Vulnerability affects unpatched MikroTik equipment that routes IPv6 packets. To bring the system down, all an attacker has to do is send a specific string of packets that would increase RAM usage on the router. The latest updates for the operating system are meant to address the problem, but they do not have the same effect on all devices. To fix it, the new RouterOS can calculate the cache size based on the memory available on the device. The fix is present in the current stable (v6.44.2) and long term (v 6.43.14) release versions of RouterOS.
Source: https://www.bleepingcomputer.com/news/security/year-old-dos-vulnerability-allows-attacks-on-some-mikrotik-routers/