174 lines
7.7 KiB
Groff
174 lines
7.7 KiB
Groff
.\" Man page generated from reStructuredText.
|
||
.
|
||
.TH "SYNCTHING-SECURITY" "7" "Jan 14, 2019" "v1" "Syncthing"
|
||
.SH NAME
|
||
syncthing-security \- Security Principles
|
||
.
|
||
.nr rst2man-indent-level 0
|
||
.
|
||
.de1 rstReportMargin
|
||
\\$1 \\n[an-margin]
|
||
level \\n[rst2man-indent-level]
|
||
level margin: \\n[rst2man-indent\\n[rst2man-indent-level]]
|
||
-
|
||
\\n[rst2man-indent0]
|
||
\\n[rst2man-indent1]
|
||
\\n[rst2man-indent2]
|
||
..
|
||
.de1 INDENT
|
||
.\" .rstReportMargin pre:
|
||
. RS \\$1
|
||
. nr rst2man-indent\\n[rst2man-indent-level] \\n[an-margin]
|
||
. nr rst2man-indent-level +1
|
||
.\" .rstReportMargin post:
|
||
..
|
||
.de UNINDENT
|
||
. RE
|
||
.\" indent \\n[an-margin]
|
||
.\" old: \\n[rst2man-indent\\n[rst2man-indent-level]]
|
||
.nr rst2man-indent-level -1
|
||
.\" new: \\n[rst2man-indent\\n[rst2man-indent-level]]
|
||
.in \\n[rst2man-indent\\n[rst2man-indent-level]]u
|
||
..
|
||
.sp
|
||
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.
|
||
.sp
|
||
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 BASE32 encoding to form a reasonably compact and convenient string.
|
||
.sp
|
||
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.
|
||
.sp
|
||
For information about ensuring you are running the code you think you are and
|
||
for reporting security vulnerabilities, please see the official \fI\%security page\fP <\fBhttps://syncthing.net/security.html\fP>\&.
|
||
.SH INFORMATION LEAKAGE
|
||
.SS Global Discovery
|
||
.sp
|
||
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 \fI\%@calmh\fP <\fBhttps://github.com/calmh\fP>\&. Global discovery defaults to \fBon\fP\&.
|
||
.sp
|
||
When turned off, devices with dynamic addresses not on the local network cannot
|
||
be found and connected to.
|
||
.sp
|
||
An eavesdropper on the Internet can deduce which machines are running
|
||
Syncthing with global discovery enabled, and what their device IDs are.
|
||
.sp
|
||
The operator of the discovery server can map arbitrary device addresses to
|
||
IP addresses, and deduce which devices are connected to each other.
|
||
.sp
|
||
If a different global discovery server is configured, no data is sent to the
|
||
default global discovery servers.
|
||
.SS Local Discovery
|
||
.sp
|
||
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 \fBon\fP\&.
|
||
.sp
|
||
An eavesdropper on the local network can deduce which machines are running
|
||
Syncthing with local discovery enabled, and what their device IDs are.
|
||
.sp
|
||
When turned off, devices with dynamic addresses on the local network cannot be
|
||
found and connected to.
|
||
.SS Upgrade Checks
|
||
.sp
|
||
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 \fI\%@calmh\fP <\fBhttps://github.com/calmh\fP>\&.
|
||
Automatic upgrades default to \fBon\fP (unless Syncthing was compiled with
|
||
upgrades disabled).
|
||
.sp
|
||
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.
|
||
.sp
|
||
The actual download, should an upgrade be available, is done from
|
||
\fBGitHub\fP, thus exposing the user to them.
|
||
.sp
|
||
The upgrade check (or download) requests \fIdo not\fP contain any identifiable
|
||
information about the user or device.
|
||
.SS Usage Reporting
|
||
.sp
|
||
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 \fI\%@calmh\fP <\fBhttps://github.com/calmh\fP>\&. The contents of the usage report can
|
||
be seen behind the “Preview” link in settings. Usage reporting defaults to
|
||
\fBoff\fP but the GUI will ask once about enabling it, shortly after the first
|
||
install.
|
||
.sp
|
||
The reported data is protected from eavesdroppers, but the connection to the
|
||
usage reporting server itself may expose the client as running Syncthing.
|
||
.SS Sync Connections (BEP)
|
||
.sp
|
||
Sync connections are attempted to all configured devices, when the address is
|
||
possible to resolve. The sync connection is based on TLS 1.2. The TLS
|
||
certificates are sent in clear text (as in HTTPS etc), meaning that the
|
||
certificate Common Name (by default \fBsyncthing\fP) is visible.
|
||
.sp
|
||
An eavesdropper can deduce that this is a Syncthing connection and calculate the
|
||
device IDs involved based on the hashes of the sent certificates.
|
||
.sp
|
||
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.
|
||
.SS Relay Connections
|
||
.sp
|
||
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 \fBanyone in the general public\fP\&.
|
||
Relaying defaults to \fBon\fP\&. Syncthing can be configured to disable
|
||
relaying, or only use specific relays.
|
||
.sp
|
||
If a relay connections is required between two devices, the relay will learn
|
||
the other device’s device ID as well.
|
||
.sp
|
||
Any data exchanged between the two devices is encrypted as usual and not
|
||
subject to inspection by the relay.
|
||
.SS Web GUI
|
||
.sp
|
||
If the web GUI is accessible, it exposes the device as running Syncthing. The
|
||
web GUI defaults to being reachable from the \fBlocal host only\fP\&.
|
||
.SH IN SHORT
|
||
.sp
|
||
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 \fI\%are OK to share anyway\fP <\fBhttps://docs.syncthing.net/users/faq.html#should-i-keep-my-device-ids-secret\fP>,
|
||
but the actual transmitted data is protected as well as we can. Knowing your
|
||
device ID can expose your IP address, using global discovery.
|
||
.SH PROTECTING YOUR SYNCTHING KEYS AND IDENTITY
|
||
.sp
|
||
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:
|
||
.INDENT 0.0
|
||
.IP 1. 3
|
||
If a device of yours is lost, make sure to revoke its access from your other
|
||
devices.
|
||
.IP 2. 3
|
||
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.
|
||
.UNINDENT
|
||
.SH AUTHOR
|
||
The Syncthing Authors
|
||
.SH COPYRIGHT
|
||
2014-2018, The Syncthing Authors
|
||
.\" Generated by docutils manpage writer.
|
||
.
|