The claim that Mario Canales Najjar, president of the Mexican Hunting Federation, was killed by a buffalo he shot in Entre Ríos, Argentina is mostly true because multiple reliable sources confirm the fatal attack by a buffalo during a hunting trip there; however, the detail about the reserve lacking permits for big game is not clearly supported or mentioned in the available sources.
Mexican Hunting Federation president Mario Canales Najjar, 64, was killed by a buffalo he shot in Entre Ríos, Argentina. The hunt took place at a reserve lacking permits for big game.

Mario Alberto Canales Najjar: Head of Mexican Hunting Federation killed by charging buffalo in Argentina - International | EL PAÍS English
Source: english.elpais.com
Key Evidence
EL PAÍS confirms Canales Najjar was killed by a charging buffalo in Entre Ríos during a hunt.
english.elpais.comenglish.elpais.comMario Alberto Canales Najjar: Head of Mexican Hunting Federation killed by...
Marca and MercoPress corroborate the fatal attack by a buffalo he had shot at in Argentina.
marca.commarca.comThe president of the Mexican Hunting Federation killed by a buffalo he shot at
en.mercopress.comen.mercopress.comPresident of the Mexican Hunting Federation dies in Argentina after being rammed...
None of the sources mention any issues with permits or legality of the hunting reserve.
What the Evidence Shows
Multiple independent and reputable news outlets, including EL PAÍS, Marca, and MercoPress, report that Mario Alberto Canales Najjar, aged 64 and president of the Mexican Hunting Federation, died on October 7, 2022, after being gored by a buffalo he had shot at during a hunting expedition in the province of Entre Ríos, Argentina. The incident involved a large buffalo charging and repeatedly ramming him, leading to fatal injuries. The sources consistently agree on the key facts: Canales Najjar was hunting in Entre Ríos, Argentina; he shot at a buffalo; the buffalo charged and fatally injured him. The date and location are consistent across reports. However, none of the reviewed sources explicitly mention that the hunting reserve lacked permits for big game hunting or that the hunt was illegal or unauthorized. This specific claim about permits is absent from all major news reports and official statements cited. Therefore, while the core event is well-documented and verified, the assertion regarding permit status remains unverified based on available evidence.english.elpais.comenglish.elpais.comMario Alberto Canales Najjar: Head of Mexican Hunting Federation killed by...
marca.commarca.comThe president of the Mexican Hunting Federation killed by a buffalo he shot at+1 more
In summary:
Verified: Mario Canales Najjar was killed by a buffalo he shot in Entre Ríos during a hunting trip.
Unverified: The reserve lacked permits for big game hunting.
This distinction is important to maintain accuracy and avoid spreading unconfirmed information.