLproxy verifies upstream certificates by default. If the verification fails,
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the connection is terminated immediately. This is in contrast to SSLsplit,
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because in order to maximize the chances that a connection can be successfully
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split, SSLsplit accepts all certificates by default, including self-signed
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ones. See [The Risks of SSL Inspection]
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(https://insights.sei.cmu.edu/cert/2015/03/the-risks-of-ssl-inspection.html)
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for the reasons of this difference.
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Logging options include traditional SSLproxy connect and content log files as
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well as PCAP files and mirroring decrypted traffic to a network interface.
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Additionally, certificates, master secrets and local process information can be
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logged.
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As SSLproxy is based on SSLsplit, this is a modified SSLsplit README file.
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See the manual page sslproxy(1) for details on using SSLproxy and setting up
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the various NAT engines.
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## Requirements
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SSLproxy depends on the OpenSSL, libevent 2.x, libpcap and libnet 1.1.x
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libraries by default; libpcap and libnet are not needed if the mirroring
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feature is omitted. The build depends on GNU make and a POSIX.2 environment in
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`PATH`. If available, pkg-config is used to locate and configure the
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dependencies. The optional unit tests depend on the check library.
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SSLproxy currently supports the following operating systems and NAT mechanisms:
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- FreeBSD: pf rdr and divert-to, ipfw fwd, ipfilter rdr
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- OpenBSD: pf rdr-to and divert-to
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- Linux: netfilter REDIRECT and TPROXY
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- Mac OS X: pf rdr and ipfw fwd
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Support for local process information (`-i`) is currently available on Mac OS X
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and FreeBSD.
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SSL/TLS features and compatibility greatly depend on the version of OpenSSL
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linked against. For optimal results, use a recent release of OpenSSL or
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LibreSSL.
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## Installation
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With the requirements above available, run:
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make
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make test # optional unit tests
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make sudotest # optional unit tests requiring privileges
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make install # optional install
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Dependencies are autoconfigured using pkg-config. If dependencies are not
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picked up and fixing `PKG_CONFIG_PATH` does not help, you can specify their
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respective locations manually by setting `OPENSSL_BASE`, `LIBEVENT_BASE`,
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`LIBPCAP_BASE`, `LIBNET_BASE` and/or `CHECK_BASE` to the respective prefixes.
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You can override the default install prefix (`/usr/local`) by setting `PREFIX`.
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For more build options and build-time defaults see [`GNUmakefile`](GNUmakefile)
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and [`defaults.h`](defaults.h).
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## Documentation
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See the manual pages `sslproxy(1)` and `sslproxy.conf(5)` for user
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documentation. See [`NEWS.md`](NEWS.md) for release notes listing significant
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changes between releases and [`SECURITY.md`](SECURITY.md) for information on
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security vulnerability disclosure.
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## License
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SSLsplit is provided under a 2-clause BSD license.
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SSLsplit contains components licensed under the MIT and APSL licenses.
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See [`LICENSE`](LICENSE), [`LICENSE.contrib`](LICENSE.contrib) and
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[`LICENSE.third`](LICENSE.third) as well as the respective source file headers
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for details.
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The modifications for SSLproxy are licensed under the same terms as SSLsplit.
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## Credits
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See [`AUTHORS.md`](AUTHORS.md) for the list of contributors.
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SSLsplit was inspired by `mitm-ssl` by Claes M. Nyberg and `sslsniff` by Moxie
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Marlinspike, but shares no source code with them.
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