[enhancement][filebeat/decode_cef] Add option to ignore missing values

CHANGELOG-developer.next.asciidoc

@@ -196,6 +196,7 @@ The list below covers the major changes between 7.0.0-rc2 and main only.
 - Improve robustness and error reporting from packetbeat default route testing. {pull}39757[39757]
 - Move x-pack/filebeat/input/salesforce jwt import to v5. {pull}39823[39823]
 - Drop x-pack/filebeat/input dependency on github.com/lestrrat-go/jwx/v2. {pull}39968[39968]
+- Added `ignore_empty_values` flag in `decode_cef` Filebeat processor. {pull}40268[40268]
 
 ==== Deprecated
 

CHANGELOG.next.asciidoc

@@ -46,6 +46,7 @@ https://github.com/elastic/beats/compare/v8.8.1\...main[Check the HEAD diff]
 - Fix high IO and handling of a corrupted registry log file. {pull}35893[35893]
 - Filebeat, when running with Elastic-Agent, reports status for Filestream input. {pull}40121[40121]
 - Implement Elastic Agent status and health reporting for Winlog Filebeat input. {pull}40163[40163]
+- Added `ignore_empty_values` flag in `decode_cef` Filebeat processor. {pull}40268[40268]
 
 *Heartbeat*
 

x-pack/filebeat/processors/decode_cef/cef/cef.go

@@ -152,6 +152,13 @@ func (e *Event) Unpack(data string, opts ...Option) error {
 
 		// Mark the data type and do the actual conversion.
 		field.Type = mapping.Type
+
+		if settings.removeEmptyValues && strings.EqualFold(field.String, "") {
+			// Drop the key because the value is empty field.
+			delete(e.Extensions, key)
+			continue
+		}
+
 		field.Interface, err = toType(field.String, mapping.Type, &settings)
 		if err != nil {
 			// Drop the key because the field value is invalid.

x-pack/filebeat/processors/decode_cef/cef/cef_test.go

@@ -58,6 +58,8 @@ const (
 
 	truncatedHeader = "CEF:0|SentinelOne|Mgmt|activityID=1111111111111111111 activityType=3505 siteId=None siteName=None accountId=1222222222222222222 accountName=foo-bar mdr notificationScope=ACCOUNT"
 
+	noValueInExtension = `CEF:26|security|threat=manager|1.0|100|trojan successfully stopped|10|src= dst=12.121.122.82 spt=`
+
 	// Found by fuzzing but minimised by hand.
 	fuzz0 = `CEF:0|a=\\ b|`
 	fuzz1 = `CEF:0|\|a=|b=`
@@ -84,6 +86,7 @@ var testMessages = []string{
 	tabMessage,
 	escapedMessage,
 	truncatedHeader,
+	noValueInExtension,
 	fuzz0,
 	fuzz1,
 	fuzz2,
@@ -161,6 +164,22 @@ func TestEventUnpack(t *testing.T) {
 		}, e.Extensions)
 	})
 
+	t.Run("noValueInExtension", func(t *testing.T) {
+		var e Event
+		err := e.Unpack(noValueInExtension, WithRemoveEmptyValues())
+		assert.NoError(t, err)
+		assert.Equal(t, 26, e.Version)
+		assert.Equal(t, "security", e.DeviceVendor)
+		assert.Equal(t, "threat=manager", e.DeviceProduct)
+		assert.Equal(t, "1.0", e.DeviceVersion)
+		assert.Equal(t, "100", e.DeviceEventClassID)
+		assert.Equal(t, "trojan successfully stopped", e.Name)
+		assert.Equal(t, "10", e.Severity)
+		assert.Equal(t, map[string]*Field{
+			"dst": IPField("12.121.122.82"),
+		}, e.Extensions)
+	})
+
 	t.Run("equalsSignInHeader", func(t *testing.T) {
 		var e Event
 		err := e.Unpack(equalsSignInHeader)

x-pack/filebeat/processors/decode_cef/cef/option.go

@@ -16,8 +16,20 @@ type Option interface {
 // Settings for unpacking messages.
 type Settings struct {
 	fullExtensionNames bool
+	removeEmptyValues  bool
+	timezone           *time.Location
+}
 
-	timezone *time.Location
+type withRemoveEmptyValues struct{}
+
+func (w withRemoveEmptyValues) Apply(s *Settings) {
+	s.removeEmptyValues = true
+}
+
+// WithRemoveEmptyValues causes CEF extension keys without values to be
+// dropped.
+func WithRemoveEmptyValues() Option {
+	return withRemoveEmptyValues{}
 }
 
 type withFullExtensionNames struct{}

x-pack/filebeat/processors/decode_cef/config.go

@@ -7,13 +7,14 @@ package decode_cef
 import "github.com/elastic/beats/v7/libbeat/common/cfgtype"
 
 type config struct {
-	Field         string            `config:"field"`          // Source field containing the CEF message.
-	TargetField   string            `config:"target_field"`   // Target field for the CEF object.
-	IgnoreMissing bool              `config:"ignore_missing"` // Ignore missing source field.
-	IgnoreFailure bool              `config:"ignore_failure"` // Ignore failures when the source field does not contain a CEF message. Parse errors do not cause failures, but are added to error.message.
-	ID            string            `config:"id"`             // Instance ID for debugging purposes.
-	ECS           bool              `config:"ecs"`            // Generate ECS fields.
-	Timezone      *cfgtype.Timezone `config:"timezone"`       // Timezone used when parsing timestamps that do not contain a time zone or offset.
+	Field             string            `config:"field"`               // Source field containing the CEF message.
+	TargetField       string            `config:"target_field"`        // Target field for the CEF object.
+	IgnoreMissing     bool              `config:"ignore_missing"`      // Ignore missing source field.
+	IgnoreFailure     bool              `config:"ignore_failure"`      // Ignore failures when the source field does not contain a CEF message. Parse errors do not cause failures, but are added to error.message.
+	IgnoreEmptyValues bool              `config:"ignore_empty_values"` // Ignore missing values from CEF extension fields.
+	ID                string            `config:"id"`                  // Instance ID for debugging purposes.
+	ECS               bool              `config:"ecs"`                 // Generate ECS fields.
+	Timezone          *cfgtype.Timezone `config:"timezone"`            // Timezone used when parsing timestamps that do not contain a time zone or offset.
 }
 
 func defaultConfig() config {

x-pack/filebeat/processors/decode_cef/decode_cef.go

@@ -88,7 +88,7 @@
 
 	// If the version < 0 after parsing then none of the data is valid so return here.
 	var ce cef.Event
-	if err = ce.Unpack(cefData, cef.WithFullExtensionNames(), cef.WithTimezone(p.Timezone.Location())); ce.Version < 0 && err != nil {
+	if err = ce.Unpack(cefData, cef.WithFullExtensionNames(), cef.WithTimezone(p.Timezone.Location()), cef.WithRemoveEmptyValues()); ce.Version < 0 && err != nil {
 		if p.IgnoreFailure {
 			return event, nil
 		}
@@ -141,7 +141,7 @@
 	return event, nil
 }
 
 //nolint:errcheck // All errors are from mapstr puts.
 func toCEFObject(cefEvent *cef.Event) mapstr.M {
 	// Add CEF header fields.
 	cefObject := mapstr.M{"version": strconv.Itoa(cefEvent.Version)}
@@ -205,7 +205,7 @@
 	}
 }
 
 //nolint:errcheck // All errors are from mapstr puts.
 func appendErrorMessage(m mapstr.M, msg string) error {
 	const field = "error.message"
 	list, _ := m.GetValue(field)

x-pack/filebeat/processors/decode_cef/decode_cef_test.go

@@ -59,6 +59,33 @@ func TestProcessorRun(t *testing.T) {
 				"source.user.name": "admin",
 			},
 		},
+		"empty_field_values": {
+			config: func() config {
+				c := defaultConfig()
+				c.TargetField = ""
+				c.IgnoreEmptyValues = true
+				return c
+			},
+			message: "CEF:1|Trend Micro|Deep Security Manager|1.2.3|600|User Signed In|3|src= suser= target=admin msg=User signed in from 2001:db8::5",
+			fields: mapstr.M{
+				"version":               "1",
+				"device.event_class_id": "600",
+				"device.product":        "Deep Security Manager",
+				"device.vendor":         "Trend Micro",
+				"device.version":        "1.2.3",
+				"name":                  "User Signed In",
+				"severity":              "3",
+				"event.severity":        3,
+				"extensions.message":    "User signed in from 2001:db8::5",
+				"extensions.target":     "admin",
+				// ECS
+				"event.code":       "600",
+				"message":          "User signed in from 2001:db8::5",
+				"observer.product": "Deep Security Manager",
+				"observer.vendor":  "Trend Micro",
+				"observer.version": "1.2.3",
+			},
+		},
 		"parse_errors": {
 			message: "CEF:0|Trend Micro|Deep Security Manager|1.2.3|600|User Signed In|Low|msg=User signed in with =xyz",
 			fields: mapstr.M{

x-pack/filebeat/processors/decode_cef/docs/decode_cef.asciidoc

@@ -37,13 +37,14 @@ The `decode_cef` processor has the following configuration settings.
 .Decode CEF options
 [options="header"]
 |======
-| Name             | Required | Default | Description |
-| `field`          | no       | message | Source field containing the CEF message to be parsed.                        |
-| `target_field`   | no       | cef     | Target field where the parsed CEF object will be written.                    |
-| `ecs`            | no       | true    | Generate Elastic Common Schema (ECS) fields from the CEF data.
-                                          Certain CEF header and extension values will be used to populate ECS fields. |
-| `timezone`       | no       | UTC     | IANA time zone name (e.g. `America/New_York`) or fixed time offset (e.g. `+0200`) to use when parsing times that do not contain a time zone. `Local` may be specified to use the machine's local time zone.|
-| `ignore_missing` | no       | false   | Ignore errors when the source field is missing.                              |
-| `ignore_failure` | no       | false   | Ignore failures when the source field does not contain a CEF message.        |
-| `id`             | no       |         | An identifier for this processor instance. Useful for debugging.             |
+| Name                  | Required | Default | Description |
+| `field`               | no       | message | Source field containing the CEF message to be parsed.                        |
+| `target_field`        | no       | cef     | Target field where the parsed CEF object will be written.                    |
+| `ecs`                 | no       | true    | Generate Elastic Common Schema (ECS) fields from the CEF data.
+                                               Certain CEF header and extension values will be used to populate ECS fields. |
+| `timezone`            | no       | UTC     | IANA time zone name (e.g. `America/New_York`) or fixed time offset (e.g. `+0200`) to use when parsing times that do not contain a time zone. `Local` may be specified to use the machine's local time zone.|
+| `ignore_missing`      | no       | false   | Ignore errors when the source field is missing.                              |
+| `ignore_failure`      | no       | false   | Ignore failures when the source field does not contain a CEF message.        |
+| `ignore_empty_values` | no       | false   | Ignore fields with empty values in the CEF Extensions. (ex. ...src= port=...)|
+| `id`                  | no       |         | An identifier for this processor instance. Useful for debugging.             |
 |======