gridftp.zeek

GridFTP

A detection script for GridFTP data and control channels.

GridFTP control channels are identified by FTP control channels that successfully negotiate the GSSAPI method of an AUTH request and for which the exchange involved an encoded TLS/SSL handshake, indicating the GSI mechanism for GSSAPI was used. This analysis is all supported internally, this script simply adds the “gridftp” label to the service field of the control channel’s connection record.

GridFTP data channels are identified by a heuristic that relies on the fact that default settings for GridFTP clients typically mutually authenticate the data channel with TLS/SSL and negotiate a NULL bulk cipher (no encryption). Connections with those attributes are marked as GridFTP if the data transfer within the first two minutes is big enough to indicate a GripFTP data channel that would be undesirable to analyze further (e.g. stop TCP reassembly). A side effect is that true connection sizes are not logged, but at the benefit of saving CPU cycles that would otherwise go to analyzing the large (and likely benign) connections.

Namespace: GridFTP
Imports: base/frameworks/notice, base/protocols/conn, base/protocols/ftp/info.zeek, base/protocols/ftp/main.zeek, base/protocols/ssl

Summary

Runtime Options

`GridFTP::max_time`: `interval` `&redef`	Time during which we check whether a connection’s size exceeds the `GridFTP::size_threshold`.
`GridFTP::size_threshold`: `count` `&redef`	Number of bytes transferred before guessing a connection is a GridFTP data channel.
`GridFTP::skip_data`: `bool` `&redef`	Whether to skip further processing of the GridFTP data channel once detected, which may help performance.

Redefinitions

FTP::Info: record

New Fields

FTP::Info

last_auth_requested: string &optional

Events

GridFTP::data_channel_detected: event

Raised when a GridFTP data channel is detected.

Functions

GridFTP::data_channel_initial_criteria: function &redef

The initial criteria used to determine whether to start polling the connection for the GridFTP::size_threshold to have been exceeded.

Detailed Interface

Runtime Options

GridFTP::max_time 

Type: interval
Attributes: &redef
Default: 2.0 mins

Time during which we check whether a connection’s size exceeds the GridFTP::size_threshold.

GridFTP::size_threshold 

Type: count
Attributes: &redef
Default: 1073741824

Number of bytes transferred before guessing a connection is a GridFTP data channel.

GridFTP::skip_data 

Type: bool
Attributes: &redef
Default: T

Whether to skip further processing of the GridFTP data channel once detected, which may help performance.

Events

GridFTP::data_channel_detected 

Type: event (c: connection)

Raised when a GridFTP data channel is detected.

Parameters: c – The connection pertaining to the GridFTP data channel.

Functions

GridFTP::data_channel_initial_criteria 

Type: function (c: connection) : bool
Attributes: &redef

The initial criteria used to determine whether to start polling the connection for the GridFTP::size_threshold to have been exceeded. This is called in a ssl_established event handler and by default looks for both a client and server certificate and for a NULL bulk cipher. One way in which this function could be redefined is to make it also consider client/server certificate issuer subjects.

Parameters: c – The connection which may possibly be a GridFTP data channel.
Returns: true if the connection should be further polled for an exceeded GridFTP::size_threshold, else false.