Once you understand the packet you want to match on, you can convert this
into a Deny Rule-Action, tuning the Depth and Log-Mask to optimized the
filter performance.
FWIW, if this were my problem, I would use an observe rule to blacklist
the source.
Massimo, is the really the logged URL:
/referenze.html/.../referenze.html/
It does not look valid to me. If you edited it, don't do that in the
future. I am only willing to try so hard to help you.