Windows Event Log (EVT): GraphViz block diagram (.dot) source

EVT files are Windows Event Log files written by older Windows operating systems (2000, XP, 2003). They are used as binary log files by several major Windows subsystems and applications. Typically, several of them can be found in %WINDIR%\system32\config directory:

  • Application = AppEvent.evt
  • System = SysEvent.evt
  • Security = SecEvent.evt

Alternatively, one can export any system event log as distinct .evt file using relevant option in Event Viewer application.

A Windows application can submit an entry into these logs using ReportEvent function of Windows API.

Internally, EVT files consist of a fixed-size header and event records. There are several usage scenarios (non-wrapping vs wrapping log files) which result in slightly different organization of records.

File extension

evt

KS implementation details

License: CC0-1.0

This page hosts a formal specification of Windows Event Log (EVT) using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.

GraphViz block diagram source

windows_evt_log.dot

digraph {
	rankdir=LR;
	node [shape=plaintext];
	subgraph cluster__windows_evt_log {
		label="WindowsEvtLog";
		graph[style=dotted];

		windows_evt_log__seq [label=<<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
			<TR><TD BGCOLOR="#E0FFE0">pos</TD><TD BGCOLOR="#E0FFE0">size</TD><TD BGCOLOR="#E0FFE0">type</TD><TD BGCOLOR="#E0FFE0">id</TD></TR>
			<TR><TD PORT="header_pos">0</TD><TD PORT="header_size">48</TD><TD>Header</TD><TD PORT="header_type">header</TD></TR>
			<TR><TD PORT="records_pos">48</TD><TD PORT="records_size">...</TD><TD>Record</TD><TD PORT="records_type">records</TD></TR>
			<TR><TD COLSPAN="4" PORT="records__repeat">repeat to end of stream</TD></TR>
		</TABLE>>];
		subgraph cluster__header {
			label="WindowsEvtLog::Header";
			graph[style=dotted];

			header__seq [label=<<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
				<TR><TD BGCOLOR="#E0FFE0">pos</TD><TD BGCOLOR="#E0FFE0">size</TD><TD BGCOLOR="#E0FFE0">type</TD><TD BGCOLOR="#E0FFE0">id</TD></TR>
				<TR><TD PORT="len_header_pos">0</TD><TD PORT="len_header_size">4</TD><TD>u4le</TD><TD PORT="len_header_type">len_header</TD></TR>
				<TR><TD PORT="magic_pos">4</TD><TD PORT="magic_size">4</TD><TD>4C 66 4C 65</TD><TD PORT="magic_type">magic</TD></TR>
				<TR><TD PORT="version_major_pos">8</TD><TD PORT="version_major_size">4</TD><TD>u4le</TD><TD PORT="version_major_type">version_major</TD></TR>
				<TR><TD PORT="version_minor_pos">12</TD><TD PORT="version_minor_size">4</TD><TD>u4le</TD><TD PORT="version_minor_type">version_minor</TD></TR>
				<TR><TD PORT="ofs_start_pos">16</TD><TD PORT="ofs_start_size">4</TD><TD>u4le</TD><TD PORT="ofs_start_type">ofs_start</TD></TR>
				<TR><TD PORT="ofs_end_pos">20</TD><TD PORT="ofs_end_size">4</TD><TD>u4le</TD><TD PORT="ofs_end_type">ofs_end</TD></TR>
				<TR><TD PORT="cur_rec_idx_pos">24</TD><TD PORT="cur_rec_idx_size">4</TD><TD>u4le</TD><TD PORT="cur_rec_idx_type">cur_rec_idx</TD></TR>
				<TR><TD PORT="oldest_rec_idx_pos">28</TD><TD PORT="oldest_rec_idx_size">4</TD><TD>u4le</TD><TD PORT="oldest_rec_idx_type">oldest_rec_idx</TD></TR>
				<TR><TD PORT="len_file_max_pos">32</TD><TD PORT="len_file_max_size">4</TD><TD>u4le</TD><TD PORT="len_file_max_type">len_file_max</TD></TR>
				<TR><TD PORT="flags_pos">36</TD><TD PORT="flags_size">4</TD><TD>Flags</TD><TD PORT="flags_type">flags</TD></TR>
				<TR><TD PORT="retention_pos">40</TD><TD PORT="retention_size">4</TD><TD>u4le</TD><TD PORT="retention_type">retention</TD></TR>
				<TR><TD PORT="len_header_2_pos">44</TD><TD PORT="len_header_2_size">4</TD><TD>u4le</TD><TD PORT="len_header_2_type">len_header_2</TD></TR>
			</TABLE>>];
			subgraph cluster__flags {
				label="WindowsEvtLog::Header::Flags";
				graph[style=dotted];

				flags__seq [label=<<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
					<TR><TD BGCOLOR="#E0FFE0">pos</TD><TD BGCOLOR="#E0FFE0">size</TD><TD BGCOLOR="#E0FFE0">type</TD><TD BGCOLOR="#E0FFE0">id</TD></TR>
					<TR><TD PORT="reserved_pos">0</TD><TD PORT="reserved_size">28b</TD><TD>b28</TD><TD PORT="reserved_type">reserved</TD></TR>
					<TR><TD PORT="archive_pos">3:4</TD><TD PORT="archive_size">1b</TD><TD>BitsType1</TD><TD PORT="archive_type">archive</TD></TR>
					<TR><TD PORT="log_full_pos">3:5</TD><TD PORT="log_full_size">1b</TD><TD>BitsType1</TD><TD PORT="log_full_type">log_full</TD></TR>
					<TR><TD PORT="wrap_pos">3:6</TD><TD PORT="wrap_size">1b</TD><TD>BitsType1</TD><TD PORT="wrap_type">wrap</TD></TR>
					<TR><TD PORT="dirty_pos">3:7</TD><TD PORT="dirty_size">1b</TD><TD>BitsType1</TD><TD PORT="dirty_type">dirty</TD></TR>
				</TABLE>>];
			}
		}
		subgraph cluster__record {
			label="WindowsEvtLog::Record";
			graph[style=dotted];

			record__seq [label=<<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
				<TR><TD BGCOLOR="#E0FFE0">pos</TD><TD BGCOLOR="#E0FFE0">size</TD><TD BGCOLOR="#E0FFE0">type</TD><TD BGCOLOR="#E0FFE0">id</TD></TR>
				<TR><TD PORT="len_record_pos">0</TD><TD PORT="len_record_size">4</TD><TD>u4le</TD><TD PORT="len_record_type">len_record</TD></TR>
				<TR><TD PORT="type_pos">4</TD><TD PORT="type_size">4</TD><TD>u4le</TD><TD PORT="type_type">type</TD></TR>
				<TR><TD PORT="body_pos">8</TD><TD PORT="body_size">...</TD><TD>switch (type)</TD><TD PORT="body_type">body</TD></TR>
				<TR><TD PORT="len_record2_pos">...</TD><TD PORT="len_record2_size">4</TD><TD>u4le</TD><TD PORT="len_record2_type">len_record2</TD></TR>
			</TABLE>>];
record__seq_body_switch [label=<<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
	<TR><TD BGCOLOR="#F0F2E4">case</TD><TD BGCOLOR="#F0F2E4">type</TD></TR>
	<TR><TD>1699505740</TD><TD PORT="case0">RecordBody</TD></TR>
	<TR><TD>286331153</TD><TD PORT="case1">CursorRecordBody</TD></TR>
</TABLE>>];
		}
		subgraph cluster__record_body {
			label="WindowsEvtLog::RecordBody";
			graph[style=dotted];

			record_body__seq [label=<<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
				<TR><TD BGCOLOR="#E0FFE0">pos</TD><TD BGCOLOR="#E0FFE0">size</TD><TD BGCOLOR="#E0FFE0">type</TD><TD BGCOLOR="#E0FFE0">id</TD></TR>
				<TR><TD PORT="idx_pos">0</TD><TD PORT="idx_size">4</TD><TD>u4le</TD><TD PORT="idx_type">idx</TD></TR>
				<TR><TD PORT="time_generated_pos">4</TD><TD PORT="time_generated_size">4</TD><TD>u4le</TD><TD PORT="time_generated_type">time_generated</TD></TR>
				<TR><TD PORT="time_written_pos">8</TD><TD PORT="time_written_size">4</TD><TD>u4le</TD><TD PORT="time_written_type">time_written</TD></TR>
				<TR><TD PORT="event_id_pos">12</TD><TD PORT="event_id_size">4</TD><TD>u4le</TD><TD PORT="event_id_type">event_id</TD></TR>
				<TR><TD PORT="event_type_pos">16</TD><TD PORT="event_type_size">2</TD><TD>u2le?EventTypes</TD><TD PORT="event_type_type">event_type</TD></TR>
				<TR><TD PORT="num_strings_pos">18</TD><TD PORT="num_strings_size">2</TD><TD>u2le</TD><TD PORT="num_strings_type">num_strings</TD></TR>
				<TR><TD PORT="event_category_pos">20</TD><TD PORT="event_category_size">2</TD><TD>u2le</TD><TD PORT="event_category_type">event_category</TD></TR>
				<TR><TD PORT="reserved_pos">22</TD><TD PORT="reserved_size">6</TD><TD></TD><TD PORT="reserved_type">reserved</TD></TR>
				<TR><TD PORT="ofs_strings_pos">28</TD><TD PORT="ofs_strings_size">4</TD><TD>u4le</TD><TD PORT="ofs_strings_type">ofs_strings</TD></TR>
				<TR><TD PORT="len_user_sid_pos">32</TD><TD PORT="len_user_sid_size">4</TD><TD>u4le</TD><TD PORT="len_user_sid_type">len_user_sid</TD></TR>
				<TR><TD PORT="ofs_user_sid_pos">36</TD><TD PORT="ofs_user_sid_size">4</TD><TD>u4le</TD><TD PORT="ofs_user_sid_type">ofs_user_sid</TD></TR>
				<TR><TD PORT="len_data_pos">40</TD><TD PORT="len_data_size">4</TD><TD>u4le</TD><TD PORT="len_data_type">len_data</TD></TR>
				<TR><TD PORT="ofs_data_pos">44</TD><TD PORT="ofs_data_size">4</TD><TD>u4le</TD><TD PORT="ofs_data_type">ofs_data</TD></TR>
			</TABLE>>];
			record_body__inst__user_sid [label=<<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
				<TR><TD BGCOLOR="#E0FFE0">pos</TD><TD BGCOLOR="#E0FFE0">size</TD><TD BGCOLOR="#E0FFE0">type</TD><TD BGCOLOR="#E0FFE0">id</TD></TR>
				<TR><TD PORT="user_sid_pos">(ofs_user_sid - 8)</TD><TD PORT="user_sid_size">len_user_sid</TD><TD></TD><TD PORT="user_sid_type">user_sid</TD></TR>
			</TABLE>>];
			record_body__inst__data [label=<<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
				<TR><TD BGCOLOR="#E0FFE0">pos</TD><TD BGCOLOR="#E0FFE0">size</TD><TD BGCOLOR="#E0FFE0">type</TD><TD BGCOLOR="#E0FFE0">id</TD></TR>
				<TR><TD PORT="data_pos">(ofs_data - 8)</TD><TD PORT="data_size">len_data</TD><TD></TD><TD PORT="data_type">data</TD></TR>
			</TABLE>>];
		}
		subgraph cluster__cursor_record_body {
			label="WindowsEvtLog::CursorRecordBody";
			graph[style=dotted];

			cursor_record_body__seq [label=<<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
				<TR><TD BGCOLOR="#E0FFE0">pos</TD><TD BGCOLOR="#E0FFE0">size</TD><TD BGCOLOR="#E0FFE0">type</TD><TD BGCOLOR="#E0FFE0">id</TD></TR>
				<TR><TD PORT="magic_pos">0</TD><TD PORT="magic_size">12</TD><TD>22 22 22 22 33 33 33 33 44 44 44 44</TD><TD PORT="magic_type">magic</TD></TR>
				<TR><TD PORT="ofs_first_record_pos">12</TD><TD PORT="ofs_first_record_size">4</TD><TD>u4le</TD><TD PORT="ofs_first_record_type">ofs_first_record</TD></TR>
				<TR><TD PORT="ofs_next_record_pos">16</TD><TD PORT="ofs_next_record_size">4</TD><TD>u4le</TD><TD PORT="ofs_next_record_type">ofs_next_record</TD></TR>
				<TR><TD PORT="idx_next_record_pos">20</TD><TD PORT="idx_next_record_size">4</TD><TD>u4le</TD><TD PORT="idx_next_record_type">idx_next_record</TD></TR>
				<TR><TD PORT="idx_first_record_pos">24</TD><TD PORT="idx_first_record_size">4</TD><TD>u4le</TD><TD PORT="idx_first_record_type">idx_first_record</TD></TR>
			</TABLE>>];
		}
	}
	windows_evt_log__seq:header_type -> header__seq [style=bold];
	windows_evt_log__seq:records_type -> record__seq [style=bold];
	header__seq:flags_type -> flags__seq [style=bold];
	record__seq:body_type -> record__seq_body_switch [style=bold];
	record__seq_body_switch:case0 -> record_body__seq [style=bold];
	record__seq_body_switch:case1 -> cursor_record_body__seq [style=bold];
	record__seq:type_type -> record__seq:body_type [color="#404040"];
	record_body__seq:ofs_user_sid_type -> record_body__inst__user_sid:user_sid_pos [color="#404040"];
	record_body__seq:len_user_sid_type -> record_body__inst__user_sid:user_sid_size [color="#404040"];
	record_body__seq:ofs_data_type -> record_body__inst__data:data_pos [color="#404040"];
	record_body__seq:len_data_type -> record_body__inst__data:data_size [color="#404040"];
}