diff --git a/Lib/httplib.py b/Lib/httplib.py
index 9c8c5eedccb04a3..6271c76f741dcaf 100644
--- a/Lib/httplib.py
+++ b/Lib/httplib.py
@@ -261,6 +261,11 @@
 # to prevent http header injection.
 _contains_disallowed_method_pchar_re = re.compile('[\x00-\x1f]')
 
+# RFC 9112: Content-Length = 1*DIGIT and chunk-size = 1*HEXDIG.
+# int() is more permissive, so we match against the grammar before calling it.
+_is_legal_content_length = re.compile(r'[0-9]+\Z').match
+_is_legal_chunk_size = re.compile(r'[0-9a-fA-F]+\Z').match
+
 # We always set the Content-Length header for these methods because some
 # servers will otherwise respond with a 411
 _METHODS_EXPECTING_BODY = {'PATCH', 'POST', 'PUT'}
@@ -503,14 +508,12 @@ def begin(self):
         # do we have a Content-Length?
         # NOTE: RFC 2616, S4.4, #3 says we ignore this if tr_enc is "chunked"
         length = self.msg.getheader('content-length')
-        if length and not self.chunked:
-            try:
-                self.length = int(length)
-            except ValueError:
-                self.length = None
-            else:
-                if self.length < 0:  # ignore nonsensical negative lengths
-                    self.length = None
+        if length is not None:
+            # RFC 9112, section 5.1: optional whitespace (SP / HTAB) around
+            # the field value is not part of the value.
+            length = length.strip(' \t')
+        if length and not self.chunked and _is_legal_content_length(length):
+            self.length = int(length)
         else:
             self.length = None
 
@@ -632,7 +635,10 @@ def _read_chunked(self, amt):
                 i = line.find(';')
                 if i >= 0:
                     line = line[:i] # strip chunk-extensions
+                line = line.rstrip()
                 try:
+                    if not _is_legal_chunk_size(line):
+                        raise ValueError("invalid chunk size")
                     chunk_left = int(line, 16)
                 except ValueError:
                     # close the connection as protocol synchronisation is
diff --git a/Lib/test/test_httplib.py b/Lib/test/test_httplib.py
index e7ee76b0226d096..dfd0e79075eed07 100644
--- a/Lib/test/test_httplib.py
+++ b/Lib/test/test_httplib.py
@@ -622,6 +622,46 @@ def test_negative_content_length(self):
         self.assertEqual(resp.read(), 'Hello\r\n')
         self.assertTrue(resp.isclosed())
 
+    def test_malformed_content_length(self):
+        # RFC 9112: Content-Length = 1*DIGIT.  Values that int() accepts but
+        # the grammar forbids must not be used to frame the body.
+        for value in ('+5', '5_0', '5 0', '0x5'):
+            sock = FakeSocket(
+                'HTTP/1.1 200 OK\r\nContent-Length: %s\r\n\r\nHello\r\n' % value)
+            resp = httplib.HTTPResponse(sock, method="GET")
+            resp.begin()
+            self.assertIsNone(resp.length, value)
+            self.assertEqual(resp.read(), 'Hello\r\n')
+            resp.close()
+
+    def test_content_length_with_whitespace(self):
+        # RFC 9112, section 5.1: optional whitespace (SP / HTAB) around
+        # the field value is not part of the value, so it must not
+        # prevent the Content-Length from being used to frame the body.
+        for value in ('7 ', '7\t', '7 \t ', ' 7 '):
+            sock = FakeSocket(
+                'HTTP/1.1 200 OK\r\nContent-Length: %s\r\n\r\n'
+                'Hello\r\nextra' % value)
+            resp = httplib.HTTPResponse(sock, method="GET")
+            resp.begin()
+            self.assertEqual(resp.length, 7, repr(value))
+            self.assertEqual(resp.read(), 'Hello\r\n')
+            self.assertTrue(resp.isclosed())
+            resp.close()
+
+    def test_malformed_chunk_size(self):
+        # RFC 9112: chunk-size = 1*HEXDIG.  Reject sizes that int(_, 16) accepts
+        # but the grammar forbids (a sign, an "0x" prefix or leading
+        # whitespace).
+        start = 'HTTP/1.1 200 OK\r\nTransfer-Encoding: chunked\r\n\r\n'
+        for size in ('-5', '+5', '0x5', ' 5'):
+            sock = FakeSocket(start + '%s\r\nHELLO\r\n0\r\n\r\n' % size)
+            resp = httplib.HTTPResponse(sock, method="GET")
+            resp.begin()
+            self.assertRaises(httplib.IncompleteRead, resp.read)
+            self.assertTrue(resp.isclosed(), size)
+            resp.close()
+
     def test_incomplete_read(self):
         sock = FakeSocket('HTTP/1.1 200 OK\r\nContent-Length: 10\r\n\r\nHello\r\n')
         resp = httplib.HTTPResponse(sock, method="GET")