4.17.0

Upgrade notes

Three defaults changed in this release. Read these before upgrading.

DTLS listeners are now opt-in (#2026). The server no longer starts DTLS
listeners unless --dtls is given. A deployment that relied on DTLS being up by
default will stop serving DTLS clients after the upgrade, without an error. The
deprecated --no-dtls / --no-dtls=false spellings are still accepted and now
warn.

Stateless nonce is on by default (#2036). Challenge nonces are authenticated
timestamp cookies rather than a random value stored per session, so
unauthenticated UDP requests are answered from the listener without allocating a
session. Two consequences:

• The challenge NONCE is now 24 characters instead of 16. RFC 8489 requires
  clients to treat it as an opaque string of up to 128 characters, so compliant
  clients are unaffected. --stateless-nonce=false restores the previous
  behaviour.
• The signing key is generated per process, so a restart costs each client one
  438 re-authentication round-trip, as does a retry that lands on a different
  instance behind a load balancer. Set --stateless-nonce-secret to the same
  value across a fleet to avoid both.

The default log line changed (#2031, #2033). Timestamps are ISO-8601 with
millisecond precision, the thread id is gone, the field delimiter is a single
space instead of :, and each record now occupies exactly one line. Log
shippers and any downstream parsing will need updating; the default line is now:

2026-08-02T17:32:31.297-0700 INFO Listener address to use: 127.0.0.1

--new-log-timestamp=false restores the legacy seconds-since-start counter.

Security fixes

Three fixes in this release came through the private advisory process. Advisories
are still in preparation; this section will be updated with their identifiers
once they are published.

• Allocation quotas could be bypassed under --mobility. An authenticated
  client that repeatedly created a mobility allocation and disconnected had its
  quota released while the allocation, its relay socket and its ticket stayed
  alive, letting one user hold allocations well past --user-quota /
  --total-quota until the relay port range was exhausted. The charge is now
  held until final teardown. Regression coverage:
  examples/run_tests_mobility_quota.sh.
• DTLS allocated per-peer state before the cookie was verified. A
  ClientHello from an unverified (and possibly spoofed) source caused a full
  SSL, socket and session allocation before the source had proved return
  routability. The cookie exchange is now performed statelessly via
  DTLSv1_listen(), so an unanswered ClientHello leaves no state behind. This
  completes the hardening begun in 4.16.0 (#2010, #2012, #2013).
• EVEN-PORT with the R bit clear leaked relay ports. The odd sibling port
  was reserved even when the client had not asked for it and was never released,
  so a server would eventually refuse new allocations that requested
  EVEN-PORT.

Upgrading is recommended for anyone running --mobility, DTLS, or accepting
EVEN-PORT allocations.

What's Changed

• free the secrets list on the get_user_key error paths by @alhudz in #2019
• Binding stateless fastpath by @eakraly in #2024
• Worktree stateless nonce mi fastpath by @eakraly in #2025
• Start the DTLS listeners only when --dtls is given by @eakraly in #2026
• Do not ask the kernel for an outgoing IP TTL of zero by @eakraly in #2027
• Drop --simple-log where it is a no-op alongside --log-file=stdout by @eakraly in #2028
• Remove syslog from the Docker Compose turnserver.conf by @eakraly in #2029
• Fix localtime() data race in the logger by @eakraly in #2030
• Log format: ISO-8601 timestamp by default, no thread id, space delimiter by @eakraly in #2031
• Keep the legacy random nonce at 16 chars by @eakraly in #2032
• Emit exactly one log line per record by @eakraly in #2033
• Enable stateless nonce by default by @eakraly in #2036

Full Changelog: 4.16.0...4.17.0