extcap(4) The Wireshark Network Analyzer extcap(4)
NAME
extcap - The extcap interface
DESCRIPTION
The extcap 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 directory. Please
note, that scripts need to be executable without prefacing a script
interpreter before the call.
WINDOWS USER: 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 (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 (executable, 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)
float
selector (display selector table, all values as strings)
boolean (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)
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:
arg {number=0}{call=--start}{display=Start Time}{type=timestamp}
arg {number=1}{call=--end}{display=End Time}{type=timestamp}
Security awareness
- Users running wireshark as root, we can't save you
- Dumpcap retains suid/setgid and group+x permissions to allow users in
wireshark group only
- Third-party capture programs run w/ whatever privs they're installed
with
- If an attacker can write to a system binary directory, we're game
over anyhow
- Reference the folders tab in the wireshark->about information, to see
from which directory extcap is being run
SEE ALSO
wireshark(1), tshark(1), dumpcap(1), androiddump(1), sshdump(1),
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>.
3.4.7 2021-07-14 extcap(4)
wireshark 3.4.7 - Generated Wed Jul 21 07:44:36 CDT 2021