commit 90afb9ab8a560d43ce02975151b38e50f1f227ca
Author: Clay Gerrard <clay.gerrard@gmail.com>
Date:   Mon Dec 12 14:58:11 2022 -0600

    s3api: Prevent XXE injections
    
    Previously, clients could use XML external entities (XXEs) to read
    arbitrary files from proxy-servers and inject the content into the
    request. Since many S3 APIs reflect request content back to the user,
    this could be used to extract any secrets that the swift user could
    read, such as tempauth credentials, keymaster secrets, etc.
    
    Now, disable entity resolution -- any unknown entities will be replaced
    with an empty string. Without resolving the entities, the request is
    still processed. But a warning is logged when there are entities in the
    XML.
    
    Change-Id: I8f7370834bc2b717b6141f8e88b81a02821053b7
    Closes-Bug: #1998625
    Co-Authored-By: Romain de Joux <romain.de-joux@ovhcloud.com>

diff --git a/swift/common/middleware/s3api/etree.py b/swift/common/middleware/s3api/etree.py
index 987b84a14..e16b75340 100644
--- a/swift/common/middleware/s3api/etree.py
+++ b/swift/common/middleware/s3api/etree.py
@@ -130,7 +130,7 @@ class _Element(lxml.etree.ElementBase):
 
 
 parser_lookup = lxml.etree.ElementDefaultClassLookup(element=_Element)
-parser = lxml.etree.XMLParser()
+parser = lxml.etree.XMLParser(resolve_entities=False, no_network=True)
 parser.set_element_class_lookup(parser_lookup)
 
 Element = parser.makeelement
diff --git a/test/unit/common/middleware/s3api/test_multi_delete.py b/test/unit/common/middleware/s3api/test_multi_delete.py
index 0cfe438de..04fc63efe 100644
--- a/test/unit/common/middleware/s3api/test_multi_delete.py
+++ b/test/unit/common/middleware/s3api/test_multi_delete.py
@@ -523,6 +523,7 @@ class TestS3ApiMultiDelete(S3ApiTestCase):
                             body=body)
         status, headers, body = self.call_s3api(req)
         self.assertEqual(status.split()[0], '200')
+        self.assertIn(b'<Error><Key>Key1</Key><Code>Server Error</Code>', body)
 
     def _test_object_multi_DELETE(self, account):
         self.keys = ['Key1', 'Key2']
@@ -580,6 +581,43 @@ class TestS3ApiMultiDelete(S3ApiTestCase):
         elem = fromstring(body)
         self.assertEqual(len(elem.findall('Deleted')), len(self.keys))
 
+    def test_object_multi_DELETE_with_system_entity(self):
+        self.keys = ['Key1', 'Key2']
+        self.swift.register(
+            'DELETE', '/v1/AUTH_test/bucket/%s' % self.keys[0],
+            swob.HTTPNotFound, {}, None)
+        self.swift.register(
+            'DELETE', '/v1/AUTH_test/bucket/%s' % self.keys[1],
+            swob.HTTPNoContent, {}, None)
+
+        elem = Element('Delete')
+        for key in self.keys:
+            obj = SubElement(elem, 'Object')
+            SubElement(obj, 'Key').text = key
+        body = tostring(elem, use_s3ns=False)
+        body = body.replace(
+            b'?>\n',
+            b'?>\n<!DOCTYPE foo [<!ENTITY ent SYSTEM "file:///etc/passwd"> ]>\n',
+        ).replace(b'>Key1<', b'>Key1&ent;<')
+        content_md5 = (
+            base64.b64encode(md5(body, usedforsecurity=False).digest())
+            .strip())
+
+        req = Request.blank('/bucket?delete',
+                            environ={'REQUEST_METHOD': 'POST'},
+                            headers={'Authorization': 'AWS test:full_control:hmac',
+                                     'Date': self.get_date_header(),
+                                     'Content-MD5': content_md5},
+                            body=body)
+        req.date = datetime.now()
+        req.content_type = 'text/plain'
+
+        status, headers, body = self.call_s3api(req)
+        self.assertEqual(status, '200 OK', body)
+        self.assertIn(b'<Deleted><Key>Key2</Key></Deleted>', body)
+        self.assertNotIn(b'root:/root', body)
+        self.assertIn(b'<Deleted><Key>Key1</Key></Deleted>', body)
+
     def _test_no_body(self, use_content_length=False,
                       use_transfer_encoding=False, string_to_md5=b''):
         content_md5 = (base64.b64encode(