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Subsections

- `finger` variables
- `finger` event handlers

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The `finger` Analyzer

The `finger` analyzer processes traffic associated with the Finger service [RFC1288]. Bro instantiates a `finger` analyzer for any connection with service port `79/tcp` (if you `@load` the finger analyzer in your script, or define your own `finger_request` or `finger_reply` handlers, of course).

The analyzer uses a capture filter of ```port finger`'' (§ ).

In the past, attackers often used Finger requests to obtain information about a site's users, and sometimes to launch attacks of various forms (buffer overflows, in particular). In our experience, exploitation of the service has greatly diminished over the past years (no doubt in part to the service being increasingly turned off, or prohibited by firewalls). Now it is only rarely associated with an attack.

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`finger` variables

The standard script defines two redefinable variables:

  [``hot_names : set[string]``] A list of usernames that should be considered sensitive (log-worthy) if included in a Finger request.

  Default: `{ "root", "lp", "uucp", "nuucp", "demos", "operator", "sync", "guest", "visitor", }`.

  [``max_request_length : count``] The largest reasonable request size (used to flag possible buffer overflow attacks). Bro marks a connection as ``hot'' if its request exceeds this length, and truncates its logging of the request to this many bytes, followed by `"..."`.

  Default: `80`.

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`finger` event handlers

The standard script defines one event handler:

  [``finger_request (c: connection, request: string, full: bool)``] Invoked upon connection `c` having made the request `request`. The `full` flag is true if the request included the ``long format'' option (which the event engine will have removed from the request).

  The standard script flags long requests and truncates them as noted above, and then checks whether the request is for a name in `hot_names`. It then formats the request either by placing double quotation marks around it, or, if the request was empty--indicating a request for information on all users--the request is changed to the string `ALL` with no quotes around it.

  If the originator already made a request, then this additional request is placed in parentheses (though multiple requests violate the Finger protocol). If the request was for the `full` format, then the text ```(/W)`'' is appended to the request. Finally, the request is appended to the connection's `addl` field.

The event engine generates an additional event that the predefined `finger` script does not handle:

  [``finger_reply (c: connection, reply_line: string)``] Generated for each line of text sent in response to the originator's request.

Next: The frag Module Up: Analyzers and Events Previous: The dns Module Contents Index