CVE-2023-2975

Issue summary: The AES-SIV cipher implementation contains a bug that causes

it to ignore empty associated data entries which are unauthenticated as

a consequence.

Impact summary: Applications that use the AES-SIV algorithm and want to

authenticate empty data entries as associated data can be misled by removing,

adding or reordering such empty entries as these are ignored by the OpenSSL

implementation. We are currently unaware of any such applications.

The AES-SIV algorithm allows for authentication of multiple associated

data entries along with the encryption. To authenticate empty data the

application has to call EVP_EncryptUpdate() (or EVP_CipherUpdate()) with

NULL pointer as the output buffer and 0 as the input buffer length.

The AES-SIV implementation in OpenSSL just returns success for such a call

instead of performing the associated data authentication operation.

The empty data thus will not be authenticated.

As this issue does not affect non-empty associated data authentication and

we expect it to be rare for an application to use empty associated data

entries this is qualified as Low severity issue.