https://github.com/python/cpython/commit/67f4d53425d4f7df559b4a0ba5bfb66e795854c7
commit: 67f4d53425d4f7df559b4a0ba5bfb66e795854c7
branch: main
author: Serhiy Storchaka <[email protected]>
committer: serhiy-storchaka <[email protected]>
date: 2026-08-21T10:50:25Z
summary:
gh-156166: Fix setting and deleting SSLContext._msg_callback (GH-156167)
The setter released the old callback before validating the new value,
so a failed assignment or a deletion removed it.
files:
A Misc/NEWS.d/next/Library/2026-08-21-13-30-00.gh-issue-156166.Xv8pQm.rst
M Lib/test/test_ssl.py
M Modules/_ssl/debughelpers.c
diff --git a/Lib/test/test_ssl.py b/Lib/test/test_ssl.py
index 14e4620669491f..285bcac65ab57b 100644
--- a/Lib/test/test_ssl.py
+++ b/Lib/test/test_ssl.py
@@ -5598,6 +5598,18 @@ def msg_cb(conn, direction, version, content_type,
msg_type, data):
with self.assertRaises(TypeError):
client_context._msg_callback = object()
+ # the attribute of the underlying C type accepts only a callable
+ # and cannot be deleted
+ descr = _ssl._SSLContext.__dict__['_msg_callback']
+ with self.assertRaises(TypeError):
+ descr.__set__(client_context, object())
+ # a failed assignment does not change the value
+ self.assertIs(client_context._msg_callback, msg_cb)
+ with self.assertRaisesRegex(AttributeError, 'cannot be deleted'):
+ descr.__delete__(client_context)
+ # a failed deletion does not change the value
+ self.assertIs(client_context._msg_callback, msg_cb)
+
def test_msg_callback_exception(self):
client_context, server_context, hostname = testing_context()
diff --git
a/Misc/NEWS.d/next/Library/2026-08-21-13-30-00.gh-issue-156166.Xv8pQm.rst
b/Misc/NEWS.d/next/Library/2026-08-21-13-30-00.gh-issue-156166.Xv8pQm.rst
new file mode 100644
index 00000000000000..2417479d333e3e
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-08-21-13-30-00.gh-issue-156166.Xv8pQm.rst
@@ -0,0 +1,3 @@
+:mod:`ssl`: A failed assignment or deletion of the ``_msg_callback``
+attribute of :class:`ssl.SSLContext` no longer removes the current callback.
+Deleting it now raises :exc:`AttributeError` instead of :exc:`TypeError`.
diff --git a/Modules/_ssl/debughelpers.c b/Modules/_ssl/debughelpers.c
index b2d552f97e5b0e..e8da76907971ed 100644
--- a/Modules/_ssl/debughelpers.c
+++ b/Modules/_ssl/debughelpers.c
@@ -102,20 +102,28 @@ _PySSLContext_set_msg_callback(PyObject *op, PyObject
*arg,
void *Py_UNUSED(closure))
{
PySSLContext *self = PySSLContext_CAST(op);
- Py_CLEAR(self->msg_cb);
+ if (arg == NULL) {
+ PyErr_Format(PyExc_AttributeError,
+ "attribute '_msg_callback' of '%.100s' objects "
+ "cannot be deleted", Py_TYPE(op)->tp_name);
+ return -1;
+ }
+ if (arg != Py_None && !PyCallable_Check(arg)) {
+ PyErr_SetString(PyExc_TypeError,
+ "not a callable object");
+ return -1;
+ }
+ /* Releasing the old callback can run arbitrary code. */
+ PyObject *old_cb = self->msg_cb;
if (arg == Py_None) {
+ self->msg_cb = NULL;
SSL_CTX_set_msg_callback(self->ctx, NULL);
}
else {
- if (!PyCallable_Check(arg)) {
- SSL_CTX_set_msg_callback(self->ctx, NULL);
- PyErr_SetString(PyExc_TypeError,
- "not a callable object");
- return -1;
- }
self->msg_cb = Py_NewRef(arg);
SSL_CTX_set_msg_callback(self->ctx, _PySSL_msg_callback);
}
+ Py_XDECREF(old_cb);
return 0;
}
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