# extcap

## 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 _About › Folders_.
    


## 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. This page is part of the
           _wireshark_ (Interactively dump and analyze network traffic)
           project. Information about the project can be found at 
           ⟨https://www.wireshark.org/⟩. If you have a bug report for this
           manual page, see
           ⟨https://gitlab.com/wireshark/wireshark/-/issues⟩. This page was
           obtained from the project's upstream Git repository
           ⟨https://gitlab.com/wireshark/wireshark.git⟩ on 2025-08-11. (At
           that time, the date of the most recent commit that was found in
           the repository was 2025-08-11.) If you discover any rendering
           problems in this HTML version of the page, or you believe there is
           a better or more up-to-date source for the page, or you have
           corrections or improvements to the information in this COLOPHON
           (which is _not_ part of the original manual page), send a mail to
           man-pages@man7.org
    
                                    2025-08-09                      _EXTCAP_(4)
    


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