https://github.com/python/cpython/commit/6c922bbe28f2cd901ffa749240f96449287771a6 commit: 6c922bbe28f2cd901ffa749240f96449287771a6 branch: 3.13 author: Miss Islington (bot) <[email protected]> committer: serhiy-storchaka <[email protected]> date: 2025-12-01T14:22:10Z summary:
[3.13] gh-119452: Fix a potential virtual memory allocation denial of service in http.server (GH-119455) (GH-142130) 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, so that the memory consumption is proportional to the amount of sent data. (cherry picked from commit 29c657a1f231c0908796e0c9ff6967e15ab20d9b) Co-authored-by: Serhiy Storchaka <[email protected]> files: A Misc/NEWS.d/next/Security/2024-05-23-11-44-41.gh-issue-119452.PRfsSv.rst M Lib/http/server.py M Lib/test/test_httpservers.py diff --git a/Lib/http/server.py b/Lib/http/server.py index 758a725f1fd540..f9d676c8eb1861 100644 --- a/Lib/http/server.py +++ b/Lib/http/server.py @@ -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 @@ -1234,7 +1238,16 @@ 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 and + select.select([self.rfile._sock], [], [], 0)[0]): + cursize = len(data) + # This is a geometric increase in read size (never more + # than doubling our the current length of data per loop + # iteration). + delta = min(cursize, nbytes - cursize) + data += self.rfile.read(delta) 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 c369baf28fe823..9e69f6f6d75dec 100644 --- a/Lib/test/test_httpservers.py +++ b/Lib/test/test_httpservers.py @@ -802,6 +802,20 @@ def test_path_without_leading_slash(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).") @@ -841,6 +855,8 @@ 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. @@ -895,6 +911,11 @@ 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): @@ -917,6 +938,8 @@ 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) @@ -989,6 +1012,21 @@ 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): + 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 00000000000000..98956627f2b30d --- /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. _______________________________________________ Python-checkins mailing list -- [email protected] To unsubscribe send an email to [email protected] https://mail.python.org/mailman3//lists/python-checkins.python.org Member address: [email protected]
