oracular (7) syncthing-security.7.gz

NAME

       syncthing-security - Security Principles

       Security  is  one of the primary project goals. This means that it should not be possible for an attacker
       to join a cluster uninvited,  and  it  should  not  be  possible  to  extract  private  information  from
       intercepted traffic. Currently this is implemented as follows.

       All  device  to  device traffic is protected by TLS. To prevent uninvited devices from joining a cluster,
       the certificate fingerprint of each device is  compared  to  a  preset  list  of  acceptable  devices  at
       connection  establishment.  The  fingerprint  is  computed  as  the  SHA-256  hash of the certificate and
       displayed in a human-friendly encoding, called Device ID.

       Incoming requests for file data are verified to the extent that the requested file name must exist in the
       local index and the global model.

       For  information  about  ensuring  you  are running the code you think you are and for reporting security
       vulnerabilities, please see the official security page <https://syncthing.net/security>.

INFORMATION LEAKAGE

   Global Discovery
       When global discovery is enabled, Syncthing  sends  an  announcement  every  30  minutes  to  the  global
       discovery  servers  so  that  they  can  keep  a  mapping  between  your  device  ID and external IP. The
       announcement contain the device ID and listening port(s). Also, when connecting  to  other  devices  that
       have  not  been seen on the local network, a query is sent to the global discovery servers containing the
       device ID of the requested device. The connection to the discovery server is encrypted using TLS and  the
       discovery  server  certificate  is  verified,  so  the contents of the query should be considered private
       between the device and the discovery server.  The  discovery  servers  are  currently  hosted  by  @calmh
       <https://github.com/calmh>. Global discovery defaults to on.

       When  turned  off,  devices with dynamic addresses not on the local network cannot be found and connected
       to.

       An eavesdropper on the Internet can deduce which machines are running  Syncthing  with  global  discovery
       enabled, and what their device IDs are.

       The operator of the discovery server can map arbitrary device addresses to IP addresses, and deduce which
       devices are connected to each other.

       If a different global discovery server is configured, no data is sent to  the  default  global  discovery
       servers.

   Local Discovery
       When  local  discovery  is  enabled, Syncthing sends broadcast (IPv4) and multicast (IPv6) packets to the
       local network every 30 seconds. The packets contain the device ID and  listening  port.  Local  discovery
       defaults to on.

       An eavesdropper on the local network can deduce which machines are running Syncthing with local discovery
       enabled, and what their device IDs are.

       When turned off, devices with dynamic addresses on the local network cannot be found and connected to.

   Upgrade Checks
       When automatic upgrades are enabled, Syncthing checks for a new version at startup and  then  once  every
       twelve  hours.  This is by an HTTPS request to the download site for releases, currently hosted by @calmh
       <https://github.com/calmh>.  Automatic upgrades  default  to  on  (unless  Syncthing  was  compiled  with
       upgrades disabled).

       Even  when  automatic  upgrades are disabled in the configuration, an upgrade check as above is done when
       the GUI is loaded, in order to show the “Upgrade to …” button when necessary. This can be  disabled  only
       by compiling Syncthing with upgrades disabled.

       The actual download, should an upgrade be available, is done from GitHub, thus exposing the user to them.

       The  upgrade  check  (or download) requests do not contain any identifiable information about the user or
       device.

   Usage Reporting
       When usage reporting is enabled, Syncthing reports usage data at startup and then  every  24  hours.  The
       report   is  sent  as  an  HTTPS  POST  to  the  usage  reporting  server,  currently  hosted  by  @calmh
       <https://github.com/calmh>. The contents of the usage report can be seen behind  the  “Preview”  link  in
       settings.  Usage reporting defaults to off but the GUI will ask once about enabling it, shortly after the
       first install.

       The reported data is protected from eavesdroppers, but the  connection  to  the  usage  reporting  server
       itself may expose the client as running Syncthing.

   Sync Connections (BEP)
       Sync  connections  are  attempted to all configured devices, when the address is possible to resolve. The
       sync connection is based on TLS 1.2 or TLS 1.3. The TLS certificates can be obtained by an  eavesdropper,
       although  it  is  more difficult to do so in TLS 1.3. This means that the contents of the certificate are
       visible, which includes certificate Common Name (by default syncthing).

       An eavesdropper can deduce that this is a Syncthing connection and under certain circumstances  calculate
       the device IDs involved based on the hashes of the sent certificates.

       Likewise,  if  the sync port (default 22000) is accessible from the internet, a port scanner may discover
       it, attempt a TLS negotiation and thus obtain the device certificate. This provides the same  information
       as in the eavesdropper case.

   Relay Connections
       When  relaying is enabled, Syncthing will look up the pool of public relays and establish a connection to
       one of them (the best, based on an  internal  heuristic).  The  selected  relay  server  will  learn  the
       connecting  device’s  device  ID.  Relay  servers  can  be run by anyone in the general public.  Relaying
       defaults to on. Syncthing can be configured to disable relaying, or only use specific relays.

       If a relay connections is required between two devices, the relay will learn the other device’s device ID
       as well.

       Any  data  exchanged  between  the two devices is encrypted as usual and not subject to inspection by the
       relay.

   Web GUI
       If the web GUI is accessible, it exposes the device as running Syncthing. The web GUI defaults  to  being
       reachable from the local host only.

IN SHORT

       Parties  doing  surveillance on your network (whether that be corporate IT, the NSA or someone else) will
       be  able  to  see  that  you  use  Syncthing,  and   your   device   IDs   are   OK   to   share   anyway
       <https://docs.syncthing.net/users/faq.html#should-i-keep-my-device-ids-secret>,     but     the    actual
       transmitted data is protected as well as we can. Knowing your device ID can expose your IP address, using
       global discovery.

PROTECTING YOUR SYNCTHING KEYS AND IDENTITY

       Anyone  who can access the Syncthing TLS keys and config file on your device can impersonate your device,
       connect to your peers, and then have access to your synced files. Here are  some  general  principles  to
       protect your files:

       1. If a device of yours is lost, make sure to revoke its access from your other devices.

       2. If  you’re  syncing  confidential  data  on  an  encrypted disk to guard against device theft, put the
          Syncthing config folder on the same encrypted disk to avoid leaking keys and metadata. Or,  use  whole
          disk encryption.

AUTHOR

       The Syncthing Authors

COPYRIGHT

       2014-2019, The Syncthing Authors