diff --git a/src/openenv/validation/local.py b/src/openenv/validation/local.py
index 94526424c..1088cf46b 100644
--- a/src/openenv/validation/local.py
+++ b/src/openenv/validation/local.py
@@ -96,6 +96,24 @@ def _runtime_environment(
     return process_env
 
 
+def _subject_process_kwargs() -> dict[str, Any]:
+    """Return POSIX identity controls supplied by a trusted isolated runner."""
+    raw_uid = os.environ.get("OPENENV_VALIDATION_SUBJECT_UID")
+    raw_gid = os.environ.get("OPENENV_VALIDATION_SUBJECT_GID")
+    if raw_uid is None and raw_gid is None:
+        return {}
+    if os.name != "posix" or raw_uid is None or raw_gid is None:
+        raise RuntimeError("The isolated subject identity is incomplete or unsupported")
+    try:
+        uid = int(raw_uid)
+        gid = int(raw_gid)
+    except ValueError as exc:
+        raise RuntimeError("The isolated subject identity is malformed") from exc
+    if uid <= 0 or gid <= 0:
+        raise RuntimeError("The isolated subject identity must be unprivileged")
+    return {"user": uid, "group": gid, "extra_groups": ()}
+
+
 def _ensure_port_available(port: int) -> None:
     with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as probe:
         probe.settimeout(0.25)
@@ -283,6 +301,13 @@ def _launch_environment(env_path: Path, timeout_s: float) -> Iterator[str]:
     base_url = f"http://127.0.0.1:{port}"
     _ensure_port_available(port)
     with TemporaryDirectory(prefix="openenv-validation-") as temporary_home:
+        subject_process_kwargs = _subject_process_kwargs()
+        if subject_process_kwargs:
+            os.chown(
+                temporary_home,
+                subject_process_kwargs["user"],
+                subject_process_kwargs["group"],
+            )
         process_env = _runtime_environment(
             env_path, temporary_home=Path(temporary_home)
         )
@@ -293,6 +318,7 @@ def _launch_environment(env_path: Path, timeout_s: float) -> Iterator[str]:
             stdout=subprocess.DEVNULL,
             stderr=subprocess.DEVNULL,
             start_new_session=True,
+            **subject_process_kwargs,
         )
         try:
             deadline = time.monotonic() + timeout_s
diff --git a/src/openenv/validation/remote.py b/src/openenv/validation/remote.py
index 0e3804c7d..f9f65035e 100644
--- a/src/openenv/validation/remote.py
+++ b/src/openenv/validation/remote.py
@@ -44,7 +44,7 @@
 DEFAULT_SANDBOX_FLAVOR = "cpu-basic"
 _REMOTE_REVISION_ARCHIVE = "/tmp/openenv-revision.tar.gz"
 _REMOTE_VALIDATOR_ARCHIVE = "/tmp/openenv-validator.tar.gz"
-_REMOTE_REPORT = "/workspace/validation-report.json"
+_REMOTE_REPORT = "/workspace/trusted/validation-report.json"
 _REVISION_PATTERN = re.compile(r"(?:[0-9a-f]{40}|[0-9a-f]{64})")
 _EXCLUDED_PARTS = frozenset(
     {
@@ -195,13 +195,29 @@ def _remote_command(
 runtime_timeout="$5"
 environment_root=/workspace/environment
 validator_root=/workspace/validator
-mkdir -p "$environment_root" "$validator_root" || exit 70
+trusted_root=/workspace/trusted
+subject_root=/workspace/subject
+subject_site="$subject_root/site-packages"
+subject_home="$subject_root/home"
+subject_uid=10001
+subject_gid=10001
+mkdir -p "$environment_root" "$validator_root" "$trusted_root" || exit 70
+chmod 700 "$trusted_root" || exit 70
 tar -xzf "$revision_archive" -C "$environment_root" || exit 70
 tar -xzf "$validator_archive" -C "$validator_root" || exit 70
 python -m pip install --disable-pip-version-check --no-input "$validator_root" || exit 70
-python -m pip install --disable-pip-version-check --no-input "$environment_root" || exit 71
+chown -R 0:0 "$environment_root" "$validator_root" "$trusted_root" || exit 70
+chmod -R a+rX,go-w "$environment_root" "$validator_root" || exit 70
+mkdir -p "$subject_site" "$subject_home" || exit 70
+chown -R "$subject_uid:$subject_gid" "$subject_root" || exit 70
+setpriv --reuid="$subject_uid" --regid="$subject_gid" --clear-groups \
+  env HOME="$subject_home" python -m pip install --disable-pip-version-check \
+  --no-input --target "$subject_site" "$environment_root" || exit 71
 set +e
-PYTHONPATH="$validator_root/src" python -m openenv.cli.__main__ validate \
+OPENENV_VALIDATION_SUBJECT_UID="$subject_uid" \
+OPENENV_VALIDATION_SUBJECT_GID="$subject_gid" \
+PYTHONPATH="$validator_root/src:$subject_site" \
+python -m openenv.cli.__main__ validate \
   "$environment_root" --profile "$profile" --json --output "$report_path" \
   --timeout "$runtime_timeout"
 validation_status=$?
@@ -575,5 +591,7 @@ def run_remote_validation(
             ) from exc
         finally:
             if sandbox is not None:
+                with suppress(Exception):
+                    sandbox.kill()
                 with suppress(Exception):
                     sandbox.close()
diff --git a/tests/test_validation/test_local.py b/tests/test_validation/test_local.py
index 4a9948b98..ba0574c95 100644
--- a/tests/test_validation/test_local.py
+++ b/tests/test_validation/test_local.py
@@ -13,6 +13,7 @@
 from openenv.validation.local import (
     _runtime_environment,
     _server_command,
+    _subject_process_kwargs,
     run_local_validation,
 )
 from openenv.validation.models import (
@@ -255,3 +256,19 @@ def test_server_command_honors_manifest_port(tmp_path: Path) -> None:
 def test_static_profile_rejects_url_in_public_api() -> None:
     with pytest.raises(ValueError, match="local source"):
         run_local_validation("https://example.com", profile=ValidationProfile.STATIC)
+
+
+def test_remote_subject_process_drops_to_declared_unprivileged_identity() -> None:
+    with patch.dict(
+        os.environ,
+        {
+            "OPENENV_VALIDATION_SUBJECT_UID": "10001",
+            "OPENENV_VALIDATION_SUBJECT_GID": "10002",
+        },
+        clear=False,
+    ):
+        assert _subject_process_kwargs() == {
+            "user": 10001,
+            "group": 10002,
+            "extra_groups": (),
+        }
diff --git a/tests/test_validation/test_remote.py b/tests/test_validation/test_remote.py
index 13539545e..005c5e2ae 100644
--- a/tests/test_validation/test_remote.py
+++ b/tests/test_validation/test_remote.py
@@ -187,6 +187,8 @@ def write_download(_remote_path: str, local_path: str | Path) -> None:
     command_text = " ".join(command) if isinstance(command, list) else command
     assert "publish" in command_text
     assert "validation" in command_text
+    assert "setpriv" in command_text
+    assert "/workspace/trusted/validation-report.json" in command_text
     for remote_path in uploads:
         assert remote_path in command_text
     sandbox.files.download.assert_called_once()
@@ -201,6 +203,7 @@ def write_download(_remote_path: str, local_path: str | Path) -> None:
     assert report.certified is False
     assert report.certification_eligible is False
     assert report.results[0].criterion_id == "source.validation_spec"
+    sandbox.kill.assert_called_once_with()
     sandbox.close.assert_called_once_with()
 
 
@@ -233,6 +236,7 @@ def test_remote_validation_command_failure_is_clean_and_closes_sandbox(
     assert "failed" in message
     assert "hf_1234567890abcdef" not in message
     sandbox.files.download.assert_not_called()
+    sandbox.kill.assert_called_once_with()
     sandbox.close.assert_called_once_with()
 
 
@@ -264,4 +268,5 @@ def write_download(_remote_path: str, local_path: str | Path) -> None:
     assert "report" in message
     assert "invalid" in message or "malformed" in message
     assert "not-json" not in message
+    sandbox.kill.assert_called_once_with()
     sandbox.close.assert_called_once_with()