Tor 0.3.1.3-alpha is released, with a security fix for hidden services.

Hello again! This post announces the third alpha in the 0.3.1.x series, which I just released today. There were stable releases too; I'll go over them in the next post.

Tor 0.3.1.3-alpha fixes a pair of bugs that would allow an attacker to remotely crash a hidden service with an assertion failure. Anyone running a hidden service should upgrade to this version, or to some other version with fixes for TROVE-2017-004 and TROVE-2017-005.

Tor 0.3.1.3-alpha also includes fixes for several key management bugs that sometimes made relays unreliable, as well as several other bugfixes described below.

Since this is an alpha release, you can expect more bugs than usual. If you'd rather have a more stable experience, stick to the stable releases.

If you build Tor from source, you can find Tor 0.3.1.2-alpha at the usual place (at the Download page on our website). Otherwise, you'll probably want to wait until packages are available.

Changes in version 0.3.1.3-alpha - 2017-06-08

• Major bugfixes (hidden service, relay, security):
  • Fix a remotely triggerable assertion failure when a hidden service handles a malformed BEGIN cell. Fixes bug 22493, tracked as TROVE-2017-004 and as CVE-2017-0375; bugfix on 0.3.0.1-alpha.
  • Fix a remotely triggerable assertion failure caused by receiving a BEGIN_DIR cell on a hidden service rendezvous circuit. Fixes bug 22494, tracked as TROVE-2017-005 and CVE-2017-0376; bugfix on 0.2.2.1-alpha.
• Major bugfixes (relay, link handshake):
  • When performing the v3 link handshake on a TLS connection, report that we have the x509 certificate that we actually used on that connection, even if we have changed certificates since that connection was first opened. Previously, we would claim to have used our most recent x509 link certificate, which would sometimes make the link handshake fail. Fixes one case of bug 22460; bugfix on 0.2.3.6-alpha.

• Major bugfixes (relays, key management):
  • Regenerate link and authentication certificates whenever the key that signs them changes; also, regenerate link certificates whenever the signed key changes. Previously, these processes were only weakly coupled, and we relays could (for minutes to hours) wind up with an inconsistent set of keys and certificates, which other relays would not accept. Fixes two cases of bug 22460; bugfix on 0.3.0.1-alpha.
  • When sending an Ed25519 signing->link certificate in a CERTS cell, send the certificate that matches the x509 certificate that we used on the TLS connection. Previously, there was a race condition if the TLS context rotated after we began the TLS handshake but before we sent the CERTS cell. Fixes a case of bug 22460; bugfix on 0.3.0.1-alpha.
• Major bugfixes (torrc, crash):
  • Fix a crash bug when using %include in torrc. Fixes bug 22417; bugfix on 0.3.1.1-alpha. Patch by Daniel Pinto.
• Minor features (code style):
  • Add "Falls through" comments to our codebase, in order to silence GCC 7's -Wimplicit-fallthrough warnings. Patch from Andreas Stieger. Closes ticket 22446.
• Minor features (diagnostic):
  • Add logging messages to try to diagnose a rare bug that seems to generate RSA->Ed25519 cross-certificates dated in the 1970s. We think this is happening because of incorrect system clocks, but we'd like to know for certain. Diagnostic for bug 22466.
• Minor bugfixes (correctness):
  • Avoid undefined behavior when parsing IPv6 entries from the geoip6 file. Fixes bug 22490; bugfix on 0.2.4.6-alpha.
• Minor bugfixes (directory protocol):
  • Check for libzstd >= 1.1, because older versions lack the necessary streaming API. Fixes bug 22413; bugfix on 0.3.1.1-alpha.
• Minor bugfixes (link handshake):
  • Lower the lifetime of the RSA->Ed25519 cross-certificate to six months, and regenerate it when it is within one month of expiring. Previously, we had generated this certificate at startup with a ten-year lifetime, but that could lead to weird behavior when Tor was started with a grossly inaccurate clock. Mitigates bug 22466; mitigation on 0.3.0.1-alpha.
• Minor bugfixes (storage directories):
  • Always check for underflows in the cached storage directory usage. If the usage does underflow, re-calculate it. Also, avoid a separate underflow when the usage is not known. Fixes bug 22424; bugfix on 0.3.1.1-alpha.
• Minor bugfixes (unit tests):
  • The unit tests now pass on systems where localhost is misconfigured to some IPv4 address other than 127.0.0.1. Fixes bug 6298; bugfix on 0.0.9pre2.
• Documentation:
  • Clarify the manpage for the (deprecated) torify script. Closes ticket 6892.