We have new releases today. If you build Tor from source, you can download the source code for 0.4.2.7 from the download page on the website. Packages should be available within the next several days, including a new Tor Browser.

This is the third stable release in the 0.4.2.x series. It backports numerous fixes from later releases, including a fix for 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.

We're also releasing updates for our older supported series. You can find the source code for 0.3.5.10 and 0.4.1.9 from our distribution site at http://dist.torproject.org/. You can also read the 0.3.5.10 ChangeLog and the 0.4.1.9 ChangeLog.

There's also a new alpha, described in the previous blog post.

Changes in version 0.4.2.7 - 2020-03-18

Major bugfixes (security, denial-of-service, backport from 0.4.3.3-alpha): 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, backport from 0.4.3.3-alpha): 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.

