There's a new alpha release available for download. If you build Tor from source, you can download the source code for 0.4.2.1-alpha from the download page on the website. Packages should be available over the coming weeks, with a new alpha Tor Browser release in the next couple of weeks.

Remember, this is an alpha release: you should only run this if you'd like to find and report more bugs than usual.

This is the first alpha release in the 0.4.2.x series. It adds new defenses for denial-of-service attacks against onion services. It also includes numerous kinds of bugfixes and refactoring to help improve Tor's stability and ease of development.

Changes in version 0.4.2.1-alpha - 2019-09-17

Major features (onion service v3, denial of service): Add onion service introduction denial of service defenses. Intro points can now rate-limit client introduction requests, using parameters that can be sent by the service within the ESTABLISH_INTRO cell. If the cell extension for this is not used, the intro point will honor the consensus parameters. Closes ticket 30924.

Major bugfixes (circuit build, guard): When considering upgrading circuits from "waiting for guard" to "open", always ignore circuits that are marked for close. Previously we could end up in the situation where a subsystem is notified of a circuit opening, but the circuit is still marked for close, leading to undesirable behavior. Fixes bug 30871; bugfix on 0.3.0.1-alpha.

