Vyper is a pythonic Smart Contract Language for the Ethereum virtual machine. Prior to version 0.3.0, default functions dont respect nonreentrancy keys and the lock isnt emitted. No vulnerable production contracts were found. Additionally, using a lock on a default function is a very sparsely used pattern. As such, the impact is low. Version 0.3.0 contains a patch for the issue.
The product does not properly acquire or release a lock on a resource, leading to unexpected resource state changes and behaviors.
Locking is a type of synchronization behavior that ensures that multiple independently-operating processes or threads do not interfere with each other when accessing the same resource. All processes/threads are expected to follow the same steps for locking. If these steps are not followed precisely - or if no locking is done at all - then another process/thread could modify the shared resource in a way that is not visible or predictable to the original process. This can lead to data or memory corruption, denial of service, etc.