diff --git a/staging/src/k8s.io/apiserver/pkg/apis/apiserver/validation/validation.go b/staging/src/k8s.io/apiserver/pkg/apis/apiserver/validation/validation.go
index 0b781e718dd..bed40faac29 100644
--- a/staging/src/k8s.io/apiserver/pkg/apis/apiserver/validation/validation.go
+++ b/staging/src/k8s.io/apiserver/pkg/apis/apiserver/validation/validation.go
@@ -355,6 +355,11 @@ func validateClaimMappings(compiler authenticationcel.Compiler, state *validatio
 		if mapping.Key != strings.ToLower(mapping.Key) {
 			allErrs = append(allErrs, field.Invalid(fldPath.Child("key"), mapping.Key, "key must be lowercase"))
 		}
+
+		if isKubernetesDomainPrefix(mapping.Key) {
+			allErrs = append(allErrs, field.Invalid(fldPath.Child("key"), mapping.Key, "k8s.io, kubernetes.io and their subdomains are reserved for Kubernetes use"))
+		}
+
 		if seenExtraKeys.Has(mapping.Key) {
 			allErrs = append(allErrs, field.Duplicate(fldPath.Child("key"), mapping.Key))
 			continue
@@ -394,6 +399,24 @@ func validateClaimMappings(compiler authenticationcel.Compiler, state *validatio
 	return allErrs
 }
 
+func isKubernetesDomainPrefix(key string) bool {
+	domainPrefix := getDomainPrefix(key)
+	if domainPrefix == "kubernetes.io" || strings.HasSuffix(domainPrefix, ".kubernetes.io") {
+		return true
+	}
+	if domainPrefix == "k8s.io" || strings.HasSuffix(domainPrefix, ".k8s.io") {
+		return true
+	}
+	return false
+}
+
+func getDomainPrefix(key string) string {
+	if parts := strings.SplitN(key, "/", 2); len(parts) == 2 {
+		return parts[0]
+	}
+	return ""
+}
+
 func usesEmailClaim(ast *celgo.Ast) bool {
 	return hasSelectExp(ast.Expr(), "claims", "email")
 }
diff --git a/staging/src/k8s.io/apiserver/pkg/apis/apiserver/validation/validation_test.go b/staging/src/k8s.io/apiserver/pkg/apis/apiserver/validation/validation_test.go
index 61778590bc8..deba4617c1e 100644
--- a/staging/src/k8s.io/apiserver/pkg/apis/apiserver/validation/validation_test.go
+++ b/staging/src/k8s.io/apiserver/pkg/apis/apiserver/validation/validation_test.go
@@ -1363,6 +1363,69 @@ func TestValidateClaimMappings(t *testing.T) {
 			structuredAuthnFeatureEnabled: true,
 			want:                          `issuer.claimMappings.extra[0].key: Invalid value: "example.org/Foo": key must be lowercase`,
 		},
+		{
+			name: "extra mapping key prefix is k8.io",
+			in: api.ClaimMappings{
+				Username: api.PrefixedClaimOrExpression{Expression: "claims.username"},
+				Groups:   api.PrefixedClaimOrExpression{Expression: "claims.groups"},
+				Extra: []api.ExtraMapping{
+					{Key: "k8s.io/foo", ValueExpression: "claims.extra"},
+				},
+			},
+			structuredAuthnFeatureEnabled: true,
+			want:                          `issuer.claimMappings.extra[0].key: Invalid value: "k8s.io/foo": k8s.io, kubernetes.io and their subdomains are reserved for Kubernetes use`,
+		},
+		{
+			name: "extra mapping key prefix contains k8.io",
+			in: api.ClaimMappings{
+				Username: api.PrefixedClaimOrExpression{Expression: "claims.username"},
+				Groups:   api.PrefixedClaimOrExpression{Expression: "claims.groups"},
+				Extra: []api.ExtraMapping{
+					{Key: "example.k8s.io/foo", ValueExpression: "claims.extra"},
+				},
+			},
+			structuredAuthnFeatureEnabled: true,
+			want:                          `issuer.claimMappings.extra[0].key: Invalid value: "example.k8s.io/foo": k8s.io, kubernetes.io and their subdomains are reserved for Kubernetes use`,
+		},
+		{
+			name: "extra mapping key prefix is kubernetes.io",
+			in: api.ClaimMappings{
+				Username: api.PrefixedClaimOrExpression{Expression: "claims.username"},
+				Groups:   api.PrefixedClaimOrExpression{Expression: "claims.groups"},
+				Extra: []api.ExtraMapping{
+					{Key: "kubernetes.io/foo", ValueExpression: "claims.extra"},
+				},
+			},
+			structuredAuthnFeatureEnabled: true,
+			want:                          `issuer.claimMappings.extra[0].key: Invalid value: "kubernetes.io/foo": k8s.io, kubernetes.io and their subdomains are reserved for Kubernetes use`,
+		},
+		{
+			name: "extra mapping key prefix contains kubernetes.io",
+			in: api.ClaimMappings{
+				Username: api.PrefixedClaimOrExpression{Expression: "claims.username"},
+				Groups:   api.PrefixedClaimOrExpression{Expression: "claims.groups"},
+				Extra: []api.ExtraMapping{
+					{Key: "example.kubernetes.io/foo", ValueExpression: "claims.extra"},
+				},
+			},
+			structuredAuthnFeatureEnabled: true,
+			want:                          `issuer.claimMappings.extra[0].key: Invalid value: "example.kubernetes.io/foo": k8s.io, kubernetes.io and their subdomains are reserved for Kubernetes use`,
+		},
+		{
+			name: "extra mapping key prefix with ak8s.io, *.ak8s.io, bkubernetes.io, *.bkubernetes.io are still valid",
+			in: api.ClaimMappings{
+				Username: api.PrefixedClaimOrExpression{Expression: "claims.username"},
+				Groups:   api.PrefixedClaimOrExpression{Expression: "claims.groups"},
+				Extra: []api.ExtraMapping{
+					{Key: "ak8s.io/foo", ValueExpression: "claims.extra"},
+					{Key: "example.ak8s.io/foo", ValueExpression: "claims.extra"},
+					{Key: "bkubernetes.io/foo", ValueExpression: "claims.extra"},
+					{Key: "example.bkubernetes.io/foo", ValueExpression: "claims.extra"},
+				},
+			},
+			structuredAuthnFeatureEnabled: true,
+			want:                          "",
+		},
 		{
 			name: "valid claim mappings but uses email without verification",
 			in: api.ClaimMappings{