Tor was updated to 0.2.4.27 to fix two security issues that could be used by an attacker to crash hidden services, or crash clients visiting hidden services. Hidden services should upgrade as soon as possible.

The following security issues were fixed:

* A malicious client could trigger an assertion failure and halt a hidden service. (CVE-2015-2928)
* A client could crash with an assertion failure when parsing a malformed hidden service descriptor. (CVE-2015-2929)

This release also backports a simple improvement to make hidden services a bit less vulnerable to denial-of-service attacks:

* Introduction points no longer allow multiple INTRODUCE1 cells to arrive on the same circuit. This should make it more expensive for attackers to overwhelm hidden services with introductions.