### Impact
An attacker could crash the server by sending malformed JWT JSON in `LoginPacket` due to a security vulnerability in [`netresearch/jsonmapper`](https://github.com/cweiske/JsonMapper), due to accepting `NULL` values in arrays whose types do not expect `NULL`.

### Patches
This problem was fixed in 5.3.1 and 4.23.1 by updating JsonMapper to include the following commit: pmmp/netresearch-jsonmapper@4f90e8dab1c9df331fad7d3d89823404e882668c

### Workarounds
A plugin may handle `DataPacketReceiveEvent` for `LoginPacket` and check that none of the input arrays contain `NULL` where it’s not expected, but this is rather cumbersome.Read More