It’s actually called a hashmap collision attack, fixed by randomizing your hash function at the program start. For example generating a key at program start that will be used with siphash.
The random seed can by extracted, exposed or calculated, and then siphash doesn't help you at all, it just makes everything 2x slower.
This is what all (non-vulnerable) programming languages do btw.
PS: saw your other post, interesting take.
https://news.ycombinator.com/item?id=12401920
I’ll venture a guess: a lot of practical attacks in the lab becomes completely impractical on a network.