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.\" ========================================================================
.\"
.IX Title "EXTCAP 4"
.TH EXTCAP 4 "2021-12-09" "3.4.10" "The Wireshark Network Analyzer"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
extcap \- The extcap interface
.SH "DESCRIPTION"
.IX Header "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.
.PP
Without extcap, a capture can always be achieved by directly writing to a capture file:
.PP
.Vb 2
\&    the\-esoteric\-binary \-\-the\-strange\-flag \-\-interface=stream1 \-\-file dumpfile.pcap &
\&    wireshark dumpfile.pcap
.Ve
.PP
but the extcap interface allows for such a connection to be easily established and
configured using the Wireshark \s-1GUI.\s0
.PP
The extcap subsystem is made of multiple extcap binaries that are automatically
called by the \s-1GUI\s0 in a row. In the following chapters we will refer to them as
\&\*(L"the extcaps\*(R".
.PP
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.
.PP
\&\s-1WINDOWS USER:\s0 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.
.PP
When Wireshark launches an extcap, it automatically adds its installation path
(c:\eProgram Files\eWireshark\e) to the \s-1DLL\s0 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.
.SH "GRAMMAR ELEMENTS"
.IX Header "GRAMMAR ELEMENTS"
Grammar elements:
.IP "arg (options)" 4
.IX Item "arg (options)"
argument for \s-1CLI\s0 calling
.IP "number" 4
.IX Item "number"
Reference # of argument for other values, display order
.IP "call" 4
.IX Item "call"
Literal argument to call (\-\-call=...)
.IP "display" 4
.IX Item "display"
Displayed name
.IP "default" 4
.IX Item "default"
Default value, in proper form for type
.IP "range" 4
.IX Item "range"
Range of valid values for \s-1UI\s0 checking (min,max) in proper form
.IP "type" 4
.IX Item "type"
Argument type for \s-1UI\s0 filtering for raw, or \s-1UI\s0 type for selector:
.Sp
.Vb 11
\&    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)
.Ve
.IP "value (options)" 4
.IX Item "value (options)"
.Vb 2
\&    Values for argument selection
\&    arg     Argument # this value applies to
.Ve
.SH "EXAMPLES"
.IX Header "EXAMPLES"
Example 1:
.PP
.Vb 8
\&    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}
.Ve
.PP
Example 2:
.PP
.Vb 3
\&    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}
.Ve
.PP
Example 3:
.PP
.Vb 3
\&    arg {number=0}{call=\-\-usbdevice}{USB Device}{type=selector}
\&    arg {number=1}{call=\-\-server}{display=IP address for log server}{type=string}{validation=(?:\ed{1,3}\e.){3}\ed{1,3}}
\&    flag {failure=Permission denied opening Ubertooth device}
.Ve
.PP
Example 4:
    arg {number=0}{call=\-\-username}{display=Username}{type=string}
    arg {number=1}{call=\-\-password}{display=Password}{type=password}
.PP
Example 5:
    arg {number=0}{call=\-\-start}{display=Start Time}{type=timestamp}
    arg {number=1}{call=\-\-end}{display=End Time}{type=timestamp}
.SH "Security awareness"
.IX Header "Security awareness"
.IP "\- Users running wireshark as root, we can't save you" 4
.IX Item "- Users running wireshark as root, we can't save you"
.PD 0
.IP "\- Dumpcap retains suid/setgid and group+x permissions to allow users in wireshark group only" 4
.IX Item "- Dumpcap retains suid/setgid and group+x permissions to allow users in wireshark group only"
.IP "\- Third-party capture programs run w/ whatever privs they're installed with" 4
.IX Item "- Third-party capture programs run w/ whatever privs they're installed with"
.IP "\- If an attacker can write to a system binary directory, we're game over anyhow" 4
.IX Item "- If an attacker can write to a system binary directory, we're game over anyhow"
.IP "\- Reference the folders tab in the wireshark\->about information, to see from which directory extcap is being run" 4
.IX Item "- Reference the folders tab in the wireshark->about information, to see from which directory extcap is being run"
.PD
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBwireshark\fR\|(1), \fBtshark\fR\|(1), \fBdumpcap\fR\|(1), \fBandroiddump\fR\|(1), \fBsshdump\fR\|(1), \fBrandpktdump\fR\|(1)
.SH "NOTES"
.IX Header "NOTES"
\&\fBExtcap\fR is feature of \fBWireshark\fR.  The latest version
of \fBWireshark\fR can be found at <https://www.wireshark.org>.
.PP
\&\s-1HTML\s0 versions of the Wireshark project man pages are available at:
<https://www.wireshark.org/docs/man\-pages>.