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[3.12] gh-119452: Fix a potential virtual memory allocation denial of service in http.server (GH-142216) #142297

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Merged

Yhg1s merged 1 commit into python:3.12 from miss-islington:backport-0e4f4f1-3.12

Dec 15, 2025

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[3.12] gh-119452: Fix a potential virtual memory allocation denial of service in http.server (GH-142216) #142297

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03afece

[3.14] gh-119452: Fix a potential virtual memory allocation denial of…

serhiy-storchaka Dec 5, 2025

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[3.14] gh-119452: Fix a potential virtual memory allocation denial of…

… service in http.server (GH-142216)

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.
(cherry picked from commit 0e4f4f1)

Co-authored-by: Serhiy Storchaka <[email protected]>

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serhiy-storchaka authored and miss-islington committed Dec 5, 2025

commit 03afeceffba262c8bb170cfa04cbff614d018077

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17 changes: 16 additions & 1 deletion 17 Lib/http/server.py

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Original file line number	Diff line number	Diff line change
Expand Up		@@ -127,6 +127,10 @@

		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 = 1 # Seems to make sense in testing environment
Expand Down Expand Up		@@ -1218,7 +1222,18 @@ def run_cgi(self):
		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]
Expand Down

39 changes: 39 additions & 0 deletions 39 Lib/test/test_httpservers.py

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Original file line number	Diff line number	Diff line change
Expand Up		@@ -695,6 +695,20 @@ def test_html_escape_filename(self):
		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).")
Expand Down Expand Up		@@ -728,6 +742,8 @@ def setUp(self):
		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.
Expand Down Expand Up		@@ -782,6 +798,11 @@ def setUp(self):
		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):
Expand All		@@ -803,6 +824,8 @@ def tearDown(self):
		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)
Expand Down Expand Up		@@ -875,6 +898,22 @@ def test_post(self):

		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()
Expand Down

5 changes: 5 additions & 0 deletions 5 Misc/NEWS.d/next/Security/2024-05-23-11-44-41.gh-issue-119452.PRfsSv.rst

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Original file line number	Diff line number	Diff line change
		@@ -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.

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