Fix TROVE-2017-010: Remote DoS attack against directory authorities

TROVE-2017-010: Remote DoS attack against directory authorities

SEVERITY: Medium

ALSO TRACKED AS: CVE-2017-8820

SUMMARY:

  If an attacker uploads a malformed descriptor to a directory
  authority, lacking a protocol line and not claiming any particular
  Tor compatibility, the authority will crash when it tries to vote.

THE PROBLEM:

  An attacker who sends a malformatted descriptor to a directory
  authority can make that directory authority crash by reading a null
  pointer.

  The problematic code was introduced in 0.2.9.4-alpha, with the rest
  of the subprotocols system.

FIX:

  All directory authorities should upgrade to one of the releases with
  a fix for this issue: 0.2.9.14, 0.3.0.13, 0.3.1.9, or 0.3.2.6-alpha.