CVE-2023-2975

Issue summary: The AES-SIV cipher implementation contains a bug that causesit to ignore empty associated data entries which are unauthenticated asa consequence.

Impact summary: Applications that use the AES-SIV algorithm and want toauthenticate empty data entries as associated data can be misled by removing,adding or reordering such empty entries as these are ignored by the OpenSSLimplementation. We are currently unaware of any such applications.

The AES-SIV algorithm allows for authentication of multiple associateddata entries along with the encryption. To authenticate empty data theapplication has to call EVP_EncryptUpdate() (or EVP_CipherUpdate()) withNULL pointer as the output buffer and 0 as the input buffer length.The AES-SIV implementation in OpenSSL just returns success for such a callinstead 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 andwe expect it to be rare for an application to use empty associated dataentries this is qualified as Low severity issue.