fix(replication): deny non-owner replication config edits under site replication

Under site replication a user holding only bucket-scoped
s3:PutReplicationConfiguration could rewrite or erase the operator-managed
site-repl-* rules, with the change broadcast to every peer (backlog#1948,
audit A1/P2-17).

- Gate PutBucketReplication/DeleteBucketReplication in the S3 handlers:
  when site replication is enabled and the requester is not the owner,
  return MinIO-parity XMinioReplicationDenyEdit (HTTP 400). The gate runs
  after policy authorization and only on the external S3 path; the
  reconciler and peer bucket-meta ingestion are unaffected.
- Defense in depth in the bucket usecase: PUT merges the incoming config
  with the stored site-repl-* rules (same merge as peer ingestion) instead
  of overwriting verbatim; DELETE keeps the site-repl-* rules and never
  garbage-collects a bucket target a surviving site-replication rule still
  references.
- Move is_site_replication_rule / merge_incoming_replication_config /
  replication_target_arn_deployment_id from the admin site-replication
  handler down to rustfs-replication so the app layer can reuse them
  without new layering violations.

crates/ecstore/src/api/mod.rs

@@ -199,12 +199,12 @@ pub mod bucket {
             VersionPurgeStatusType, XferStats, commit_force_delete_intent, complete_force_delete_intent,
             delete_replication_state_from_config, delete_replication_version_id, get_global_replication_pool,
             get_global_replication_stats, get_proxy_targets, init_background_replication,
-            invalid_replication_config_status_field, persist_force_delete_intent, read_durable_mrf_backlog,
-            replication_state_to_filemeta, replication_status_to_filemeta, replication_statuses_map, replication_target_arns,
-            resync_start_conflict_id, should_remove_replication_target, should_schedule_delete_replication,
-            should_use_existing_delete_replication_info, should_use_existing_delete_replication_source,
-            unsupported_replication_config_field, validate_replication_config_structure, validate_replication_config_target_arns,
-            version_purge_status_to_filemeta,
+            invalid_replication_config_status_field, is_site_replication_rule, merge_incoming_replication_config,
+            persist_force_delete_intent, read_durable_mrf_backlog, replication_state_to_filemeta, replication_status_to_filemeta,
+            replication_statuses_map, replication_target_arn_deployment_id, replication_target_arns, resync_start_conflict_id,
+            should_remove_replication_target, should_schedule_delete_replication, should_use_existing_delete_replication_info,
+            should_use_existing_delete_replication_source, unsupported_replication_config_field,
+            validate_replication_config_structure, validate_replication_config_target_arns, version_purge_status_to_filemeta,
         };
     }
 

crates/ecstore/src/bucket/replication/mod.rs

@@ -47,7 +47,8 @@ pub use replication_config_boundary::{
     ObjectOpts, REMOTE_TARGET_CAPABILITY_CONTRACT_VERSION, REMOTE_TARGET_UNSUPPORTED_FIELDS, REMOTE_TARGET_WRITABLE_FIELDS,
     REPLICATION_CAPABILITY_CONTRACT_VERSION, REPLICATION_READ_ONLY_HISTORICAL_FIELDS, REPLICATION_WRITABLE_FIELDS,
     ReplicationConfigStructureError, ReplicationConfigurationExt, ReplicationTargetValidationError,
-    invalid_replication_config_status_field, replication_target_arns, should_remove_replication_target,
+    invalid_replication_config_status_field, is_site_replication_rule, merge_incoming_replication_config,
+    replication_target_arn_deployment_id, replication_target_arns, should_remove_replication_target,
     unsupported_replication_config_field, validate_replication_config_structure, validate_replication_config_target_arns,
 };
 pub(crate) use replication_filemeta_boundary::version_purge_statuses_map;

crates/ecstore/src/bucket/replication/replication_config_boundary.rs

@@ -16,6 +16,7 @@ pub use rustfs_replication::{
     ObjectOpts, REMOTE_TARGET_CAPABILITY_CONTRACT_VERSION, REMOTE_TARGET_UNSUPPORTED_FIELDS, REMOTE_TARGET_WRITABLE_FIELDS,
     REPLICATION_CAPABILITY_CONTRACT_VERSION, REPLICATION_READ_ONLY_HISTORICAL_FIELDS, REPLICATION_WRITABLE_FIELDS,
     ReplicationConfigStructureError, ReplicationConfigurationExt, ReplicationRuleExt, ReplicationTargetValidationError,
-    invalid_replication_config_status_field, replication_target_arns, should_remove_replication_target,
+    invalid_replication_config_status_field, is_site_replication_rule, merge_incoming_replication_config,
+    replication_target_arn_deployment_id, replication_target_arns, should_remove_replication_target,
     unsupported_replication_config_field, validate_replication_config_structure, validate_replication_config_target_arns,
 };

crates/replication/src/config.rs

@@ -265,6 +265,78 @@ pub fn active_replication_rule_destination_arns(config: &ReplicationConfiguratio
     arns
 }
 
+/// Deployment id extracted from a site-replication target ARN
+/// (`arn:{rustfs|minio}:replication::<deployment-id>:<bucket>`), or `None`
+/// for an operator-authored ARN.
+pub fn replication_target_arn_deployment_id(arn: &str) -> Option<String> {
+    let parts: Vec<_> = arn.split(':').collect();
+    if parts.len() == 6
+        && parts[0] == "arn"
+        && matches!(parts[1], "rustfs" | "minio")
+        && parts[2] == "replication"
+        && !parts[4].is_empty()
+    {
+        return Some(parts[4].to_string());
+    }
+
+    None
+}
+
+/// Whether `rule` is a site-replication rule (`site-repl-*` id) owned by the
+/// local site's reconciler rather than authored by an operator.
+pub fn is_site_replication_rule(rule: &ReplicationRule) -> bool {
+    rule.id.as_deref().is_some_and(|id| id.starts_with("site-repl-"))
+}
+
+/// Merge an incoming replication config into the local one.
+///
+/// `site-repl-*` rules encode the *holder's* outbound direction — their
+/// destination ARN names another site — so applying an external rule set
+/// verbatim replaces the local reverse rule with one this site can never
+/// satisfy (no bucket target backs it) and replication silently stops. Only
+/// operator-authored rules travel: the site-replication peer ingestion path
+/// and the S3 put/delete-bucket-replication path both keep the local site's
+/// `site-repl-*` rules through this merge. `incoming == None` models a
+/// delete of the operator-authored rules.
+pub fn merge_incoming_replication_config(
+    incoming: Option<ReplicationConfiguration>,
+    local: Option<ReplicationConfiguration>,
+) -> Option<ReplicationConfiguration> {
+    let incoming_role = incoming.as_ref().map(|config| config.role.clone()).unwrap_or_default();
+    // Operator rules first, then the local site rules — the same order the
+    // site-replication reconciler produces, so its no-op check matches and
+    // the bucket metadata is written once per broadcast, not twice.
+    let mut rules: Vec<ReplicationRule> = incoming
+        .into_iter()
+        .flat_map(|config| config.rules)
+        .filter(|rule| !is_site_replication_rule(rule))
+        .collect();
+    rules.extend(
+        local
+            .into_iter()
+            .flat_map(|config| config.rules)
+            .filter(is_site_replication_rule),
+    );
+
+    if rules.is_empty() {
+        return None;
+    }
+
+    for (index, rule) in rules.iter_mut().enumerate() {
+        rule.priority = Some(i32::try_from(index + 1).unwrap_or(i32::MAX));
+    }
+
+    // A site-replication ARN in `role` is the sender's, and the reconciler's
+    // per-peer target lookup reads it — carrying it over would pin the
+    // receiver's targets to the sender's identity.
+    let role = match replication_target_arn_deployment_id(&incoming_role) {
+        Some(_) => String::new(),
+        None => incoming_role,
+    };
+
+    Some(ReplicationConfiguration { role, rules })
+}
+
 pub fn replication_target_arns(config: &ReplicationConfiguration) -> HashSet<String> {
     let role = config.role.trim();
     if !role.is_empty() {

crates/replication/src/lib.rs

@@ -32,7 +32,8 @@ pub use config::{
     ObjectOpts, REMOTE_TARGET_CAPABILITY_CONTRACT_VERSION, REMOTE_TARGET_UNSUPPORTED_FIELDS, REMOTE_TARGET_WRITABLE_FIELDS,
     REPLICATION_CAPABILITY_CONTRACT_VERSION, REPLICATION_READ_ONLY_HISTORICAL_FIELDS, REPLICATION_WRITABLE_FIELDS,
     ReplicationConfigStructureError, ReplicationConfigurationExt, ReplicationTargetValidationError,
-    active_replication_rule_destination_arns, invalid_replication_config_status_field, replication_target_arns,
+    active_replication_rule_destination_arns, invalid_replication_config_status_field, is_site_replication_rule,
+    merge_incoming_replication_config, replication_target_arn_deployment_id, replication_target_arns,
     should_remove_replication_target, unsupported_replication_config_field, validate_replication_config_structure,
     validate_replication_config_target_arns,
 };

rustfs/src/admin/handlers/site_replication.rs

@@ -31,6 +31,9 @@ use crate::admin::storage_api::bucket::metadata::{
 use crate::admin::storage_api::bucket::metadata_sys;
 use crate::admin::storage_api::bucket::quota::BucketQuota;
 use crate::admin::storage_api::bucket::replication;
+use crate::admin::storage_api::bucket::replication::{
+    is_site_replication_rule, merge_incoming_replication_config, replication_target_arn_deployment_id,
+};
 use crate::admin::storage_api::bucket::target::{ARN, BucketTarget, BucketTargetType, BucketTargets, Credentials};
 use crate::admin::storage_api::bucket::target_sys::BucketTargetSys;
 use crate::admin::storage_api::bucket::utils::{deserialize, serialize};
@@ -1117,6 +1120,14 @@ async fn load_site_replication_state() -> S3Result<SiteReplicationState> {
     }
 }
 
+/// Whether this deployment participates in site replication (two or more
+/// peers in the persisted state). Read by the S3 interface layer to gate
+/// replication-config edits (MinIO `ErrReplicationDenyEditError` semantics,
+/// issue #1948); a state-read failure propagates so the gate fails closed.
+pub(crate) async fn site_replication_enabled() -> S3Result<bool> {
+    Ok(load_site_replication_state().await?.enabled())
+}
+
 async fn load_site_replication_state_no_lock(store: Arc<ECStore>) -> S3Result<SiteReplicationState> {
     match read_config_no_lock(store, SITE_REPLICATION_STATE_PATH).await {
         Ok(data) => parse_site_replication_state(&data),
@@ -7748,20 +7759,6 @@ fn bucket_target_deployment_id(target: &BucketTarget) -> Option<String> {
     replication_target_arn_deployment_id(&target.arn)
 }
 
-fn replication_target_arn_deployment_id(arn: &str) -> Option<String> {
-    let parts: Vec<_> = arn.split(':').collect();
-    if parts.len() == 6
-        && parts[0] == "arn"
-        && matches!(parts[1], "rustfs" | "minio")
-        && parts[2] == "replication"
-        && !parts[4].is_empty()
-    {
-        return Some(parts[4].to_string());
-    }
-
-    None
-}
-
 fn prune_removed_site_replication_bucket_targets(
     existing: BucketTargets,
     removed_deployment_ids: &HashSet<String>,
@@ -7786,10 +7783,6 @@ fn prune_removed_site_replication_bucket_targets(
     (BucketTargets { targets }, removed)
 }
 
-fn is_site_replication_rule(rule: &ReplicationRule) -> bool {
-    rule.id.as_deref().is_some_and(|id| id.starts_with("site-repl-"))
-}
-
 /// Whether every `site-repl-*` rule on this bucket resolves to a live remote target.
 ///
 /// The rule set alone cannot answer this: a rule can be perfectly formed while the endpoint
@@ -7815,52 +7808,6 @@ async fn site_replication_targets_online(bucket: &str, replication_config_xml: &
     true
 }
 
-/// Merge a peer's replication config into the local one.
-///
-/// `site-repl-*` rules encode the *sender's* outbound direction — their destination ARN
-/// names the receiver — so applying a peer's rule set verbatim replaces the receiver's
-/// reverse rule with one pointing at itself. No bucket target can satisfy that ARN
-/// (`reconcile_site_replication_bucket_targets` skips the local peer), so the receiver
-/// silently stops replicating back: the one-directional symptom. Only operator-authored
-/// rules travel between sites; each site owns its own `site-repl-*` rules.
-fn merge_incoming_replication_config(
-    incoming: Option<ReplicationConfiguration>,
-    local: Option<ReplicationConfiguration>,
-) -> Option<ReplicationConfiguration> {
-    let incoming_role = incoming.as_ref().map(|config| config.role.clone()).unwrap_or_default();
-    // Operator rules first, then the local site rules — the same order
-    // `ensure_site_replication_bucket_replication_config_with_runtime` produces, so its
-    // no-op check matches and the bucket metadata is written once per broadcast, not twice.
-    let mut rules: Vec<ReplicationRule> = incoming
-        .into_iter()
-        .flat_map(|config| config.rules)
-        .filter(|rule| !is_site_replication_rule(rule))
-        .collect();
-    rules.extend(
-        local
-            .into_iter()
-            .flat_map(|config| config.rules)
-            .filter(is_site_replication_rule),
-    );
-
-    if rules.is_empty() {
-        return None;
-    }
-
-    for (index, rule) in rules.iter_mut().enumerate() {
-        rule.priority = Some(i32::try_from(index + 1).unwrap_or(i32::MAX));
-    }
-
-    // A site-replication ARN in `role` is the sender's, and `site_replication_target_arns_by_peer`
-    // reads it — carrying it over would pin the receiver's targets to the sender's identity.
-    let role = match replication_target_arn_deployment_id(&incoming_role) {
-        Some(_) => String::new(),
-        None => incoming_role,
-    };
-
-    Some(ReplicationConfiguration { role, rules })
-}
-
 /// Merge a peer's ILM expiry document into the local lifecycle config.
 ///
 /// Mirrors MinIO's `mergeWithCurrentLCConfig` with one hardening: incoming

rustfs/src/admin/storage_api.rs

@@ -443,6 +443,7 @@ pub(crate) mod replication {
     pub(crate) use super::ecstore_bucket::replication::{
         REMOTE_TARGET_CAPABILITY_CONTRACT_VERSION, REMOTE_TARGET_UNSUPPORTED_FIELDS, REMOTE_TARGET_WRITABLE_FIELDS,
         REPLICATION_CAPABILITY_CONTRACT_VERSION, REPLICATION_READ_ONLY_HISTORICAL_FIELDS, REPLICATION_WRITABLE_FIELDS,
+        is_site_replication_rule, merge_incoming_replication_config, replication_target_arn_deployment_id,
     };
     pub(crate) type BucketReplicationResyncStatus = super::ecstore_bucket::replication::BucketReplicationResyncStatus;
     pub(crate) type BucketStats = super::ecstore_bucket::replication::BucketStats;

rustfs/src/app/bucket_usecase.rs

@@ -38,9 +38,9 @@ use super::storage_api::bucket_usecase::bucket::{
     metadata_sys,
     policy_sys::PolicySys,
     replication::{
-        ReplicationTargetValidationError, invalid_replication_config_status_field, replication_target_arns,
-        should_remove_replication_target, unsupported_replication_config_field, validate_replication_config_structure,
-        validate_replication_config_target_arns,
+        ReplicationTargetValidationError, invalid_replication_config_status_field, is_site_replication_rule,
+        merge_incoming_replication_config, replication_target_arns, should_remove_replication_target,
+        unsupported_replication_config_field, validate_replication_config_structure, validate_replication_config_target_arns,
     },
     target::{BucketTargetType, BucketTargets},
     utils::serialize,
@@ -623,11 +623,50 @@ async fn validate_bucket_replication_update(bucket: &str, config: &ReplicationCo
     validate_replication_config_targets(&targets, config)
 }
 
-async fn replication_targets_without_config_targets(
+/// Defense in depth for site-replication-managed buckets (issue #1948): an S3
+/// PutBucketReplication replaces the operator-authored rules but must not wipe
+/// the local `site-repl-*` rules the reconciler owns — until its next pass
+/// (600s period) every peer link on this bucket would be silently dead. The
+/// same merge also drops incoming `site-repl-*` impostor rules, matching the
+/// peer bucket-meta ingestion path. Buckets without site-replication rules
+/// keep the verbatim overwrite semantics.
+fn merge_user_replication_config_update(
+    incoming: ReplicationConfiguration,
+    existing: Option<ReplicationConfiguration>,
+) -> ReplicationConfiguration {
+    let has_site_rules = existing
+        .as_ref()
+        .is_some_and(|config| config.rules.iter().any(is_site_replication_rule));
+    if !has_site_rules {
+        return incoming;
+    }
+    // `existing` holds at least one site-replication rule the merge keeps, so
+    // the merged rule set is non-empty; the fallback only guards the type.
+    merge_incoming_replication_config(Some(incoming.clone()), existing).unwrap_or(incoming)
+}
+
+/// Split of an S3 DeleteBucketReplication on the stored config (issue #1948):
+/// the operator-authored rules are removed, the local `site-repl-*` rules
+/// survive (`None` means nothing survives and the config is deleted), and the
+/// returned ARNs are the ones whose bucket targets may be garbage-collected —
+/// never an ARN a surviving site-replication rule still points at.
+fn split_replication_config_for_user_delete(
+    config: ReplicationConfiguration,
+) -> (Option<ReplicationConfiguration>, HashSet<String>) {
+    let mut removable_arns = replication_target_arns(&config);
+    let remaining = merge_incoming_replication_config(None, Some(config));
+    if let Some(remaining) = remaining.as_ref() {
+        for rule in &remaining.rules {
+            removable_arns.remove(rule.destination.bucket.trim());
+        }
+    }
+    (remaining, removable_arns)
+}
+
+async fn replication_targets_without_arns(
     bucket: &str,
-    config: &ReplicationConfiguration,
+    target_arns: &HashSet<String>,
 ) -> S3Result<Option<(BucketTargets, usize)>> {
-    let target_arns = replication_target_arns(config);
     if target_arns.is_empty() {
         return Ok(None);
     }
@@ -638,7 +677,7 @@ async fn replication_targets_without_config_targets(
         Err(err) => return Err(ApiError::from(err).into()),
     };
 
-    let removed = remove_replication_targets_from_config_targets(&mut targets, &target_arns);
+    let removed = remove_replication_targets_from_config_targets(&mut targets, target_arns);
     if removed == 0 {
         return Ok(None);
     }
@@ -1604,15 +1643,29 @@ impl DefaultBucketUsecase {
             Err(StorageError::ConfigNotFound) => None,
             Err(err) => return Err(ApiError::from(err).into()),
         };
-        let updated_targets = if let Some(config) = replication_config.as_ref() {
-            replication_targets_without_config_targets(&bucket, config).await?
+        let (remaining_config, updated_targets) = if let Some(config) = replication_config.as_ref() {
+            let (remaining, removable_arns) = split_replication_config_for_user_delete(config.clone());
+            let targets = replication_targets_without_arns(&bucket, &removable_arns).await?;
+            (remaining, targets)
         } else {
-            None
+            (None, None)
         };
 
-        delete_bucket_config_for_incarnation(&bucket, BUCKET_REPLICATION_CONFIG, expected_incarnation_id)
-            .await
-            .map_err(ApiError::from)?;
+        match remaining_config {
+            // Site-replication rules and the targets backing them survive the
+            // S3 delete (issue #1948); only the operator-authored rules go.
+            Some(remaining) => {
+                let data = serialize_config(&remaining)?;
+                update_bucket_config_for_incarnation(&bucket, BUCKET_REPLICATION_CONFIG, data, expected_incarnation_id)
+                    .await
+                    .map_err(ApiError::from)?;
+            }
+            None => {
+                delete_bucket_config_for_incarnation(&bucket, BUCKET_REPLICATION_CONFIG, expected_incarnation_id)
+                    .await
+                    .map_err(ApiError::from)?;
+            }
+        }
         if let Some((targets, removed)) = updated_targets
             && let Err(err) =
                 write_replication_targets_after_config_delete(&bucket, &targets, removed, expected_incarnation_id).await
@@ -2485,6 +2538,12 @@ impl DefaultBucketUsecase {
 
         let targets_guard = lock_bucket_targets_metadata(&bucket).await;
         validate_bucket_replication_update(&bucket, &replication_configuration).await?;
+        let existing_config = match metadata_sys::get_replication_config(&bucket).await {
+            Ok((config, _)) => Some(config),
+            Err(StorageError::ConfigNotFound) => None,
+            Err(err) => return Err(ApiError::from(err).into()),
+        };
+        let replication_configuration = merge_user_replication_config_update(replication_configuration, existing_config);
         let data = serialize_config(&replication_configuration)?;
         update_bucket_config_for_incarnation(&bucket, BUCKET_REPLICATION_CONFIG, data, expected_incarnation_id)
             .await
@@ -3114,6 +3173,127 @@ mod tests {
         assert!(arns.contains(destination));
     }
 
+    fn replication_rule_with_id(arn: &str, id: &str, priority: i32) -> ReplicationRule {
+        let mut rule = replication_rule_for_target(arn);
+        rule.id = Some(id.to_string());
+        rule.priority = Some(priority);
+        rule
+    }
+
+    #[test]
+    fn put_replication_merge_preserves_site_replication_rules() {
+        let existing = ReplicationConfiguration {
+            role: String::new(),
+            rules: vec![
+                replication_rule_with_id("arn:rustfs:replication::peer-dep:bucket", "site-repl-peer-dep", 1),
+                replication_rule_with_id("arn:rustfs:replication:us-east-1:old:bucket", "old-user-rule", 2),
+            ],
+        };
+        let incoming = ReplicationConfiguration {
+            role: String::new(),
+            rules: vec![
+                replication_rule_with_id("arn:rustfs:replication:us-east-1:new:bucket", "new-user-rule", 1),
+                replication_rule_with_id("arn:rustfs:replication::forged-dep:bucket", "site-repl-forged", 2),
+            ],
+        };
+
+        let merged = merge_user_replication_config_update(incoming, Some(existing));
+
+        let ids: Vec<_> = merged
+            .rules
+            .iter()
+            .map(|rule| rule.id.as_deref().unwrap_or_default())
+            .collect();
+        assert_eq!(
+            ids,
+            vec!["new-user-rule", "site-repl-peer-dep"],
+            "user rules replaced, local site-replication rule preserved, forged incoming site-repl rule dropped"
+        );
+    }
+
+    #[test]
+    fn put_replication_merge_returns_incoming_verbatim_without_site_rules() {
+        let existing = ReplicationConfiguration {
+            role: String::new(),
+            rules: vec![replication_rule_with_id(
+                "arn:rustfs:replication:us-east-1:old:bucket",
+                "old-user-rule",
+                7,
+            )],
+        };
+        let incoming = ReplicationConfiguration {
+            role: String::new(),
+            rules: vec![replication_rule_with_id(
+                "arn:rustfs:replication:us-east-1:new:bucket",
+                "new-user-rule",
+                5,
+            )],
+        };
+
+        let merged = merge_user_replication_config_update(incoming.clone(), Some(existing));
+
+        assert_eq!(merged.role, incoming.role);
+        assert_eq!(merged.rules, incoming.rules, "non-SR buckets keep the verbatim overwrite semantics");
+    }
+
+    #[test]
+    fn delete_replication_split_keeps_site_rules_and_their_targets() {
+        let sr_arn = "arn:rustfs:replication::peer-dep:bucket";
+        let user_arn = "arn:rustfs:replication:us-east-1:user:bucket";
+        let config = ReplicationConfiguration {
+            role: String::new(),
+            rules: vec![
+                replication_rule_with_id(user_arn, "user-rule", 1),
+                replication_rule_with_id(sr_arn, "site-repl-peer-dep", 2),
+            ],
+        };
+
+        let (remaining, removable) = split_replication_config_for_user_delete(config);
+
+        let remaining = remaining.expect("site-replication rules must survive a user delete");
+        let ids: Vec<_> = remaining
+            .rules
+            .iter()
+            .map(|rule| rule.id.as_deref().unwrap_or_default())
+            .collect();
+        assert_eq!(ids, vec!["site-repl-peer-dep"]);
+        assert_eq!(removable, HashSet::from([user_arn.to_string()]));
+    }
+
+    #[test]
+    fn delete_replication_split_protects_targets_shared_with_site_rules() {
+        let sr_arn = "arn:rustfs:replication::peer-dep:bucket";
+        let config = ReplicationConfiguration {
+            role: String::new(),
+            rules: vec![
+                replication_rule_with_id(sr_arn, "user-rule-on-sr-target", 1),
+                replication_rule_with_id(sr_arn, "site-repl-peer-dep", 2),
+            ],
+        };
+
+        let (remaining, removable) = split_replication_config_for_user_delete(config);
+
+        assert!(remaining.is_some());
+        assert!(
+            removable.is_empty(),
+            "a target still referenced by a surviving site-replication rule must not be removed"
+        );
+    }
+
+    #[test]
+    fn delete_replication_split_removes_everything_without_site_rules() {
+        let user_arn = "arn:rustfs:replication:us-east-1:user:bucket";
+        let config = ReplicationConfiguration {
+            role: String::new(),
+            rules: vec![replication_rule_with_id(user_arn, "user-rule", 1)],
+        };
+
+        let (remaining, removable) = split_replication_config_for_user_delete(config);
+
+        assert!(remaining.is_none(), "without site-replication rules the whole config is deleted");
+        assert_eq!(removable, HashSet::from([user_arn.to_string()]));
+    }
+
     fn replication_targets_with_arn(arns: &[&str]) -> BucketTargets {
         BucketTargets {
             targets: arns

rustfs/src/app/storage_api.rs

@@ -614,6 +614,8 @@ pub(crate) mod bucket {
 
         use crate::storage::storage_api::ecstore_bucket::replication as replication_contracts;
 
+        pub(crate) use replication_contracts::{is_site_replication_rule, merge_incoming_replication_config};
+
         type ReplicationObjectBridge = crate::storage::storage_api::ecstore_bucket::replication::ReplicationObjectBridge;
         pub(crate) type DeleteReplicationConfigSnapshot =
             crate::storage::storage_api::ecstore_bucket::replication::DeleteReplicationConfigSnapshot;

rustfs/src/storage/ecfs.rs

@@ -63,6 +63,54 @@ use crate::app::storage_api::object_usecase::bucket::replication::{
 };
 use crate::storage::storage_api::ecfs_consumer::StorageObjectOptions as ObjectOptions;
 
+#[cfg(test)]
+static SITE_REPLICATION_GATE_TEST_OVERRIDE: std::sync::atomic::AtomicU8 = std::sync::atomic::AtomicU8::new(0);
+#[cfg(test)]
+const SITE_REPLICATION_GATE_FORCE_DISABLED: u8 = 1;
+#[cfg(test)]
+const SITE_REPLICATION_GATE_FORCE_ENABLED: u8 = 2;
+
+async fn site_replication_gate_enabled() -> S3Result<bool> {
+    #[cfg(test)]
+    match SITE_REPLICATION_GATE_TEST_OVERRIDE.load(std::sync::atomic::Ordering::SeqCst) {
+        SITE_REPLICATION_GATE_FORCE_DISABLED => return Ok(false),
+        SITE_REPLICATION_GATE_FORCE_ENABLED => return Ok(true),
+        _ => {}
+    }
+    crate::admin::handlers::site_replication::site_replication_enabled().await
+}
+
+/// MinIO `ErrReplicationDenyEditError`.
+fn replication_deny_edit_error() -> S3Error {
+    let mut err = S3Error::with_message(
+        S3ErrorCode::Custom("XMinioReplicationDenyEdit".into()),
+        "Sub-User is not allowed to edit Replication configuration",
+    );
+    err.set_status_code(StatusCode::BAD_REQUEST);
+    err
+}
+
+/// Site-replication gate for S3 replication-config edits (issue #1948).
+///
+/// On a site-replication deployment the bucket's replication config carries
+/// the operator-managed `site-repl-*` rules that keep every peer in sync, and
+/// a successful edit is broadcast to all peers — so a user holding only
+/// bucket-scoped `s3:PutReplicationConfiguration` could rewrite or erase
+/// replication net-wide. MinIO parity (`ErrReplicationDenyEditError`): only
+/// owner credentials (root or root-parented) may edit. Runs after the policy
+/// authorization in the access layer and only on the external S3 path — the
+/// reconciler and peer bucket-meta ingestion never route through these
+/// handlers.
+async fn deny_replication_config_edit_for_non_owner<T>(req: &S3Request<T>) -> S3Result<()> {
+    if crate::storage::access::req_info_ref(req)?.is_owner {
+        return Ok(());
+    }
+    if site_replication_gate_enabled().await? {
+        return Err(replication_deny_edit_error());
+    }
+    Ok(())
+}
+
 #[derive(Debug, Clone)]
 pub struct FS {
     /// This server's late-bound application-context slot (backlog#1052 S2).
@@ -500,6 +548,7 @@ impl S3 for FS {
         &self,
         req: S3Request<DeleteBucketReplicationInput>,
     ) -> S3Result<S3Response<DeleteBucketReplicationOutput>> {
+        deny_replication_config_edit_for_non_owner(&req).await?;
         let usecase = s3_api::bucket_usecase_for(self);
         usecase.execute_delete_bucket_replication(req).await
     }
@@ -1353,6 +1402,7 @@ impl S3 for FS {
         &self,
         req: S3Request<PutBucketReplicationInput>,
     ) -> S3Result<S3Response<PutBucketReplicationOutput>> {
+        deny_replication_config_edit_for_non_owner(&req).await?;
         let usecase = s3_api::bucket_usecase_for(self);
         usecase.execute_put_bucket_replication(req).await
     }
@@ -1919,3 +1969,103 @@ impl S3 for FS {
         Box::pin(usecase.execute_upload_part_copy(req)).await
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::{
+        FS, SITE_REPLICATION_GATE_FORCE_DISABLED, SITE_REPLICATION_GATE_FORCE_ENABLED, SITE_REPLICATION_GATE_TEST_OVERRIDE,
+    };
+    use crate::storage::access::ReqInfo;
+    use http::Method;
+    use http::StatusCode;
+    use s3s::dto::{DeleteBucketReplicationInput, PutBucketReplicationInput, ReplicationConfiguration};
+    use s3s::{S3, S3Error, S3ErrorCode, S3Request};
+    use std::sync::atomic::Ordering;
+
+    fn replication_config_edit_request<T>(input: T, is_owner: bool) -> S3Request<T> {
+        let mut req = S3Request {
+            input,
+            method: Method::PUT,
+            uri: http::Uri::from_static("/"),
+            headers: http::HeaderMap::new(),
+            extensions: http::Extensions::new(),
+            credentials: None,
+            region: None,
+            service: None,
+            trailing_headers: None,
+        };
+        req.extensions.insert(ReqInfo {
+            is_owner,
+            ..Default::default()
+        });
+        req
+    }
+
+    fn put_bucket_replication_input() -> PutBucketReplicationInput {
+        PutBucketReplicationInput {
+            bucket: "test-bucket".to_string(),
+            checksum_algorithm: None,
+            content_md5: None,
+            expected_bucket_owner: None,
+            replication_configuration: ReplicationConfiguration {
+                role: String::new(),
+                rules: Vec::new(),
+            },
+            token: None,
+        }
+    }
+
+    fn delete_bucket_replication_input() -> DeleteBucketReplicationInput {
+        DeleteBucketReplicationInput {
+            bucket: "test-bucket".to_string(),
+            expected_bucket_owner: None,
+        }
+    }
+
+    fn assert_replication_deny_edit(err: &S3Error) {
+        match err.code() {
+            S3ErrorCode::Custom(code) => assert_eq!(code, "XMinioReplicationDenyEdit"),
+            other => panic!("expected XMinioReplicationDenyEdit, got {other:?}"),
+        }
+        assert_eq!(err.status_code(), Some(StatusCode::BAD_REQUEST));
+    }
+
+    /// Single test on purpose: the branches share the process-wide gate
+    /// override, and parallel tests would race it.
+    #[tokio::test]
+    async fn replication_config_edit_gate_denies_only_non_owner_under_site_replication() {
+        let fs = FS::new();
+        SITE_REPLICATION_GATE_TEST_OVERRIDE.store(SITE_REPLICATION_GATE_FORCE_ENABLED, Ordering::SeqCst);
+
+        // Non-owner PUT/DELETE through the real S3 handlers: denied by the
+        // gate before the usecase (and thus the store) is ever touched.
+        let err = fs
+            .put_bucket_replication(replication_config_edit_request(put_bucket_replication_input(), false))
+            .await
+            .expect_err("non-owner PutBucketReplication must be denied while site replication is enabled");
+        assert_replication_deny_edit(&err);
+        let err = fs
+            .delete_bucket_replication(replication_config_edit_request(delete_bucket_replication_input(), false))
+            .await
+            .expect_err("non-owner DeleteBucketReplication must be denied while site replication is enabled");
+        assert_replication_deny_edit(&err);
+
+        // Owner passes the gate (the usecase's empty-rules structure error
+        // proves the request reached the usecase instead of the deny path).
+        let err = fs
+            .put_bucket_replication(replication_config_edit_request(put_bucket_replication_input(), true))
+            .await
+            .expect_err("owner request should pass the gate and fail later on config validation");
+        assert_eq!(err.code(), &S3ErrorCode::InvalidRequest);
+
+        // Without site replication the policy check alone still governs the edit.
+        SITE_REPLICATION_GATE_TEST_OVERRIDE.store(SITE_REPLICATION_GATE_FORCE_DISABLED, Ordering::SeqCst);
+        let err = fs
+            .put_bucket_replication(replication_config_edit_request(put_bucket_replication_input(), false))
+            .await
+            .expect_err("non-owner request should pass the gate and fail later on config validation");
+        assert_eq!(err.code(), &S3ErrorCode::InvalidRequest);
+
+        SITE_REPLICATION_GATE_TEST_OVERRIDE.store(0, Ordering::SeqCst);
+    }
+}