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Fedora Update Notification
FEDORA-2025-29fc4fefd5
2025-02-05 02:09:51.857790+00:00
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Name        : fastd
Product     : Fedora 40
Version     : 23
Release     : 1.fc40
URL         : https://github.com/neocturne/fastd
Summary     : Fast and secure tunneling daemon
Description :
fastd is a secure tunneling daemon with some unique features:

 - Very small binary (about 100KB on OpenWRT in the default configuration,
   including all dependencies besides libc)
 - Exchangable crypto methods
 - Transport over UDP for simple usage behind NAT
 - Can run in 1:1 and 1:n scenarios
 - There are no server and client roles defined by the protocol, this is just
   defined by the usage.
 - Only one instance of the daemon is needed on each host to create a full mesh
   If no full mesh is established, a routing protocol is necessary to enable
   hosts that are not connected directly to reach each other

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Update Information:

This release contains a number of small improvements and bugfixes, including
mitigations for the LOW severity vulnerability CVE-2025-24356.
Bugfixes
Add mitigations for fast-reconnect amplification attacks
When receiving a data packet from an unknown IP address/port combination, fastd
will assume that one of its connected peers has moved to a new address (for
example due to internet lines with dynamic IP, or roaming between WWAN and a
local internet connection) and initiate a reconnect by sending a handshake
packet. This “fast reconnect” avoids having to wait for a session timeout (up to
~90s) until a new connection is established.
Even a 1-byte UDP packet just containing the fastd packet type header can
trigger a much larger handshake packet (~150 bytes of UDP payload). With fastd
v22, this number is doubled, because two handshakes are sent (one in a
pre-v22-compatible format and one in a new L2TP-style format). Including IPv4
and UDP headers, the resulting amplification factor is roughly 12-13.
By sending data packets with a spoofed source address to fastd instances
reachable on the internet, this amplification of UDP traffic might be used to
facilitate a Distributed Denial of Service attack.
fastd has always implemented rate limiting for handshakes to unknown IP
addresses and ports to 1 handshake per 15s to avoid this kind of attack, however
the rate is limited per-port and not per-address, thus still allowing handshakes
to be sent to all 65535 UDP ports of the same IP address unlimited.
The issue has been mitigated in fastd v23 by a number of changes:
Rate-limiting has been changed changed to be applied per-address instead of per-
port
Only one handshake instead of two handshakes is sent for fast-reconnect (by
determining from the format of the data packet whether a pre-v22 or L2TP-style
handshake should be used)
Require at least a full method header instead of just a single byte for a data
packet to be considered valid. This does not have an effect on instances that
enable the null method (regardless of null being actually in use), as a single-
byte UDP packet is a valid null keepalive, but for all other methods the
amplification factor is slightly reduced.
Only fastd instances that allow connections from arbitrary IP addresses are
vulnerable. Instances in a “client” role that configure their peers using the
remote config option (which includes the common deployment as part of the Gluon
wireless mesh firmware) will not respond to unexpected data packets with a
handshake and are therefore unaffected.
CVE-2025-24356 has been assigned to this issue. The severity of this
vulnerability is considered LOW.
A GitHub security advisory can be found under GHSA-pggg-vpfv-4rcv.
Fix config loading to fail on offload l2tp no; when L2TP offloading is
unsupported by the fastd build or the kernel
Fix assembly Salsa20(/12) implementations accidentally generating the Linux-
specific .note.GNU-stack ELF section on non-Linux systems
This is unlikely to have caused any issues, as other systems should just ignore
the unknown section.
Status socket: - Fix interface name information with L2TP offloading - Add per-
peer MTU information
Documentation: - Fix incorrect “persist interface” examples - Improve
explanation of float option
Build: - Fix build on macOS (again) - Fix build with Meson 0.49 (the minimum
version marked as supported by fastd)
Other changes
Add support for Indirect Branch Tracking and Shadow Stacks on x86
The assembly Salsa20(/12) implementations have been marked compatible with IBT
and SHSTK, which are part of Intel CET (Control-flow Enforcement Technology) and
can be enabled using the -fcf-protection GCC option.
The file COPYRIGHT has been renamed to LICENSE
The vendored version of libmnl that is used with libmnl_builtin=true has been
updated to 1.0.5
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ChangeLog:

* Sun Jan 26 2025 Felix Kaechele  - 23-1
- update to 23
* Thu Jan 16 2025 Fedora Release Engineering  - 22-17
- Rebuilt for https://fedoraproject.org/wiki/Fedora_42_Mass_Rebuild
* Wed Jul 17 2024 Fedora Release Engineering  - 22-16
- Rebuilt for https://fedoraproject.org/wiki/Fedora_41_Mass_Rebuild
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References:

  [ 1 ] Bug #2342133 - fastd-23 is available
        https://bugzilla.redhat.com/show_bug.cgi?id=2342133
  [ 2 ] Bug #2342337 - CVE-2025-24356 fastd: UDP traffic amplification via fastd's fast reconnect feature [fedora-40]
        https://bugzilla.redhat.com/show_bug.cgi?id=2342337
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This update can be installed with the "dnf" update program. Use
su -c 'dnf upgrade --advisory FEDORA-2025-29fc4fefd5' at the command
line. For more information, refer to the dnf documentation available at
http://dnf.readthedocs.io/en/latest/command_ref.html#upgrade-command-label

All packages are signed with the Fedora Project GPG key. More details on the
GPG keys used by the Fedora Project can be found at
https://fedoraproject.org/keys
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