diff --git a/scripts/ci/sandboxed_web_e2e.py b/scripts/ci/sandboxed_web_e2e.py
index b0376c0822..9bca4a1522 100644
--- a/scripts/ci/sandboxed_web_e2e.py
+++ b/scripts/ci/sandboxed_web_e2e.py
@@ -240,6 +240,7 @@ def _probe_isolation_capability(backend: str) -> None:
                 text=True,
                 timeout=10,
                 check=False,
+                shell=False,
             )
         except (OSError, subprocess.TimeoutExpired) as exc:
             raise RuntimeError(f"bubblewrap capability probe could not run: {exc}") from exc
diff --git a/tests/test_sandboxed_web_e2e.py b/tests/test_sandboxed_web_e2e.py
index 1b1cdf3722..5f271af383 100644
--- a/tests/test_sandboxed_web_e2e.py
+++ b/tests/test_sandboxed_web_e2e.py
@@ -1396,6 +1396,7 @@ def test_probe_isolation_capability_exercises_the_same_operations_as_real_comman
 
     def _fake_run(command, **kwargs):
         captured["command"] = command
+        captured["kwargs"] = kwargs
         return subprocess.CompletedProcess(command, 0, stdout="", stderr="")
 
     monkeypatch.setattr(sandboxed_web_e2e.subprocess, "run", _fake_run)
@@ -1408,6 +1409,7 @@ def _fake_run(command, **kwargs):
     assert "--bind" in command
     assert sandboxed_web_e2e.SANDBOX_MOUNT in command
     assert "--chdir" in command
+    assert captured["kwargs"].get("shell") is False
 
 
 def test_probe_isolation_capability_ignores_path_shadowed_shell(monkeypatch, tmp_path):
@@ -1434,6 +1436,7 @@ def test_probe_isolation_capability_ignores_path_shadowed_shell(monkeypatch, tmp
 
     def _fake_run(command, **kwargs):
         captured["command"] = command
+        captured["kwargs"] = kwargs
         return subprocess.CompletedProcess(command, 0, stdout="", stderr="")
 
     monkeypatch.setattr(sandboxed_web_e2e.subprocess, "run", _fake_run)
@@ -1443,6 +1446,7 @@ def _fake_run(command, **kwargs):
     probe_executable = command[-3]
     assert probe_executable in sandboxed_web_e2e.PROBE_SHELL_PATHS
     assert probe_executable != str(shadow_sh)
+    assert captured["kwargs"].get("shell") is False
 
 
 def test_probe_shell_fails_clearly_when_no_mounted_shell_exists(monkeypatch, tmp_path):