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.\" ========================================================================
.\"
.IX Title "EXTCAP 4"
.TH EXTCAP 4 "2021-01-30" "2.6.20" "The Wireshark Network Analyzer"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.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 app.
.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. To go deeper
into the extcap utility development, please refer to \s-1README\s0.extcap.
.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.
.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>.