I'm just asking myself if there is a way to even check it or if a wrong and way too high number can somehow cause problems and should perhaps be considered by our DoS mechanism.
One glitch I can think of is at least the Qt client, where we use the medium of connected notes for the est. block count, which is used to decide if we are yet up to date and such stuff.
We never use this information for any important logic; it's only a display issue.
That said, some heuristics are probably possible to filter out meaningless values.
The received node heights are put through a median filter for this reason. One or even two large outliers will not affect the displayed value in any way.
There is no ddos potential at all, as the number is not and should not be used for anything critical.
Thanks :).