diff --git a/CHANGELOG.md b/CHANGELOG.md
index 86c286a5e..53dd6ff37 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -24,6 +24,7 @@ and this project adheres to
 - 🐛(backend) ignore CSPs for API docs in development
 - 🐛(frontend) export images embedded with a relative url #2573
 - 🐛(y-provider) fix sentry init #2579
+- 🐛(backend) handle object storage metadata keys case-insensitively #2576
 - 🐛(keycloak) fix database env variables in the self-hosting example #2572
 - 🐛(helm) show the database error while jobs wait for it to be ready #2578
 
diff --git a/src/backend/core/api/viewsets.py b/src/backend/core/api/viewsets.py
index 5d9991bcb..e63fb726d 100644
--- a/src/backend/core/api/viewsets.py
+++ b/src/backend/core/api/viewsets.py
@@ -71,6 +71,7 @@ from core.services.search_indexers import (
 from core.tasks.access import reset_service_connections_in_cascade
 from core.tasks.mail import send_ask_for_access_mail
 from core.utils.analytics import PosthogEventName, posthog_capture
+from core.utils.dicts import lowercase_keys
 from core.utils.paths import filter_descendants
 from core.utils.s3_response_stream import content_stream
 from core.utils.treebeard import create_tree_node_with_retry
@@ -1884,7 +1885,7 @@ class DocumentViewSet(
         extra_args = {
             "Metadata": {
                 "owner": str(request.user.id),
-                "status": enums.DocumentAttachmentStatus.PROCESSING,
+                "status": enums.DocumentAttachmentStatus.PROCESSING.value,
             },
             "ContentType": serializer.validated_data["content_type"],
         }
@@ -2034,7 +2035,7 @@ class DocumentViewSet(
             head_resp = s3_client.head_object(Bucket=bucket_name, Key=key)
         except ClientError as err:
             raise drf.exceptions.PermissionDenied() from err
-        metadata = head_resp.get("Metadata", {})
+        metadata = lowercase_keys(head_resp.get("Metadata", {}))
         # In order to be compatible with existing upload without `status` metadata,
         # we consider them as ready.
         if (
@@ -2238,7 +2239,7 @@ class DocumentViewSet(
                 {"detail": "Media not found"},
                 status=drf.status.HTTP_404_NOT_FOUND,
             )
-        metadata = head_resp.get("Metadata", {})
+        metadata = lowercase_keys(head_resp.get("Metadata", {}))
 
         body = {
             "status": metadata.get("status", enums.DocumentAttachmentStatus.PROCESSING),
diff --git a/src/backend/core/malware_detection.py b/src/backend/core/malware_detection.py
index 9b1ef3a72..e126fed1f 100644
--- a/src/backend/core/malware_detection.py
+++ b/src/backend/core/malware_detection.py
@@ -8,6 +8,7 @@ from lasuite.malware_detection.enums import ReportStatus
 
 from core.enums import DocumentAttachmentStatus
 from core.models import Document
+from core.utils.dicts import lowercase_keys
 
 logger = logging.getLogger(__name__)
 security_logger = logging.getLogger("docs.security")
@@ -22,8 +23,8 @@ def malware_detection_callback(file_path, status, error_info, **kwargs):
         s3_client = default_storage.connection.meta.client
         bucket_name = default_storage.bucket_name
         head_resp = s3_client.head_object(Bucket=bucket_name, Key=file_path)
-        metadata = head_resp.get("Metadata", {})
-        metadata.update({"status": DocumentAttachmentStatus.READY})
+        metadata = lowercase_keys(head_resp.get("Metadata", {}))
+        metadata.update({"status": DocumentAttachmentStatus.READY.value})
         # Update status in metadata
         s3_client.copy_object(
             Bucket=bucket_name,
diff --git a/src/backend/core/management/commands/update_files_content_type_metadata.py b/src/backend/core/management/commands/update_files_content_type_metadata.py
index bb2e5253a..2373dfb16 100644
--- a/src/backend/core/management/commands/update_files_content_type_metadata.py
+++ b/src/backend/core/management/commands/update_files_content_type_metadata.py
@@ -6,6 +6,7 @@ from django.core.management.base import BaseCommand
 import magic
 
 from core.models import Document
+from core.utils.dicts import lowercase_keys
 
 # pylint: disable=too-many-locals, broad-exception-caught
 
@@ -74,7 +75,7 @@ class Command(BaseCommand):
                             CopySource={"Bucket": bucket_name, "Key": key},
                             Key=key,
                             ContentType=magic_mime_type,
-                            Metadata=head_resp.get("Metadata", {}),
+                            Metadata=lowercase_keys(head_resp.get("Metadata", {})),
                             MetadataDirective="REPLACE",
                         )
                         total_updated += 1
diff --git a/src/backend/core/tests/documents/test_api_documents_media_auth.py b/src/backend/core/tests/documents/test_api_documents_media_auth.py
index 35ea8b2b6..40514dad2 100644
--- a/src/backend/core/tests/documents/test_api_documents_media_auth.py
+++ b/src/backend/core/tests/documents/test_api_documents_media_auth.py
@@ -3,6 +3,7 @@ Test media-auth authorization API endpoint in docs core app.
 """
 
 from io import BytesIO
+from unittest.mock import patch
 from urllib.parse import urlparse
 from uuid import uuid4
 
@@ -369,6 +370,34 @@ def test_api_documents_media_auth_not_ready_status():
     assert response.status_code == 403
 
 
+def test_api_documents_media_auth_uppercase_status_metadata():
+    """
+    Object storage metadata keys are case insensitive, and some S3 implementations give them
+    back capitalized. A ready attachment should still be served in that case.
+    """
+    document_id = uuid4()
+    filename = f"{uuid4()!s}.jpg"
+    key = f"{document_id!s}/attachments/{filename:s}"
+
+    factories.DocumentFactory(id=document_id, link_reach="public", attachments=[key])
+
+    head_resp = {
+        "ContentType": "text/plain",
+        "Metadata": {"Status": DocumentAttachmentStatus.READY.value},
+    }
+
+    original_url = f"http://localhost/media/{key:s}"
+    with patch.object(
+        default_storage.connection.meta.client, "head_object", return_value=head_resp
+    ):
+        response = APIClient().get(
+            "/api/v1.0/documents/media-auth/", HTTP_X_ORIGINAL_URL=original_url
+        )
+
+    assert response.status_code == 200
+    assert "AWS4-HMAC-SHA256 Credential=" in response["Authorization"]
+
+
 def test_api_documents_media_auth_missing_status_metadata(settings):
     """Attachments without status metadata should be considered as ready"""
     document_id = uuid4()
diff --git a/src/backend/core/tests/documents/test_api_documents_media_check.py b/src/backend/core/tests/documents/test_api_documents_media_check.py
index 81cec061e..b5a472c97 100644
--- a/src/backend/core/tests/documents/test_api_documents_media_check.py
+++ b/src/backend/core/tests/documents/test_api_documents_media_check.py
@@ -1,6 +1,7 @@
 """Test the "media_check" endpoint."""
 
 from io import BytesIO
+from unittest.mock import patch
 from uuid import uuid4
 
 from django.core.files.storage import default_storage
@@ -116,6 +117,39 @@ def test_api_documents_media_check_anonymous_public_document_ready():
     }
 
 
+def test_api_documents_media_check_uppercase_status_metadata():
+    """
+    Object storage metadata keys are case insensitive, and some S3 implementations give them
+    back capitalized. The "media_check" endpoint should still report the attachment as ready.
+    """
+    document = factories.DocumentFactory(link_reach="public")
+
+    filename = f"{uuid4()!s}.jpg"
+    key = f"{document.id!s}/attachments/{filename:s}"
+    document.attachments = [key]
+    document.save(update_fields=["attachments"])
+
+    head_resp = {
+        "ContentType": "text/plain",
+        "Metadata": {"Status": DocumentAttachmentStatus.READY.value},
+    }
+
+    client = APIClient()
+
+    with patch.object(
+        default_storage.connection.meta.client, "head_object", return_value=head_resp
+    ):
+        response = client.get(
+            f"/api/v1.0/documents/{document.id!s}/media-check/", {"key": key}
+        )
+
+    assert response.status_code == 200
+    assert response.json() == {
+        "status": DocumentAttachmentStatus.READY,
+        "file": f"/media/{key:s}",
+    }
+
+
 @pytest.mark.parametrize("link_reach", ["restricted", "authenticated"])
 def test_api_documents_media_check_anonymous_non_public_document(link_reach):
     """
diff --git a/src/backend/core/tests/test_malware_detection.py b/src/backend/core/tests/test_malware_detection.py
index 57da7643d..5fb017ad6 100644
--- a/src/backend/core/tests/test_malware_detection.py
+++ b/src/backend/core/tests/test_malware_detection.py
@@ -1,6 +1,7 @@
 """Test malware detection callback."""
 
 import random
+from unittest.mock import patch
 
 from django.core.files.base import ContentFile
 from django.core.files.storage import default_storage
@@ -56,6 +57,41 @@ def test_malware_detection_callback_safe_status(safe_file):
     assert metadata["status"] == DocumentAttachmentStatus.READY
 
 
+def test_malware_detection_callback_safe_status_uppercase_metadata(safe_file):
+    """
+    Object storage metadata keys are case insensitive, and some S3 implementations give them
+    back capitalized. The callback should update the existing "status" entry instead of adding
+    a second one, which would end up as two "x-amz-meta-status" headers on the copy request.
+    """
+    document = DocumentFactory(attachments=[safe_file])
+
+    s3_client = default_storage.connection.meta.client
+    head_resp = {
+        "ContentType": "text/plain",
+        "Metadata": {
+            "Owner": str(document.id),
+            "Status": DocumentAttachmentStatus.PROCESSING.value,
+        },
+    }
+
+    with (
+        patch.object(s3_client, "head_object", return_value=head_resp),
+        patch.object(s3_client, "copy_object") as mock_copy_object,
+    ):
+        malware_detection_callback(
+            safe_file,
+            ReportStatus.SAFE,
+            error_info={},
+            document_id=document.id,
+        )
+
+    metadata = mock_copy_object.call_args.kwargs["Metadata"]
+    assert metadata == {
+        "owner": str(document.id),
+        "status": DocumentAttachmentStatus.READY.value,
+    }
+
+
 def test_malware_detection_callback_unsafe_status(unsafe_file):
     """Test malware detection callback with unsafe status."""
 
diff --git a/src/backend/core/tests/test_utils.py b/src/backend/core/tests/test_utils.py
index 33c7c643e..99c2f4d2b 100644
--- a/src/backend/core/tests/test_utils.py
+++ b/src/backend/core/tests/test_utils.py
@@ -9,7 +9,7 @@ import pycrdt
 import pytest
 
 from core import factories
-from core.utils.dicts import get_value_by_pattern
+from core.utils.dicts import get_value_by_pattern, lowercase_keys
 from core.utils.paths import get_ancestor_to_descendants_map
 from core.utils.users import (
     get_users_sharing_documents_with_cache_key,
@@ -251,3 +251,35 @@ def test_utils_get_value_by_pattern_no_match():
     result = get_value_by_pattern(data, r"^title\.")
 
     assert result == []
+
+
+def test_utils_lowercase_keys_empty():
+    """Test that an empty dictionary is returned untouched."""
+    assert lowercase_keys({}) == {}
+
+
+def test_utils_lowercase_keys_mixed_case():
+    """Test that keys are lowercased while values are left untouched."""
+    data = {"Owner": "42", "STATUS": "Ready", "is_unsafe": "true"}
+
+    assert lowercase_keys(data) == {
+        "owner": "42",
+        "status": "Ready",
+        "is_unsafe": "true",
+    }
+
+
+def test_utils_lowercase_keys_collision():
+    """Test that keys differing only by their case are collapsed into a single one."""
+    data = {"Status": "processing", "status": "ready"}
+    result = lowercase_keys(data)
+
+    assert result == {"status": "ready"}
+
+
+def test_utils_lowercase_keys_does_not_mutate_source():
+    """Test that the source dictionary is left untouched."""
+    data = {"Status": "processing"}
+    lowercase_keys(data)
+
+    assert data == {"Status": "processing"}
diff --git a/src/backend/core/utils/dicts.py b/src/backend/core/utils/dicts.py
index 8cc7aa4bc..faf8b13fb 100644
--- a/src/backend/core/utils/dicts.py
+++ b/src/backend/core/utils/dicts.py
@@ -22,3 +22,25 @@ def get_value_by_pattern(data, pattern):
     """
     regex = re.compile(pattern)
     return [value for key, value in data.items() if regex.match(key)]
+
+
+def lowercase_keys(data):
+    """
+    Get a copy of a dictionary with all its keys lowercased.
+
+    Useful for object storage metadata: keys are case insensitive per the S3 specification,
+    but implementations don't agree on the case they give back, so reading or updating a
+    metadata entry by its lowercase name is only reliable after this normalization.
+
+    Args:
+        data (dict): Source dictionary
+
+    Returns:
+        dict: New dictionary with lowercased keys. When several keys only differ by their
+            case, the last one encountered wins.
+
+    Example:
+        >>> lowercase_keys({"Owner": "42", "Status": "ready"})
+        {"owner": "42", "status": "ready"}
+    """
+    return {key.lower(): value for key, value in data.items()}