[3.14] gh-119452: Fix a potential virtual memory allocation denial of service in...

The CGI server on Windows could consume the amount of memory specified
in the Content-Length header of the request even if the client does not
send such much data. Now it reads the POST request body by chunks,
therefore the memory consumption is proportional to the amount of sent
data.

diff --git a/Lib/http/server.py b/Lib/http/server.py
index 8bb49275e78cbd3c1207780af216f9b3f217e737..ac1f57c29f06ff7de8219cf243a3a8f6d5dd9053 100644 (file)
--- a/Lib/http/server.py
+++ b/Lib/http/server.py
@@ -134,6 +134,10 @@ DEFAULT_ERROR_MESSAGE = """\
 
 DEFAULT_ERROR_CONTENT_TYPE = "text/html;charset=utf-8"
 
+# Data larger than this will be read in chunks, to prevent extreme
+# overallocation.
+_MIN_READ_BUF_SIZE = 1 << 20
+
 class HTTPServer(socketserver.TCPServer):
 
     allow_reuse_address = True    # Seems to make sense in testing environment
@@ -1284,7 +1288,18 @@ class CGIHTTPRequestHandler(SimpleHTTPRequestHandler):
                                  env = env
                                  )
             if self.command.lower() == "post" and nbytes > 0:
-                data = self.rfile.read(nbytes)
+                cursize = 0
+                data = self.rfile.read(min(nbytes, _MIN_READ_BUF_SIZE))
+                while len(data) < nbytes and len(data) != cursize:
+                    cursize = len(data)
+                    # This is a geometric increase in read size (never more
+                    # than doubling out the current length of data per loop
+                    # iteration).
+                    delta = min(cursize, nbytes - cursize)
+                    try:
+                        data += self.rfile.read(delta)
+                    except TimeoutError:
+                        break
             else:
                 data = None
             # throw away additional data [see bug #427345]

diff --git a/Lib/test/test_httpservers.py b/Lib/test/test_httpservers.py
index 9539457d4d829da96783a60f65516c857a6141ab..7b58c5ef55b3379ea33a5e78428a88c98b5e67ec 100644 (file)
--- a/Lib/test/test_httpservers.py
+++ b/Lib/test/test_httpservers.py
@@ -913,6 +913,20 @@ for k, v in os.environ.items():
 print("</pre>")
 """
 
+cgi_file7 = """\
+#!%s
+import os
+import sys
+
+print("Content-type: text/plain")
+print()
+
+content_length = int(os.environ["CONTENT_LENGTH"])
+body = sys.stdin.buffer.read(content_length)
+
+print(f"{content_length} {len(body)}")
+"""
+
 
 @unittest.skipIf(hasattr(os, 'geteuid') and os.geteuid() == 0,
         "This test can't be run reliably as root (issue #13308).")
@@ -952,6 +966,8 @@ class CGIHTTPServerTestCase(BaseTestCase):
         self.file3_path = None
         self.file4_path = None
         self.file5_path = None
+        self.file6_path = None
+        self.file7_path = None
 
         # The shebang line should be pure ASCII: use symlink if possible.
         # See issue #7668.
@@ -1006,6 +1022,11 @@ class CGIHTTPServerTestCase(BaseTestCase):
             file6.write(cgi_file6 % self.pythonexe)
         os.chmod(self.file6_path, 0o777)
 
+        self.file7_path = os.path.join(self.cgi_dir, 'file7.py')
+        with open(self.file7_path, 'w', encoding='utf-8') as file7:
+            file7.write(cgi_file7 % self.pythonexe)
+        os.chmod(self.file7_path, 0o777)
+
         os.chdir(self.parent_dir)
 
     def tearDown(self):
@@ -1028,6 +1049,8 @@ class CGIHTTPServerTestCase(BaseTestCase):
                 os.remove(self.file5_path)
             if self.file6_path:
                 os.remove(self.file6_path)
+            if self.file7_path:
+                os.remove(self.file7_path)
             os.rmdir(self.cgi_child_dir)
             os.rmdir(self.cgi_dir)
             os.rmdir(self.cgi_dir_in_sub_dir)
@@ -1100,6 +1123,22 @@ class CGIHTTPServerTestCase(BaseTestCase):
 
         self.assertEqual(res.read(), b'1, python, 123456' + self.linesep)
 
+    def test_large_content_length(self):
+        for w in range(15, 25):
+            size = 1 << w
+            body = b'X' * size
+            headers = {'Content-Length' : str(size)}
+            res = self.request('/cgi-bin/file7.py', 'POST', body, headers)
+            self.assertEqual(res.read(), b'%d %d' % (size, size) + self.linesep)
+
+    def test_large_content_length_truncated(self):
+        with support.swap_attr(self.request_handler, 'timeout', 0.001):
+            for w in range(18, 65):
+                size = 1 << w
+                headers = {'Content-Length' : str(size)}
+                res = self.request('/cgi-bin/file1.py', 'POST', b'x', headers)
+                self.assertEqual(res.read(), b'Hello World' + self.linesep)
+
     def test_invaliduri(self):
         res = self.request('/cgi-bin/invalid')
         res.read()

diff --git a/Misc/NEWS.d/next/Security/2024-05-23-11-44-41.gh-issue-119452.PRfsSv.rst b/Misc/NEWS.d/next/Security/2024-05-23-11-44-41.gh-issue-119452.PRfsSv.rst
new file mode 100644 (file)
index 0000000..9895662
--- /dev/null
+++ b/Misc/NEWS.d/next/Security/2024-05-23-11-44-41.gh-issue-119452.PRfsSv.rst
@@ -0,0 +1,5 @@
+Fix a potential memory denial of service in the :mod:`http.server` module.
+When a malicious user is connected to the CGI server on Windows, it could cause
+an arbitrary amount of memory to be allocated.
+This could have led to symptoms including a :exc:`MemoryError`, swapping, out
+of memory (OOM) killed processes or containers, or even system crashes.