diff --git a/crates/kms/src/api_types.rs b/crates/kms/src/api_types.rs
index 1921ec9de..5a5ac8531 100644
--- a/crates/kms/src/api_types.rs
+++ b/crates/kms/src/api_types.rs
@@ -20,7 +20,7 @@ use crate::config::{
 };
 use crate::service_manager::KmsServiceStatus;
 use crate::types::{KeyMetadata, KeyUsage};
-use serde::{Deserialize, Serialize};
+use serde::{Deserialize, Deserializer, Serialize};
 use std::collections::HashMap;
 use std::fmt;
 use std::path::PathBuf;
@@ -28,6 +28,7 @@ use std::time::Duration;
 
 /// Request to configure KMS with Local backend
 #[derive(Clone, Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
 pub struct ConfigureLocalKmsRequest {
     /// Directory to store key files
     pub key_dir: PathBuf,
@@ -71,10 +72,12 @@ impl fmt::Debug for ConfigureLocalKmsRequest {
 
 /// Request to configure KMS with Vault KV v2 + Transit backend
 #[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
 pub struct ConfigureVaultKmsRequest {
     /// Vault server URL
     pub address: String,
     /// Authentication method
+    #[serde(deserialize_with = "deserialize_strict_vault_auth_method")]
     pub auth_method: VaultAuthMethod,
     /// Vault namespace (Vault Enterprise, optional)
     pub namespace: Option<String>,
@@ -104,10 +107,12 @@ pub struct ConfigureVaultKmsRequest {
 
 /// Request to configure KMS with Vault Transit backend
 #[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
 pub struct ConfigureVaultTransitKmsRequest {
     /// Vault server URL
     pub address: String,
     /// Authentication method
+    #[serde(deserialize_with = "deserialize_strict_vault_auth_method")]
     pub auth_method: VaultAuthMethod,
     /// Vault namespace (Vault Enterprise, optional)
     pub namespace: Option<String>,
@@ -165,11 +170,35 @@ pub struct ConfigureKmsResponse {
 
 /// Request to start KMS service
 #[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
 pub struct StartKmsRequest {
     /// Whether to force start (restart if already running)
     pub force: Option<bool>,
 }
 
+#[derive(Deserialize)]
+#[serde(deny_unknown_fields)]
+enum StrictVaultAuthMethod {
+    Token { token: String },
+    AppRole { role_id: String, secret_id: String },
+}
+
+impl From<StrictVaultAuthMethod> for VaultAuthMethod {
+    fn from(value: StrictVaultAuthMethod) -> Self {
+        match value {
+            StrictVaultAuthMethod::Token { token } => Self::Token { token },
+            StrictVaultAuthMethod::AppRole { role_id, secret_id } => Self::AppRole { role_id, secret_id },
+        }
+    }
+}
+
+fn deserialize_strict_vault_auth_method<'de, D>(deserializer: D) -> Result<VaultAuthMethod, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    StrictVaultAuthMethod::deserialize(deserializer).map(Into::into)
+}
+
 /// KMS start response
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct StartKmsResponse {
@@ -566,6 +595,39 @@ mod tests {
         assert!(request.to_kms_config().validate().is_ok());
     }
 
+    #[test]
+    fn test_configure_request_rejects_unknown_fields() {
+        let raw = serde_json::json!({
+            "backend_type": "local",
+            "key_dir": "./target/kms-key-dir",
+            "unexpected_field": true
+        });
+
+        let err = serde_json::from_value::<ConfigureKmsRequest>(raw).expect_err("unknown configure field should fail");
+        assert!(err.to_string().contains("unknown field"));
+
+        let raw = serde_json::json!({
+            "backend_type": "vault",
+            "address": "http://127.0.0.1:8200",
+            "auth_method": {
+                "Token": {
+                    "token": "dev-root-token",
+                    "unexpected_field": true
+                }
+            }
+        });
+
+        let err = serde_json::from_value::<ConfigureKmsRequest>(raw).expect_err("unknown auth field should fail");
+        assert!(err.to_string().contains("unknown field"));
+    }
+
+    #[test]
+    fn test_start_request_rejects_unknown_fields() {
+        let err = serde_json::from_str::<StartKmsRequest>(r#"{"force":true,"unexpected_field":true}"#)
+            .expect_err("unknown start field should fail");
+        assert!(err.to_string().contains("unknown field"));
+    }
+
     #[test]
     fn test_vault_transit_summary_reports_backend_details() {
         let config = KmsConfig {
diff --git a/rustfs/src/admin/handlers/kms_keys.rs b/rustfs/src/admin/handlers/kms_keys.rs
index 7b5064737..dc61980c7 100644
--- a/rustfs/src/admin/handlers/kms_keys.rs
+++ b/rustfs/src/admin/handlers/kms_keys.rs
@@ -34,6 +34,7 @@ use tracing::{error, info};
 use urlencoding;
 
 #[derive(Debug, Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
 pub struct CreateKmsKeyRequest {
     pub key_usage: Option<KeyUsage>,
     pub description: Option<String>,
@@ -49,6 +50,7 @@ pub struct CreateKmsKeyResponse {
 }
 
 #[derive(Debug, Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
 pub struct CreateKeyApiRequest {
     pub key_usage: Option<KeyUsage>,
     pub description: Option<String>,
@@ -74,6 +76,7 @@ pub struct ListKeysApiResponse {
 }
 
 #[derive(Debug, Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
 pub struct GenerateDataKeyApiRequest {
     pub key_id: String,
     pub key_spec: KeySpec,
@@ -321,6 +324,7 @@ impl Operation for DescribeKeyHandler {
 #[cfg(test)]
 mod tests {
     use super::{
+        CancelKmsKeyDeletionRequest, CreateKeyApiRequest, CreateKmsKeyRequest, DeleteKmsKeyRequest, GenerateDataKeyApiRequest,
         extract_key_id, kms_create_key_actions, kms_delete_key_actions, kms_describe_key_actions, kms_generate_data_key_actions,
         kms_list_keys_actions,
     };
@@ -400,6 +404,23 @@ mod tests {
         assert_has_action(&kms_generate_data_key_actions(), Action::KmsAction(KmsAction::GenerateDataKeyAction));
         assert_has_action(&kms_delete_key_actions(), Action::KmsAction(KmsAction::DeleteKeyAction));
     }
+
+    #[test]
+    fn kms_key_request_bodies_reject_unknown_fields() {
+        let cases = [
+            serde_json::from_str::<CreateKeyApiRequest>(r#"{"unexpected_field":true}"#).map(|_| ()),
+            serde_json::from_str::<CreateKmsKeyRequest>(r#"{"unexpected_field":true}"#).map(|_| ()),
+            serde_json::from_str::<GenerateDataKeyApiRequest>(r#"{"key_id":"key","key_spec":"Aes256","unexpected_field":true}"#)
+                .map(|_| ()),
+            serde_json::from_str::<DeleteKmsKeyRequest>(r#"{"key_id":"key","unexpected_field":true}"#).map(|_| ()),
+            serde_json::from_str::<CancelKmsKeyDeletionRequest>(r#"{"key_id":"key","unexpected_field":true}"#).map(|_| ()),
+        ];
+
+        for result in cases {
+            let err = result.expect_err("unknown KMS key request field should fail");
+            assert!(err.to_string().contains("unknown field"));
+        }
+    }
 }
 
 /// List KMS keys (legacy endpoint)
@@ -650,6 +671,7 @@ impl Operation for CreateKmsKeyHandler {
 }
 
 #[derive(Debug, Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
 pub struct DeleteKmsKeyRequest {
     pub key_id: String,
     pub pending_window_in_days: Option<u32>,
@@ -801,6 +823,7 @@ impl Operation for DeleteKmsKeyHandler {
 }
 
 #[derive(Debug, Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
 pub struct CancelKmsKeyDeletionRequest {
     pub key_id: String,
 }
diff --git a/rustfs/src/admin/handlers/oidc.rs b/rustfs/src/admin/handlers/oidc.rs
index 120bc1636..cf33f5d48 100644
--- a/rustfs/src/admin/handlers/oidc.rs
+++ b/rustfs/src/admin/handlers/oidc.rs
@@ -164,7 +164,7 @@ struct OidcValidationResponse {
 }
 
 #[derive(Debug, Deserialize)]
-#[serde(default)]
+#[serde(default, deny_unknown_fields)]
 struct OidcConfigUpsertRequest {
     enabled: bool,
     display_name: String,
@@ -210,7 +210,7 @@ impl Default for OidcConfigUpsertRequest {
 }
 
 #[derive(Debug, Deserialize)]
-#[serde(default)]
+#[serde(default, deny_unknown_fields)]
 struct OidcConfigValidateRequest {
     provider_id: String,
     enabled: bool,
@@ -1244,6 +1244,26 @@ mod tests {
         assert_eq!(config.roles_claim, OIDC_DEFAULT_ROLES_CLAIM);
     }
 
+    #[test]
+    fn test_oidc_config_upsert_request_rejects_unknown_fields() {
+        let err = serde_json::from_str::<OidcConfigUpsertRequest>(
+            r#"{"config_url":"https://example.com/.well-known/openid-configuration","client_id":"client","unexpected_field":true}"#,
+        )
+        .expect_err("unknown upsert field should fail");
+
+        assert!(err.to_string().contains("unknown field"));
+    }
+
+    #[test]
+    fn test_oidc_config_validate_request_rejects_unknown_fields() {
+        let err = serde_json::from_str::<OidcConfigValidateRequest>(
+            r#"{"provider_id":"default","config_url":"https://example.com/.well-known/openid-configuration","client_id":"client","unexpected_field":true}"#,
+        )
+        .expect_err("unknown validate field should fail");
+
+        assert!(err.to_string().contains("unknown field"));
+    }
+
     #[test]
     fn test_build_provider_config_uses_custom_roles_claim() {
         let req = OidcConfigUpsertRequest {
diff --git a/rustfs/src/admin/handlers/plugins_instances.rs b/rustfs/src/admin/handlers/plugins_instances.rs
index 5fe3bbbc3..8103129f2 100644
--- a/rustfs/src/admin/handlers/plugins_instances.rs
+++ b/rustfs/src/admin/handlers/plugins_instances.rs
@@ -273,12 +273,14 @@ struct ResolvedPluginInstanceTarget {
 }
 
 #[derive(Debug, serde::Deserialize)]
+#[serde(deny_unknown_fields)]
 struct KeyValue {
     key: String,
     value: String,
 }
 
 #[derive(Debug, serde::Deserialize)]
+#[serde(deny_unknown_fields)]
 struct PluginInstanceBody {
     key_values: Vec<KeyValue>,
 }
@@ -852,7 +854,7 @@ impl Operation for DeletePluginInstanceHandler {
 #[cfg(test)]
 mod tests {
     use super::{
-        PluginContractDomain, PluginInstanceFilters, collect_diagnostic_counts, collect_instance_diagnostics,
+        PluginContractDomain, PluginInstanceBody, PluginInstanceFilters, collect_diagnostic_counts, collect_instance_diagnostics,
         extract_plugin_instance_filters, filter_plugin_instances, map_instance, paginate_plugin_instances, parse_bool_filter,
         parse_instance_status, parse_limit_filter, parse_plugin_contract_domain, parse_plugin_instance_diagnostic_code,
         parse_plugin_instance_id, parse_plugin_instance_source, resolve_plugin_instance_target,
@@ -1068,6 +1070,19 @@ mod tests {
         );
     }
 
+    #[test]
+    fn plugin_instance_body_rejects_unknown_fields() {
+        let err = serde_json::from_str::<PluginInstanceBody>(r#"{"key_values":[],"unexpected_field":true}"#)
+            .expect_err("unknown plugin instance body field should fail");
+        assert!(err.to_string().contains("unknown field"));
+
+        let err = serde_json::from_str::<PluginInstanceBody>(
+            r#"{"key_values":[{"key":"endpoint","value":"http://example.com","extra":true}]}"#,
+        )
+        .expect_err("unknown plugin instance key-value field should fail");
+        assert!(err.to_string().contains("unknown field"));
+    }
+
     #[test]
     fn canonical_id_is_stable_and_lowercases_instance_segment() {
         assert_eq!(