[tor-announce] New stable security release: Tor

Alexander Færøy ahf at torproject.org
Mon Aug 16 20:58:16 UTC 2021

Hello, everyone!

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Source code for Tor is now available; you can download the
source code from the download page at
https://www.torproject.org/download/tor/. Packages should be available
within the next several weeks, with a new Tor Browser later this week.

Changes in version - 2021-08-16
  This version fixes several bugs from earlier versions of Tor, including one
  that could lead to a denial-of-service attack. Everyone running an earlier
  version, whether as a client, a relay, or an onion service, should upgrade
  to Tor,, or

  o Major bugfixes (cryptography, security):
    - Resolve an assertion failure caused by a behavior mismatch between our
      batch-signature verification code and our single-signature verification
      code. This assertion failure could be triggered remotely, leading to a
      denial of service attack. We fix this issue by disabling batch
      verification. Fixes bug 40078; bugfix on This issue is
      also tracked as TROVE-2021-007 and CVE-2021-38385. Found by Henry de

  o Minor feature (fallbackdir):
    - Regenerate fallback directories list. Close ticket 40447.

  o Minor features (geoip data):
    - Update the geoip files to match the IPFire Location Database,
      as retrieved on 2021/08/12.

  o Minor bugfix (crypto):
    - Disable the unused batch verification feature of ed25519-donna. Fixes
      bug 40078; bugfix on Found by Henry de Valence.

  o Minor bugfixes (onion service):
    - Send back the extended SOCKS error 0xF6 (Onion Service Invalid Address)
      for a v2 onion address. Fixes bug 40421; bugfix on

  o Minor bugfixes (relay):
    - Reduce the compression level for data streaming from HIGH to LOW in
      order to reduce CPU load on the directory relays. Fixes bug 40301;
      bugfix on

  o Minor bugfixes (timekeeping):
    - Calculate the time of day correctly on systems where the time_t
      type includes leap seconds. (This is not the case on most
      operating systems, but on those where it occurs, our tor_timegm
      function did not correctly invert the system's gmtime function,
      which could result in assertion failures when calculating
      voting schedules.)  Fixes bug 40383; bugfix on

Alexander Færøy

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