diff --git a/pkg/leakybucket/bench_race_test.go b/pkg/leakybucket/bench_race_test.go
new file mode 100644
index 00000000000..c59654799ae
--- /dev/null
+++ b/pkg/leakybucket/bench_race_test.go
@@ -0,0 +1,152 @@
+package leakybucket
+
+import (
+	"fmt"
+	"testing"
+	"time"
+
+	log "github.com/sirupsen/logrus"
+
+	"github.com/crowdsecurity/crowdsec/pkg/pipeline"
+)
+
+// benchEvent returns a fresh, realistic parsed HTTP event. Meta is a single map
+// that PourItemToHolders will share (by reference) across every matching bucket.
+func benchEvent(now time.Time) pipeline.Event {
+	return pipeline.Event{
+		Time: now,
+		Meta: map[string]string{
+			"source_ip":       "1.2.3.4",
+			"service":         "http",
+			"log_type":        "http_access-log",
+			"http_status":     "404",
+			"http_path":       "/wp-admin/",
+			"http_verb":       "GET",
+			"http_user_agent": "curl/8.0",
+			"http_host":       "example.com",
+			"machine":         "test",
+			"datasource_path": "/var/log/traefik/access.log",
+			"datasource_type": "file",
+			"k1":              "v1",
+			"k2":              "v2",
+			"k3":              "v3",
+		},
+	}
+}
+
+// runPourBenchmark drives PourItemToHolders against `readers` trigger scenarios
+// (each overflows immediately and reads evt.Meta while building its alert). If
+// withWriter is true, a final scenario whose filter mutates the shared event via
+// evt.SetMeta(...) is appended — reproducing the crowdsecurity/http-technology-probing
+// side effect and the crowdsecurity/crowdsec#4459 data race.
+func runPourBenchmark(b *testing.B, readers int, withWriter bool) {
+	b.Helper()
+
+	// keep the overflow alert validation noise out of the benchmark output
+	oldLevel := log.GetLevel()
+	log.SetLevel(log.PanicLevel)
+	defer log.SetLevel(oldLevel)
+
+	// response collects overflows emitted by every bucket (AllOut). It must be
+	// drained continuously, otherwise the overflowing trigger goroutines block
+	// on the send *after* having read the shared map.
+	response := make(chan pipeline.Event, 4096)
+
+	stop := make(chan struct{})
+	go func() {
+		for {
+			select {
+			case <-stop:
+				return
+			case <-response:
+			}
+		}
+	}()
+	defer close(stop)
+
+	holders := make([]BucketFactory, 0, readers+1)
+
+	// Readers: each is a trigger that overflows immediately and reads evt.Meta
+	// while building the alert.
+	for i := range readers {
+		holders = append(holders, BucketFactory{
+			Spec: BucketSpec{
+				Name:        fmt.Sprintf("reader_%d", i),
+				Description: "reads shared Meta on overflow",
+				Type:        "trigger",
+				Filter:      "true",
+			},
+		})
+	}
+
+	if withWriter {
+		// The writer last: its filter has a side effect on the shared event, just
+		// like crowdsecurity/http-technology-probing's `evt.SetMeta(...)`.
+		holders = append(holders, BucketFactory{
+			Spec: BucketSpec{
+				Name:        "writer",
+				Description: "mutates shared Meta from its filter",
+				Type:        "trigger",
+				Filter:      `evt.SetMeta("injected", "1")`,
+			},
+		})
+	}
+
+	for idx := range holders {
+		holders[idx].ret = response
+		if err := holders[idx].LoadBucket(); err != nil {
+			b.Fatalf("while loading holder %d: %s", idx, err)
+		}
+
+		if err := holders[idx].Validate(); err != nil {
+			b.Fatalf("while validating holder %d: %s", idx, err)
+		}
+	}
+
+	ctx := b.Context()
+	bucketStore := NewBucketStore()
+	now := time.Now().UTC()
+
+	for b.Loop() {
+		evt := benchEvent(now)
+		if _, err := PourItemToHolders(ctx, evt, holders, bucketStore, nil); err != nil {
+			b.Fatalf("while pouring item: %s", err)
+		}
+	}
+}
+
+// BenchmarkPourSharedMetaRace reproduces the data race reported in
+// crowdsecurity/crowdsec#4459.
+//
+// Root cause: PourItemToHolders pours a single parsed event into every matching
+// scenario, but Event.Meta is a map (reference type) and the pour path only
+// makes a shallow struct copy (pipeline.Queue.Add). Every bucket queue across
+// all matching scenarios therefore ends up sharing the *same* Meta map.
+//
+// It wires up several "reader" trigger scenarios followed by a "writer" whose
+// filter mutates the shared map via evt.SetMeta(...). When runPour evaluates the
+// writer's filter (a map write) while an already-poured reader bucket iterates
+// the same map during overflow (a map read), the Go runtime aborts with:
+//
+//	fatal error: concurrent map iteration and map write
+//	fatal error: concurrent map read and map write
+//
+// Run as a race reproducer (reports a data race before the fix, clean after):
+//
+//	go test -tags 'netgo,osusergo,expr_debug,nomsgpack' -race \
+//	    -run='^$' -bench=BenchmarkPourSharedMetaRace ./pkg/leakybucket/
+func BenchmarkPourSharedMetaRace(b *testing.B) {
+	runPourBenchmark(b, 8, true)
+}
+
+// BenchmarkPourNoSideEffect is the same pour workload without the side-effecting
+// filter, so no map is ever mutated after being poured. It is race-free both
+// before and after the #4459 fix, which makes it the apples-to-apples way to
+// measure the fix's only cost: the per-pour CopyForBucket clone. Compare ns/op
+// and allocs/op with and without the fix applied:
+//
+//	go test -tags 'netgo,osusergo,expr_debug,nomsgpack' \
+//	    -run='^$' -bench=BenchmarkPourNoSideEffect -benchmem ./pkg/leakybucket/
+func BenchmarkPourNoSideEffect(b *testing.B) {
+	runPourBenchmark(b, 8, false)
+}
diff --git a/pkg/leakybucket/manager_run.go b/pkg/leakybucket/manager_run.go
index 1a5f0218f3d..943d0118fef 100644
--- a/pkg/leakybucket/manager_run.go
+++ b/pkg/leakybucket/manager_run.go
@@ -74,6 +74,12 @@ func PourItemToBucket(
 	var buckey = bucket.Mapkey
 	var err error
 
+	// Make a copy of the various maps for this bucket
+	// Otherwise, we could risk reading and writing to the same map concurrently
+	// (eg, with a call to evt.SetMeta in a filter, which the same event has lead to an overflow for another bucket)
+	localEvt := parsed.CopyForBucket()
+	parsed = &localEvt
+
 	sigclosed := 0
 	failed_sent := 0
 	attempts := 0
diff --git a/pkg/pipeline/event.go b/pkg/pipeline/event.go
index ce61893f482..ec56e96bd03 100644
--- a/pkg/pipeline/event.go
+++ b/pkg/pipeline/event.go
@@ -1,6 +1,7 @@
 package pipeline
 
 import (
+	"maps"
 	"net/netip"
 	"time"
 
@@ -45,6 +46,16 @@ type Event struct {
 	Meta map[string]string `json:"Meta,omitempty" yaml:"Meta,omitempty"`
 }
 
+func (e *Event) CopyForBucket() Event {
+	out := *e
+	out.Parsed = maps.Clone(e.Parsed)
+	out.Enriched = maps.Clone(e.Enriched)
+	out.Unmarshaled = maps.Clone(e.Unmarshaled)
+	out.Meta = maps.Clone(e.Meta)
+
+	return out
+}
+
 func MakeEvent(timeMachine bool, evtType int, process bool) Event {
 	evt := Event{
 		Parsed:      make(map[string]string),
diff --git a/pkg/pipeline/event_copy_test.go b/pkg/pipeline/event_copy_test.go
new file mode 100644
index 00000000000..c84ac817574
--- /dev/null
+++ b/pkg/pipeline/event_copy_test.go
@@ -0,0 +1,70 @@
+package pipeline
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestCopyForBucketIndependence(t *testing.T) {
+	src := Event{
+		Meta:        map[string]string{"source_ip": "1.2.3.4", "log_type": "http_access-log"},
+		Parsed:      map[string]string{"verb": "GET"},
+		Enriched:    map[string]string{"IsoCode": "FR"},
+		Unmarshaled: map[string]any{"json": map[string]any{"a": 1}},
+	}
+
+	cp := src.CopyForBucket()
+
+	// same content right after the copy
+	assert.Equal(t, src.Meta, cp.Meta)
+	assert.Equal(t, src.Parsed, cp.Parsed)
+	assert.Equal(t, src.Enriched, cp.Enriched)
+
+	// mutating the copy must not affect the source (this is the #4459 guarantee)
+	cp.SetMeta("injected", "1")
+	cp.SetParsed("verb", "POST")
+	cp.Enriched["IsoCode"] = "US"
+
+	_, ok := src.Meta["injected"]
+	assert.False(t, ok, "writing copy.Meta leaked into source")
+	assert.Equal(t, "GET", src.Parsed["verb"], "writing copy.Parsed leaked into source")
+	assert.Equal(t, "FR", src.Enriched["IsoCode"], "writing copy.Enriched leaked into source")
+
+	// the top-level Unmarshaled map is cloned (key add/remove is isolated)
+	cp.Unmarshaled["new"] = 2
+	_, ok = src.Unmarshaled["new"]
+	assert.False(t, ok, "adding a key to copy.Unmarshaled leaked into source")
+}
+
+func TestCopyForBucketNilMapsStayNil(t *testing.T) {
+	var src Event
+
+	cp := src.CopyForBucket()
+
+	// maps.Clone preserves nil, which the downstream nil checks rely on
+	require.Nil(t, cp.Meta)
+	require.Nil(t, cp.Parsed)
+	require.Nil(t, cp.Enriched)
+	require.Nil(t, cp.Unmarshaled)
+}
+
+// BenchmarkCopyForBucket isolates the per-pour cost of the #4459 fix: cloning
+// the four data maps of a realistic parsed HTTP event.
+func BenchmarkCopyForBucket(b *testing.B) {
+	src := Event{
+		Meta: map[string]string{
+			"source_ip": "1.2.3.4", "service": "http", "log_type": "http_access-log",
+			"http_status": "404", "http_path": "/wp-admin/", "http_verb": "GET",
+			"http_user_agent": "curl/8.0", "http_host": "example.com", "machine": "test",
+			"datasource_path": "/var/log/traefik/access.log", "datasource_type": "file",
+		},
+		Parsed:   map[string]string{"verb": "GET", "status": "404", "request": "/wp-admin/"},
+		Enriched: map[string]string{"IsoCode": "FR", "ASNumber": "1234", "ASNOrg": "Example"},
+	}
+
+	for b.Loop() {
+		_ = src.CopyForBucket()
+	}
+}