diff --git a/cmd/tls/handlers/osctrld_limits.go b/cmd/tls/handlers/osctrld_limits.go
index b856c5f1..8954607f 100644
--- a/cmd/tls/handlers/osctrld_limits.go
+++ b/cmd/tls/handlers/osctrld_limits.go
@@ -16,6 +16,10 @@ import (
 // a spray from many addresses cannot flood audit_logs.
 const osctrldAuditPerHour = 60
 
+// osctrldUnknownEnv stands in for every environment in a path that does
+// not resolve, so made-up UUIDs share one audit cap and one metric label.
+const osctrldUnknownEnv = "<unknown>"
+
 // OsctrldLimits holds the per-process rate limiters of the osctrld routes.
 // They key on utils.GetIP: the TCP peer, or the forwarded client when the
 // peer is a configured trusted proxy (otherwise every client behind a proxy
@@ -127,18 +131,16 @@ func (h *HandlersTLS) osctrldAudit(ip string, env environments.TLSEnvironment, r
 	h.AuditLog.FailedOsctrld(ip, env.Name, reason, env.ID)
 }
 
-// osctrldAuditEnv resolves the environment in the path for an audit entry,
-// falling back to the (UUID-validated) path value with no ID.
+// osctrldAuditEnv resolves the environment in the path for an audit entry.
+// Any path that does not resolve maps to the osctrldUnknownEnv sentinel
+// (ID 0), so it shares one audit cap, audit environment and metric label.
 func (h *HandlersTLS) osctrldAuditEnv(r *http.Request, envVar string) environments.TLSEnvironment {
 	if h.EnvCache != nil {
 		if env, err := h.EnvCache.GetByUUID(r.Context(), strings.ToLower(envVar)); err == nil {
 			return env
 		}
 	}
-	if !utils.CheckUUID(envVar) {
-		envVar = "<invalid>"
-	}
-	return environments.TLSEnvironment{UUID: envVar, Name: envVar}
+	return environments.TLSEnvironment{UUID: osctrldUnknownEnv, Name: osctrldUnknownEnv}
 }
 
 // osctrldSecret checks the secret of an osctrld request. The budget check,
diff --git a/cmd/tls/handlers/osctrld_limits_test.go b/cmd/tls/handlers/osctrld_limits_test.go
index 2567108a..0e98f0bb 100644
--- a/cmd/tls/handlers/osctrld_limits_test.go
+++ b/cmd/tls/handlers/osctrld_limits_test.go
@@ -3,6 +3,7 @@ package handlers
 import (
 	"bytes"
 	"encoding/json"
+	"fmt"
 	"net/http"
 	"net/http/httptest"
 	"strconv"
@@ -14,6 +15,7 @@ import (
 	"github.com/jmpsec/osctrl/pkg/auditlog"
 	"github.com/jmpsec/osctrl/pkg/config"
 	"github.com/jmpsec/osctrl/pkg/environments"
+	"github.com/jmpsec/osctrl/pkg/ratelimit"
 	"github.com/jmpsec/osctrl/pkg/utils"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/stretchr/testify/require"
@@ -368,3 +370,35 @@ func TestOsctrldBlockedAuditResolvesUpperCaseEnv(t *testing.T) {
 	require.Equal(t, f.env.ID, row.EnvironmentID)
 	require.Contains(t, row.Line, f.env.Name)
 }
+
+// Blocked rejections for environments that do not resolve all share one
+// "<unknown>" audit cap, audit environment and metric label, however many
+// made-up UUIDs are used. Known environments keep their own.
+func TestOsctrldUnknownEnvsShareAuditCap(t *testing.T) {
+	cfg := config.DefaultRateLimits()
+	cfg.OsctrldAuth.Burst = 1
+	cfg.OsctrldAuth.MaxBuckets = 1
+	f := newOsctrldFixture(t, cfg)
+	f.h.OsctrldLimits.authAudit = ratelimit.New(1, time.Hour, 2*time.Hour)
+	// Fill the map, then spend the shared overflow budget.
+	require.Equal(t, http.StatusForbidden, f.cert("198.51.100.1", f.env, "wrong"))
+	require.Equal(t, http.StatusForbidden, f.cert("198.51.100.2", f.env, "wrong"))
+	dropped := osctrldAuthAuditDropped.WithLabelValues(osctrldUnknownEnv)
+	before := metricValue(t, dropped)
+	for i := 0; i < 70; i++ {
+		unknown := environments.TLSEnvironment{UUID: fmt.Sprintf("%08d-1111-4111-8111-111111111111", i)}
+		require.Equal(t, http.StatusTooManyRequests, f.cert("203.0.113."+strconv.Itoa(i), unknown, "wrong"))
+	}
+	var rows []auditlog.AuditLog
+	require.NoError(t, f.db.Where("environment_id = ?", 0).Find(&rows).Error)
+	require.Len(t, rows, osctrldAuditPerHour)
+	for _, row := range rows {
+		require.Contains(t, row.Line, "env "+osctrldUnknownEnv+":")
+	}
+	require.Equal(t, before+70-osctrldAuditPerHour, metricValue(t, dropped))
+	// The known environment's audits were not touched by the unknown cap.
+	var known int64
+	require.NoError(t, f.db.Model(&auditlog.AuditLog{}).Where("environment_id = ?", f.env.ID).Count(&known).Error)
+	require.EqualValues(t, 2, known)
+	require.Equal(t, f.env.Name, f.h.osctrldAuditEnv(httptest.NewRequest(http.MethodPost, "/", nil), f.env.UUID).Name)
+}