OpenSSL Security Advisory [14th July 2023]
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AES-SIV implementation ignores empty associated data entries (CVE-2023-2975)
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Severity: Low

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.

OpenSSL versions 3.0.0 to 3.0.9, and 3.1.0 to 3.1.1 are vulnerable to this
issue. The FIPS provider is not affected as the AES-SIV algorithm is not
FIPS approved and FIPS provider does not implement it.

OpenSSL versions 1.1.1 and 1.0.2 are not affected by this issue.

Due to the low severity of this issue we are not issuing new releases of
OpenSSL at this time. The fix will be included in the next releases when they
become available. The fix is also available in commit 6a83f0c9 (for 3.1) and
commit 00e2f5ee (for 3.0) in the OpenSSL git repository.

This issue was reported on 16th May 2023 by Juerg Wullschleger (Google).
The fix was developed by Tomas Mraz.

General Advisory Notes
======================

URL for this Security Advisory:
https://www.openssl.org/news/secadv/20230714.txt

Note: the online version of the advisory may be updated with additional details
over time.

For details of OpenSSL severity classifications please see:
https://www.openssl.org/policies/secpolicy.html

OpenSSL 1.1.1 will reach end-of-life on 2023-09-11. After that date security
fixes for 1.1.1 will only be available to premium support customers.