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August 13, 2018 20:57

The Vanguards Onion Service Addon

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Even after deployment of the new v3 onion service protocol, the attacks facing onion services are wide-ranging, and still require more extensive modifications to fix in Tor-core itself.

Because of this, we have decided to rapid-prototype these defenses in a controller addon in order to make them available ahead of their official Tor-core release, for onion services that require high security as soon as possible.

For details about the defenses themselves, please see

For additional security information, please see

Installation Methods

There are several ways to use this addon.

Packages for debian-like systems exist, but they are typically out of date. Check backports, if you're lucky it might get updated there.

If you are using this addon with a system tor, and not using a system vanguards package, you will need to run the following as the system Tor user, because this addon needs access to Tor's data directory. To do this on debian-like systems, do:

  sudo -u debian-tor bash

Then, run all of the following as the debian-tor user.

Running this addon directly from git

This is the safest option to use, since it avoids having pip and/or virtualenv download packages from PYPI without verification.

  1. Retrieve this repository and optionally verify a signed git version tag.
  2. Install Stem
  3. Run ./src/

By default, vanguards will try to connect to "/run/tor/control", and if that fails, will try control port 9051 (System Tor), and then 9151 (Tor Browser).

If your control port is on an alternate IP and Port, specify that with --control_host IP --control_port portnum.

If you are using a different control socket path, specify its full path with --control_socket /path/to/socket.

Note that ./src/ has several other options under --help.

Using VirtualEnv

This option tells virtualenv not to download packages, and only downloads pip packages with --require-hashes. It should be safe.

To install Stem and Vanguards into their own python virtualenv, run:

torsocks ./
source vanguardenv/bin/activate

If you do not want your environment to be in the vanguardenv subdirectory, you can specify a different directory as an argument to


This project is also listed on the Python Package Index. To install the latest release via pip without any verification, do:

torsocks pip install vanguards

If your distribution provides pypy3 (see Performance Tuning), you can do:

torsocks pypy3 -m pip install vanguards

How to use the addon


All of the subsystems of this addon can be tuned via a configuration file. Check out this documented example configuration file for more information.

Configuration files can be specified on the command line. The default is to read vanguards.conf from the current working directory. If the environment variable $VANGUARDS_CONFIG is set, the config file will be read from the file specified in that variable.

Onion service use

This addon is primarily intended for onion service operators. To use it, set up your onion service to expose a control port listener using the ControlPort or ControlSocket torrc directives:

ControlPort 9099             # or ControlSocket /path/to/socket
CookieAuthentication 1
DataDirectory /path/to/tor/datadir

and then run:

vanguards --control_port 9099     # (or --control_socket /path/to/socket).

Client use

It is also possible to use the vanguards addon as a regular Tor client with Tor Browser or with Onionshare.

To use it with Tor Browser, all you have to do is start Tor Browser, and then run:


If you also have a system Tor, you will need to specify Tor Browser's control port with --control_port 9151

To use it with Onionshare, set up your Tor to expose a control port and attach both onionshare and the vanguards addon to it.

Performance Tuning

For very high traffic onion services, we recommend using PyPy instead of CPython. PyPy contains a JIT that should make this addon run considerably faster.

The easiest way to use PyPy is to do sudo apt-get install pypy3 or equivalent before running ./ as per above. The script will then see that pypy is installed, and use it by default in the resulting virtualenv.

To switch to pypy after running, simply remove the vanguardenv directory and run again.

If you want to use pypy outside of a virtualenv, install Stem 1.7.0 or later on your system, and then run the addon directly from the source tree with:

  pypy3 ./src/

Additionally, you can try running vanguards components in parallel, so that the system does not bottleneck on one CPU core. A simple test script called is available to try this. If it helps, please let us know!

Vanguards by itself should not require much overhead, but if even that is too much, you can run the following once per hour from cron to update your torrc with fresh layer2 and layer3 guards:

  ./src/ --one_shot_vanguards

What do the logs mean?

This is an experimental addon with many heuristics that still need tuning. Events that represent severe issues are at WARN level. You should react to these events.

Warns are currently emitted for the following conditions:

  1. When your service is disconnected from the Tor network, we WARN. Downtime can be a side channel signal or a passive information leak, and you should ensure your Internet connection is reliable to minimize downtime of your service as much as possible.
  2. When a hidden service descriptor circuit sends more than 30KB, we WARN. If this happens, it is either a bug, a heavily-modified hidden service descriptor, or an actual attack.
  3. When you set ExcludeNodes in Tor to exclude countries, but do not give Tor a GeoIP file, we WARN.
  4. If you disable killing circuits in the rendguard component, we WARN when use counts for rends are exceeded.
  5. We WARN upon receipt of any cell that the Tor client drops or ignores.
  6. If you enable introduction circuit rate limiting, a WARN is emitted when introduction circuits are killed.

Events that are detected by heuristics that still need tuning are at NOTICE level. They may be a bug, a false positive, or an actual attack. If in doubt, don't panic. Please check the Github issues to see if any known false positives are related to these lines, and if not, consider filing an issue. Please redact any relay fingerprints from the messages before posting.

What else should I read?

For technical details about the defenses that this addon provides, please see

For additional security information, please see