From 9303573c74256de141831229cfa046b00e37e2c8 Mon Sep 17 00:00:00 2001 From: "Miss Islington (bot)" <31488909+miss-islington@users.noreply.github.com> Date: Fri, 5 Dec 2025 16:37:09 +0100 Subject: [PATCH] [3.13] gh-119452: Fix a potential virtual memory allocation denial of service in http.server (GH-142216) (#142296) [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 0e4f4f1a4633f2d215fb5a803cae278aeea31845) Co-authored-by: Serhiy Storchaka Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com> --- Lib/http/server.py | 17 +++++++- Lib/test/test_httpservers.py | 39 +++++++++++++++++++ ...-05-23-11-44-41.gh-issue-119452.PRfsSv.rst | 5 +++ 3 files changed, 60 insertions(+), 1 deletion(-) create mode 100644 Misc/NEWS.d/next/Security/2024-05-23-11-44-41.gh-issue-119452.PRfsSv.rst diff --git a/Lib/http/server.py b/Lib/http/server.py index 758a725f1fd5..0ec479003a47 100644 --- a/Lib/http/server.py +++ b/Lib/http/server.py @@ -127,6 +127,10 @@ 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 = 1 # Seems to make sense in testing environment @@ -1234,7 +1238,18 @@ 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 c369baf28fe8..0022e0e5d718 100644 --- a/Lib/test/test_httpservers.py +++ b/Lib/test/test_httpservers.py @@ -802,6 +802,20 @@ for k, v in os.environ.items(): print("") """ +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).") @@ -841,6 +855,8 @@ 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. @@ -895,6 +911,11 @@ 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): @@ -917,6 +938,8 @@ 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) @@ -989,6 +1012,22 @@ 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 index 000000000000..98956627f2b3 --- /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. -- 2.47.3