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include::../attributes.adoc[]
= extcap(4)
:doctype: manpage
:stylesheet: ws.css
:linkcss:
:copycss: {css_dir}/{stylesheet}
== NAME
extcap - The external capture interface
== DESCRIPTION
The extcap (external capture) interface is a versatile plugin interface that allows external binaries
to act as capture interfaces directly in Wireshark. It is used in scenarios, where
the source of the capture is not a traditional capture model
(live capture from an interface, from a pipe, from a file, etc). The typical
example is connecting esoteric hardware of some kind to the main Wireshark application.
Without extcap, a capture can always be achieved by directly writing to a capture file:
the-esoteric-binary --the-strange-flag --interface=stream1 --file dumpfile.pcap &
wireshark dumpfile.pcap
but the extcap interface allows for such a connection to be easily established and
configured using the Wireshark GUI.
The extcap subsystem is made of multiple extcap binaries that are automatically
called by the GUI in a row. In the following chapters we will refer to them as
"the extcaps".
Extcaps may be any binary or script within the _extcap/wireshark_ or _extcap/stratoshark_ directories.
Please note that scripts need to be executable without prefacing a script interpreter before the call.
WINDOWS USERS: Because of restrictions directly calling the script may not always work.
In such a case, a batch file may be provided, which then in turn executes the script. Please
refer to doc/extcap_example.py for more information.
When Wireshark launches an extcap, it automatically adds its installation path (normally _C:\Program Files\Wireshark\_) to the DLL search path so that the extcap library dependencies can be found (it is not designed to be launched by hand).
This is done on purpose. There should only be extcap programs (executables, Python scripts, ...) in the extcap folder to reduce the startup time and not have Wireshark trying to execute other file types.
== GRAMMAR ELEMENTS
Grammar elements:
arg (options)::
argument for CLI calling
number::
Reference # of argument for other values, display order
call::
Literal argument to call (--call=...)
display::
Displayed name
default::
Default value, in proper form for type
range::
Range of valid values for UI checking (min,max) in proper form
type::
+
--
Argument type for UI filtering for raw, or UI type for selector:
integer
unsigned
long (may include scientific / special notation)
double
string (display a textbox)
selector (display selector table, all values as strings)
editselector (selector table which can be overridden, all values as strings)
boolean (display checkbox)
booleanflag (display checkbox)
radio (display group of radio buttons with provided values, all values as strings)
fileselect (display a dialog to select a file from the filesystem, value as string)
multicheck (display a textbox for selecting multiple options, values as strings)
table (display a table that is populated by the user, selections can be configured, values as commandlines arguments)
password (display a textbox with masked text)
timestamp (display a calendar)
--
value (options)::
+
--
Values for argument selection
arg Argument # this value applies to
--
== EXAMPLES
Example 1:
arg {number=0}{call=--channel}{display=Wi-Fi Channel}{type=integer}{required=true}
arg {number=1}{call=--chanflags}{display=Channel Flags}{type=radio}
arg {number=2}{call=--interface}{display=Interface}{type=selector}
value {arg=0}{range=1,11}
value {arg=1}{value=ht40p}{display=HT40+}
value {arg=1}{value=ht40m}{display=HT40-}
value {arg=1}{value=ht20}{display=HT20}
value {arg=2}{value=wlan0}{display=wlan0}
Example 2:
arg {number=0}{call=--usbdevice}{USB Device}{type=selector}
value {arg=0}{call=/dev/sysfs/usb/foo/123}{display=Ubertooth One sn 1234}
value {arg=0}{call=/dev/sysfs/usb/foo/456}{display=Ubertooth One sn 8901}
Example 3:
arg {number=0}{call=--usbdevice}{USB Device}{type=selector}
arg {number=1}{call=--server}{display=IP address for log server}{type=string}{validation=(?:\d{1,3}\.){3}\d{1,3}}
flag {failure=Permission denied opening Ubertooth device}
Example 4:
arg {number=0}{call=--username}{display=Username}{type=string}
arg {number=1}{call=--password}{display=Password}{type=password}
Example 5: timestamp
arg {number=0}{call=--start}{display=Start Time}{type=timestamp}
arg {number=1}{call=--end}{display=End Time}{type=timestamp}
Example 6: multicheck
arg {number=0}{call=--device}{display=Device}{type=multicheck}
value {arg=0}{value=USBDEV}{display=USB devices}{enabled=false}
value {arg=0}{value=/dev/sysfs/usb/foo/123}{display=Ubertooth One sn 1234}{parent=USBDEV}
value {arg=0}{value=/dev/sysfs/usb/foo/456}{display=Ubertooth One sn 8901}{parent=USBDEV}
value {arg=0}{value=PCIDEV}{display=PCI devices}{enabled=false}
value {arg=0}{value=/sys/devices/pci123}{display=Device 1}{parent=PCIDEV}
value {arg=0}{value=/sys/devices/pci456}{display=Device 2}{parent=PCIDEV}
== Table field
The "table" field is a bit different, in that its values can have additional configuration options.
The values can either be entered manually by the user, or a list of available values can be provided using the same
API as "multicheck".
Unlike most APIs, the value is provided using a commandline-like API, separated by spaces instead of comas. For instance,
a configured "myparam" attribute where the user selected three values (1, 2 and 3) would receive:
--myparam "1 2 3"
If a "prefix" is configured to be "--p", it would receive the following:
--myparam "--p 1 --p 2 --p 3"
The values selected in a table field may have specific configuration options, if "configurable=true" for the "multicheck" field.
In this case, the extcap will be called again when the user presses the configuration wheel that matches a value in the table,
with the additional "--extcap-config-option-name <option_name> --extcap-config-option-value <option_value>" with no prefix.
An extcap program should respond with an additional set of arguments, which will be opened in a popup. Once those are configured,
the extcap might get the following, assuming for instance that an additional "param1" is requested when value is 1, and "param2"
when value is 2.
--myparam "--p 1 --param1 1 --p 2 --param2 true --p 3"
== Security Considerations
- If you're running Wireshark as root, we can't save you.
- Dumpcap retains suid/setgid and group execute permissions for users in the “wireshark” group only.
- Third-party capture programs run with whatever privileges they're installed with.
- If an attacker can write to a system binary directory, it's game over.
- You can find your local extcap directory in menu:About[Folders].
== SEE ALSO
xref:wireshark.html[wireshark](1), xref:tshark.html[tshark](1), xref:dumpcap.html[dumpcap](1), xref:androiddump.html[androiddump](1), xref:sshdig.html[sshdig](1), xref:sshdump.html[sshdump](1), xref:randpktdump.html[randpktdump](1)
== NOTES
*Extcap* is feature of *Wireshark*.
The latest version of *Wireshark* can be found at https://www.wireshark.org.
HTML versions of the Wireshark project man pages are available at
https://www.wireshark.org/docs/man-pages.
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