diff --git a/CHANGELOG.md b/CHANGELOG.md
index 97e03a49..22817633 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -24,6 +24,7 @@ and this project adheres to
 - 🐛(frontend) keep the sending resolution picked while the camera is off #1667
 - 🐛(frontend) restore automatic lower-hand on speaking
 - 🐛(frontend) center Avatar initials with a font-aware cap-height ratio
+- 🔒️(backend) reject inactive users in resource server backend
 
 ## [1.30.0] - 2026-09-01
 
diff --git a/src/backend/core/external_api/authentication.py b/src/backend/core/external_api/authentication.py
index 496624f3..445eb02f 100644
--- a/src/backend/core/external_api/authentication.py
+++ b/src/backend/core/external_api/authentication.py
@@ -286,6 +286,10 @@ class ResourceServerBackend(LaSuiteBackend):
         if user is None and settings.OIDC_CREATE_USER:
             user = self.create_user(sub)
 
+        if user is not None and not user.is_active:
+            logger.warning("Inactive user attempted authentication: %s", user.pk)
+            raise SuspiciousOperation("User account is disabled.")
+
         return user
 
     def create_user(self, sub):
diff --git a/src/backend/core/tests/test_external_api_authentication.py b/src/backend/core/tests/test_external_api_authentication.py
new file mode 100644
index 00000000..d3191f10
--- /dev/null
+++ b/src/backend/core/tests/test_external_api_authentication.py
@@ -0,0 +1,96 @@
+"""Tests for the external API ResourceServerBackend."""
+
+from django.core.exceptions import SuspiciousOperation
+
+import pytest
+import responses
+from rest_framework.test import APIClient
+
+from core.external_api.authentication import ResourceServerBackend
+from core.factories import UserFactory
+from core.models import User
+
+pytestmark = pytest.mark.django_db
+
+
+def _payload(sub):
+    return {"sub": sub, "active": True, "scope": "lasuite_meet", "client_id": "app"}
+
+
+def test_resource_server_backend_get_or_create_user_active():
+    """An existing active user matching the sub should be returned."""
+
+    user = UserFactory()
+
+    result = ResourceServerBackend().get_or_create_user(
+        access_token="token", id_token=None, payload=_payload(user.sub)
+    )
+
+    assert result == user
+
+
+def test_resource_server_backend_get_or_create_user_inactive():
+    """An inactive user should be rejected even with a valid token."""
+
+    user = UserFactory(is_active=False)
+
+    with pytest.raises(SuspiciousOperation, match="User account is disabled."):
+        ResourceServerBackend().get_or_create_user(
+            access_token="token", id_token=None, payload=_payload(user.sub)
+        )
+
+
+def test_resource_server_backend_get_or_create_user_creates(settings):
+    """An unknown sub should create an active user when OIDC_CREATE_USER is set."""
+
+    settings.OIDC_CREATE_USER = True
+
+    result = ResourceServerBackend().get_or_create_user(
+        access_token="token", id_token=None, payload=_payload("new-sub")
+    )
+
+    assert result.sub == "new-sub"
+    assert result.is_active is True
+    assert User.objects.filter(sub="new-sub").exists()
+
+
+def test_resource_server_backend_get_or_create_user_no_creation(settings):
+    """An unknown sub should return None when OIDC_CREATE_USER is unset."""
+
+    settings.OIDC_CREATE_USER = False
+
+    result = ResourceServerBackend().get_or_create_user(
+        access_token="token", id_token=None, payload=_payload("new-sub")
+    )
+
+    assert result is None
+    assert not User.objects.filter(sub="new-sub").exists()
+
+
+@responses.activate
+def test_api_rooms_list_resource_server_inactive_user(settings):
+    """End to end: a valid introspected token for an inactive user should get 401."""
+
+    settings.OIDC_OP_INTROSPECTION_ENDPOINT = "https://oidc.example.com/introspect"
+    settings.OIDC_OP_URL = "https://oidc.example.com"
+
+    user = UserFactory(is_active=False)
+
+    responses.add(
+        responses.POST,
+        "https://oidc.example.com/introspect",
+        json={
+            "iss": "https://oidc.example.com",
+            "active": True,
+            "sub": user.sub,
+            "scope": "lasuite_meet",
+            "client_id": "app",
+        },
+    )
+
+    client = APIClient()
+    client.credentials(HTTP_AUTHORIZATION="Bearer rs-token")
+    response = client.get("/external-api/v1.0/rooms/")
+
+    assert response.status_code == 401
+    assert "login failed" in str(response.data).lower()