The data leak occurred on late Monday, which was qualified as an "ethical offense" by the Elysee Palace. A medical worker having access to the database of those vaccinated against COVID-19 presumably copied Macron's QR-code and then left it available, intentionally or not.
The QR-code was deactivated so that it can never be used again.
The French agency for illness insurance, CNAM, responsible for the digital vaccination system, has already addressed the national medical council with a request to hold those responsible for the leak accountable.
In July, Macron announced new measures to curb the spread of the coronavirus, including special health passes indicating if the bearer has been vaccinated or has had a negative COVID-19 test result. The passes are obligatory in restaurants, bars, shopping centers, airplanes, all public events attended by over fifty people and long-distance trains in all parts of France.