diff --git a/weed/s3api/auth_credentials.go b/weed/s3api/auth_credentials.go
index 1e93bb632..48a5ccbc0 100644
--- a/weed/s3api/auth_credentials.go
+++ b/weed/s3api/auth_credentials.go
@@ -169,20 +169,17 @@ func NewIdentityAccessManagementWithStore(option *S3ApiServerOption, explicitSto
 		if err := iam.loadS3ApiConfigurationFromFile(option.Config); err != nil {
 			glog.Fatalf("fail to load config file %s: %v", option.Config, err)
 		}
-		iam.useStaticConfig = true
 
 		// Track identity names from static config to protect them from dynamic updates
+		// Must be done under lock to avoid race conditions
 		iam.m.Lock()
+		iam.useStaticConfig = true
 		iam.staticIdentityNames = make(map[string]bool)
 		for _, identity := range iam.identities {
 			iam.staticIdentityNames[identity.Name] = true
 		}
-		iam.m.Unlock()
-
-		// Check if any identities were actually loaded from the config file
-		iam.m.RLock()
 		configLoaded = len(iam.identities) > 0
-		iam.m.RUnlock()
+		iam.m.Unlock()
 	} else {
 		glog.V(3).Infof("no static config file specified... loading config from credential manager")
 		if err := iam.loadS3ApiConfigurationFromFiler(option); err != nil {
@@ -544,17 +541,17 @@ func (iam *IdentityAccessManagement) mergeS3ApiConfiguration(config *iam_pb.S3Ap
 		}
 
 		// Update or add the identity
-		if existingIdx := -1; existingIdx >= 0 {
-			// Find and replace existing dynamic identity
-			for i, existing := range identities {
-				if existing.Name == ident.Name {
-					existingIdx = i
-					break
-				}
-			}
-			if existingIdx >= 0 {
-				identities[existingIdx] = t
+		existingIdx := -1
+		for i, existing := range identities {
+			if existing.Name == ident.Name {
+				existingIdx = i
+				break
 			}
+		}
+
+		if existingIdx >= 0 {
+			// Replace existing dynamic identity
+			identities[existingIdx] = t
 		} else {
 			// Add new dynamic identity
 			identities = append(identities, t)
@@ -1226,6 +1223,12 @@ func determineIAMAuthPath(sessionToken, principal, principalArn string) iamAuthP
 // VerifyActionPermission checks if the identity is allowed to perform the action on the resource.
 // It handles both traditional identities (via Actions) and IAM/STS identities (via Policy).
 func (iam *IdentityAccessManagement) VerifyActionPermission(r *http.Request, identity *Identity, action Action, bucket, object string) s3err.ErrorCode {
+	// Fail closed if identity is nil
+	if identity == nil {
+		glog.V(3).Infof("VerifyActionPermission called with nil identity for action %s on %s/%s", action, bucket, object)
+		return s3err.ErrAccessDenied
+	}
+
 	// Traditional identities (with Actions from -s3.config) use legacy auth,
 	// JWT/STS identities (no Actions) use IAM authorization
 	if len(identity.Actions) > 0 {
diff --git a/weed/s3api/auth_credentials_subscribe.go b/weed/s3api/auth_credentials_subscribe.go
index e2d54e307..06d771cc4 100644
--- a/weed/s3api/auth_credentials_subscribe.go
+++ b/weed/s3api/auth_credentials_subscribe.go
@@ -59,6 +59,10 @@ func (s3a *S3ApiServer) onIamConfigChange(dir string, oldEntry *filer_pb.Entry,
 	if dir != filer.IamConfigDirectory {
 		return nil
 	}
+	if s3a.iam != nil && s3a.iam.IsStaticConfig() {
+		glog.V(1).Infof("Skipping IAM config update for static configuration")
+		return nil
+	}
 
 	// Handle deletion: reset to empty config
 	if newEntry == nil && oldEntry != nil && oldEntry.Name == filer.IamIdentityFile {
diff --git a/weed/s3api/auth_signature_v4.go b/weed/s3api/auth_signature_v4.go
index c8127c638..7ebdefd1c 100644
--- a/weed/s3api/auth_signature_v4.go
+++ b/weed/s3api/auth_signature_v4.go
@@ -337,8 +337,16 @@ func (iam *IdentityAccessManagement) validateSTSSessionToken(r *http.Request, se
 
 	// Verify that the access key in the request matches the one in the session token
 	if sessionInfo.Credentials.AccessKeyId != accessKey {
+		// Mask access keys to avoid exposing credentials in logs
+		truncateKey := func(k string) string {
+			const mask = "***"
+			if len(k) > 4 {
+				return k[:4] + mask
+			}
+			return mask
+		}
 		glog.V(2).Infof("Access key mismatch: request has %s, session token has %s",
-			accessKey, sessionInfo.Credentials.AccessKeyId)
+			truncateKey(accessKey), truncateKey(sessionInfo.Credentials.AccessKeyId))
 		return nil, nil, s3err.ErrInvalidAccessKeyID
 	}
 
diff --git a/weed/s3api/auth_signature_v4_sts_test.go b/weed/s3api/auth_signature_v4_sts_test.go
index 1d9fd5d41..077d67770 100644
--- a/weed/s3api/auth_signature_v4_sts_test.go
+++ b/weed/s3api/auth_signature_v4_sts_test.go
@@ -16,9 +16,11 @@ import (
 // MockIAMIntegration is a mock implementation of IAM integration for testing
 type MockIAMIntegration struct {
 	authorizeFunc func(ctx context.Context, identity *IAMIdentity, action Action, bucket, object string, r *http.Request) s3err.ErrorCode
+	authCalled    bool
 }
 
 func (m *MockIAMIntegration) AuthorizeAction(ctx context.Context, identity *IAMIdentity, action Action, bucket, object string, r *http.Request) s3err.ErrorCode {
+	m.authCalled = true
 	if m.authorizeFunc != nil {
 		return m.authorizeFunc(ctx, identity, action, bucket, object, r)
 	}
@@ -169,7 +171,7 @@ func TestVerifyV4SignatureWithSTSIdentity(t *testing.T) {
 			if len(tt.identity.Actions) == 0 && tt.shouldCheckPermissions {
 				if tt.iamIntegration != nil {
 					// When IAM integration exists, it should have been called
-					// The result depends on what the mock returns
+					assert.True(t, tt.iamIntegration.authCalled, "IAM integration should have been called for STS identity")
 				} else {
 					assert.Equal(t, s3err.ErrAccessDenied, errCode, "STS identity should be denied without IAM integration")
 				}