Previously, Cipher.update_into would accept Python objects which implement the buffer protocol, but provide only immutable buffers:
>>> outbuf = b"\x00" * 32
>>> c = ciphers.Cipher(AES(b"\x00" * 32), modes.ECB()).encryptor()
>>> c.update_into(b"\x00" * 16, outbuf)
16
>>> outbuf
b'\xdc\x95\xc0x\xa2@\x89\x89\xadH\xa2\x14\x92\x84 \x87\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'
This would allow immutable objects (such as bytes) to be mutated, thus violating fundamental rules of Python. This is a soundness bug -- it allows programmers to misuse an API, it cannot be exploited by attacker controlled data alone.
This now correctly raises an exception.
This issue has been present since update_into was originally introduced in cryptography 1.8.
Previously,
Cipher.update_intowould accept Python objects which implement the buffer protocol, but provide only immutable buffers:This would allow immutable objects (such as
bytes) to be mutated, thus violating fundamental rules of Python. This is a soundness bug -- it allows programmers to misuse an API, it cannot be exploited by attacker controlled data alone.This now correctly raises an exception.
This issue has been present since
update_intowas originally introduced in cryptography 1.8.