There's a new alpha release available for download. If you build Tor from source, you can download the source code for 0.4.5.2-alpha from the download page on the website. Packages should be available over the coming weeks, with a new alpha Tor Browser release by mid-December.

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

Tor 0.4.5.2-alpha is the second alpha release in the 0.4.5.x series. It fixes several bugs present in earlier releases, including one that made it impractical to run relays on Windows. It also adds a few small safety features to improve Tor's behavior in the presence of strange compile-time options, misbehaving proxies, and future versions of OpenSSL.

Changes in version 0.4.5.2-alpha - 2020-11-23

• Major bugfixes (relay, windows):
  • Fix a bug in our implementation of condition variables on Windows. Previously, a relay on Windows would use 100% CPU after running for some time. Because of this change, Tor now require Windows Vista or later to build and run. Fixes bug 30187; bugfix on 0.2.6.3-alpha. (This bug became more serious in 0.3.1.1-alpha with the introduction of consensus diffs.) Patch by Daniel Pinto.
• Minor features (compilation):
  • Disable deprecation warnings when building with OpenSSL 3.0.0 or later. There are a number of APIs newly deprecated in OpenSSL 3.0.0 that Tor still requires. (A later version of Tor will try to stop depending on these APIs.) Closes ticket 40165.

There's a new alpha release available for download. If you build Tor from source, you can download the source code for Tor 0.4.5.1-alpha from the download page on the website. Packages should be available over the coming weeks, with a new alpha Tor Browser release some time this month, assuming we get #40172 figured out.

Remember, this is an alpha release: you should only run this if you'd like to find and report more bugs than usual. We'll be trying to put out putting out stable backport releases in the next week or so.

Tor 0.4.5.1-alpha is the first alpha release in the 0.4.5.x series. It improves support for IPv6, address discovery and self-testing, code metrics and tracing.

This release also fixes TROVE-2020-005, a security issue that could be used, under certain cases, by an adversary to observe traffic patterns on a limited number of circuits intended for a different relay. To mount this attack, the adversary would need to actively extend circuits to an incorrect address, as well as compromise a relay's legacy RSA-1024 key. We'll be backporting this fix to other release series soon, after it has had some testing.

Here are the changes since 0.4.4.5.

Changes in version 0.4.5.1-alpha - 2020-11-01

• Major features (build):
  • When building Tor, first link all object files into a single static library. This may help with embedding Tor in other programs. Note that most Tor functions do not constitute a part of a stable or supported API: only those functions in tor_api.h should be used if embedding Tor. Closes ticket 40127.
• Major features (metrics):
  • Introduce a new MetricsPort which exposes, through an HTTP interface, a series of metrics that tor collects at runtime. At the moment, the only supported output format is Prometheus data model. Closes ticket 40063. See the manual page for more information and security considerations.

There's a new alpha release available for download. If you build Tor from source, you can download the source code for 0.4.4.3-alpha from the download page on the website. Packages should be available over the coming weeks, with a new alpha Tor Browser release by mid-August.

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

Tor 0.4.4.3-alpha fixes several annoyances in previous versions, including one affecting NSS users, and several affecting the Linux seccomp2 sandbox.

Changes in version 0.4.4.3-alpha - 2020-07-27

• Major features (fallback directory list):
  • Replace the 148 fallback directories originally included in Tor 0.4.1.4-rc (of which around 105 are still functional) with a list of 144 fallbacks generated in July 2020. Closes ticket 40061.
• Major bugfixes (NSS):
  • When running with NSS enabled, make sure that NSS knows to expect nonblocking sockets. Previously, we set our TCP sockets as nonblocking, but did not tell NSS, which in turn could lead to unexpected blocking behavior. Fixes bug 40035; bugfix on 0.3.5.1-alpha.

There's a new alpha release available for download. If you build Tor from source, you can download the source code for 0.4.4.1-alpha from the download page. Packages should be available over the coming weeks, with a new alpha Tor Browser release by early July.

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 0.4.4.x series. It improves our guard selection algorithms, improves the amount of code that can be disabled when running without relay support, and includes numerous small bugfixes and enhancements. It also lays the ground for some IPv6 features that we'll be developing more in the next (0.4.5) series.

Here are the changes since 0.4.3.5.

Changes in version 0.4.4.1-alpha - 2020-06-16

• Major features (Proposal 310, performance + security):
  • Implements Proposal 310, "Bandaid on guard selection". Proposal 310 solves load-balancing issues with older versions of the guard selection algorithm, and improves its security. Under this new algorithm, a newly selected guard never becomes Primary unless all previously sampled guards are unreachable. Implements recommendation from 32088. (Proposal 310 is linked to the CLAPS project researching optimal client location-aware path selections. This project is a collaboration between the UCLouvain Crypto Group, the U.S. Naval Research Laboratory, and Princeton University.)
• Major features (IPv6, relay):
  • Consider IPv6-only EXTEND2 cells valid on relays. Log a protocol warning if the IPv4 or IPv6 address is an internal address, and internal addresses are not allowed. But continue to use the other address, if it is valid. Closes ticket 33817.
  • If a relay can extend over IPv4 and IPv6, and both addresses are provided, it chooses between them uniformly at random. Closes ticket 33817.
  • Re-use existing IPv6 connections for circuit extends. Closes ticket 33817.
  • Relays may extend circuits over IPv6, if the relay has an IPv6 ORPort, and the client supplies the other relay's IPv6 ORPort in the EXTEND2 cell. IPv6 extends will be used by the relay IPv6 ORPort self-tests in 33222. Closes ticket 33817.

There's a new alpha release available for download. If you build Tor from source, you can download the source code for 0.4.3.3-alpha from the download page on the website. Packages should be available over the coming days, including a new alpha Tor Browser.

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

Tor 0.4.3.3-alpha fixes several bugs in previous releases, including TROVE-2020-002, a major denial-of-service vulnerability that affected all released Tor instances since 0.2.1.5-alpha. Using this vulnerability, an attacker could cause Tor instances to consume a huge amount of CPU, disrupting their operations for several seconds or minutes. This attack could be launched by anybody against a relay, or by a directory cache against any client that had connected to it. The attacker could launch this attack as much as they wanted, thereby disrupting service or creating patterns that could aid in traffic analysis. This issue was found by OSS-Fuzz, and is also tracked as CVE-2020-10592.

We do not have reason to believe that this attack is currently being exploited in the wild, but nonetheless we advise everyone to upgrade as soon as packages are available.

There are also new stable releases coming out today; I'll describe them in an upcoming post.

Changes in version 0.4.3.3-alpha - 2020-03-18

• Major bugfixes (security, denial-of-service):
  • Fix a denial-of-service bug that could be used by anyone to consume a bunch of CPU on any Tor relay or authority, or by directories to consume a bunch of CPU on clients or hidden services. Because of the potential for CPU consumption to introduce observable timing patterns, we are treating this as a high-severity security issue. Fixes bug 33119; bugfix on 0.2.1.5-alpha. Found by OSS-Fuzz. We are also tracking this issue as TROVE-2020-002 and CVE-2020-10592.
• Major bugfixes (circuit padding, memory leak):
  • Avoid a remotely triggered memory leak in the case that a circuit padding machine is somehow negotiated twice on the same circuit. Fixes bug 33619; bugfix on 0.4.0.1-alpha. Found by Tobias Pulls. This is also tracked as TROVE-2020-004 and CVE-2020-10593.

There's a new alpha release available for download. If you build Tor from source, you can download the source code for 0.4.3.2-alpha from the download page on the website. Packages should be available over the coming weeks, with a new alpha Tor Browser release likely in the coming week.

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 second stable alpha release in the Tor 0.4.3.x series. It fixes several bugs present in the previous alpha release. Anybody running the previous alpha should upgrade and look for bugs in this one instead.

Changes in version 0.4.3.2-alpha - 2020-02-10

• Major bugfixes (onion service client, authorization):
  • On a NEWNYM signal, purge entries from the ephemeral client authorization cache. The permanent ones are kept. Fixes bug 33139; bugfix on 0.4.3.1-alpha.
• Minor features (best practices tracker):
  • Practracker now supports a --regen-overbroad option to regenerate the exceptions file, but only to revise exceptions to be _less_ tolerant of best-practices violations. Closes ticket 32372.

This is the first alpha release in the 0.4.3.x series. It includes improved support for application integration of onion services, support for building in a client-only mode, and newly improved internal documentation (online at https://src-ref.docs.torproject.org/tor/). It also has numerous other small bugfixes and features, as well as improvements to our code's internal organization that should help us write better code in the future.

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

There's a new alpha release available for download. If you build Tor from source, you can download the source code for 0.4.2.2-alpha from the download page on the website. Packages should be available over the coming weeks, with a new alpha Tor Browser release likely 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 release fixes several bugs from the previous alpha release, and from earlier versions. It also includes a change in authorities, so that they begin to reject the currently unsupported release series.

Changes in version 0.4.2.2-alpha - 2019-10-07

• Major features (directory authorities):
  • Directory authorities now reject relays running all currently deprecated release series. The currently supported release series are: 0.2.9, 0.3.5, 0.4.0, 0.4.1, and 0.4.2. Closes ticket 31549.
• Major bugfixes (embedded Tor):
  • Avoid a possible crash when restarting Tor in embedded mode and enabling a different set of publish/subscribe messages. Fixes bug 31898; bugfix on 0.4.1.1-alpha.

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.