diff --git a/.changes/next-release/bugfix-s3streamingoutput-59585.json b/.changes/next-release/bugfix-s3streamingoutput-59585.json
new file mode 100644
index 000000000000..e34eeb66de1b
--- /dev/null
+++ b/.changes/next-release/bugfix-s3streamingoutput-59585.json
@@ -0,0 +1,5 @@
+{
+  "type": "bugfix",
+  "category": "s3, streaming output",
+  "description": "Output files created by S3 Select and streaming output commands are now created with owner-only permissions (0600). Existing files are also tightened to 0600 when overwritten."
+}
diff --git a/awscli/customizations/s3events.py b/awscli/customizations/s3events.py
index 2cd57fef7975..50818865e31b 100644
--- a/awscli/customizations/s3events.py
+++ b/awscli/customizations/s3events.py
@@ -13,6 +13,7 @@
 """Add S3 specific event streaming output arg."""
 
 import os
+import stat
 
 from awscli.arguments import CustomArgument
 
@@ -124,7 +125,9 @@ def save_file(self, parsed, **kwargs):
         fd = os.open(
             self._output_file, os.O_WRONLY | os.O_CREAT | os.O_TRUNC, 0o600
         )
-        os.chmod(self._output_file, 0o600)
+        if stat.S_ISREG(os.fstat(fd).st_mode):
+            # Only chmod regular files; skip special files like /dev/null
+            os.chmod(self._output_file, 0o600)
         with os.fdopen(fd, 'wb') as fp:
             for event in event_stream:
                 if 'Records' in event:
diff --git a/awscli/customizations/streamingoutputarg.py b/awscli/customizations/streamingoutputarg.py
index 596aab8a3342..fe23bd7a5195 100644
--- a/awscli/customizations/streamingoutputarg.py
+++ b/awscli/customizations/streamingoutputarg.py
@@ -11,6 +11,7 @@
 # ANY KIND, either express or implied. See the License for the specific
 # language governing permissions and limitations under the License.
 import os
+import stat
 
 from botocore.model import Shape
 
@@ -109,7 +110,9 @@ def save_file(self, parsed, **kwargs):
         fd = os.open(
             self._output_file, os.O_WRONLY | os.O_CREAT | os.O_TRUNC, 0o600
         )
-        os.chmod(self._output_file, 0o600)
+        if stat.S_ISREG(os.fstat(fd).st_mode):
+            # Only chmod regular files; skip special files like /dev/null
+            os.chmod(self._output_file, 0o600)
         with os.fdopen(fd, 'wb') as fp:
             data = body.read(buffer_size)
             while data:
diff --git a/tests/functional/s3api/test_select_object_content.py b/tests/functional/s3api/test_select_object_content.py
index e9078aa4b677..b5b7c33b48a0 100644
--- a/tests/functional/s3api/test_select_object_content.py
+++ b/tests/functional/s3api/test_select_object_content.py
@@ -108,6 +108,27 @@ def test_output_file_permissions(self):
         # Mask file type bits to isolate permission bits (rwxrwxrwx)
         self.assertEqual(os.stat(filename).st_mode & 0o777, 0o600)
 
+    @skip_if_windows('chmod is not supported on Windows')
+    def test_output_does_not_chmod_non_regular_files(self):
+        cmdline = self.prefix + [
+            '--bucket',
+            'mybucket',
+            '--key',
+            'mykey',
+            '--expression',
+            'SELECT * FROM S3Object',
+            '--expression-type',
+            'SQL',
+            '--input-serialization',
+            '{"CSV": {}}',
+            '--output-serialization',
+            '{"CSV": {}}',
+            '/dev/null',
+        ]
+        original_mode = os.stat('/dev/null').st_mode & 0o777
+        self.assert_params_for_cmd(cmdline, ignore_params=True)
+        self.assertEqual(os.stat('/dev/null').st_mode & 0o777, original_mode)
+
     def test_errors_are_propagated(self):
         self.http_response.status_code = 400
         self.parsed_response = {
diff --git a/tests/functional/test_streaming_output.py b/tests/functional/test_streaming_output.py
index 3255e7b74e9a..7fbb9980a6a0 100644
--- a/tests/functional/test_streaming_output.py
+++ b/tests/functional/test_streaming_output.py
@@ -62,3 +62,17 @@ def test_streaming_output_file_permissions(self):
         self.assert_params_for_cmd(cmdline % outpath, ignore_params=True)
         # Mask file type bits to isolate permission bits (rwxrwxrwx)
         self.assertEqual(os.stat(outpath).st_mode & 0o777, 0o600)
+
+    @skip_if_windows('chmod is not supported on Windows')
+    def test_streaming_output_does_not_chmod_non_regular_files(self):
+        cmdline = (
+            'kinesis-video-media get-media --stream-name test-stream '
+            '--start-selector StartSelectorType=EARLIEST %s'
+        )
+        self.parsed_response = {
+            'ContentType': 'video/webm',
+            'Payload': BytesIO(b'testbody'),
+        }
+        original_mode = os.stat('/dev/null').st_mode & 0o777
+        self.assert_params_for_cmd(cmdline % '/dev/null', ignore_params=True)
+        self.assertEqual(os.stat('/dev/null').st_mode & 0o777, original_mode)