It's a canker in the international law.
Not in any secondary laws like 12-mile sea zone, or even border inviolability.
The Minsk Conspiracy is a canker in the core principle of any community life: "Do not truth the liar".
The Minsk Agreement violates this principle twice:
1. Russia used to sign a treaty about recognising of Ukrainian borders. After Russia ignored that treaty and occupied part of Ukraine, it's not a good idea to sign with Russia a new treaty, analogous but better for Russia.
2. Russia has profit, calling its army "Donbass militia", and its agression against Ukraine - "Civil war in Ukraine". Same as any agressor has profit, camouflaging its participation in the war. This lie is repeated in the Minsk Agreement.