Plonky2 is a SNARK implementation based on techniques from PLONK and FRI. Lookup tables, whose length is not divisible by 26 = floor(num_routed_wires / 3) always include the 0 -> 0 input-output pair. Thus a malicious prover can always prove that f(0) = 0 for any lookup table f (unless its length happens to be divisible by 26). The cause of problem is that the LookupTableGate-s are padded with zeros. A workaround from the user side is to extend the table (by repeating some entries) so that its length becomes divisible by 26. This vulnerability is fixed in 1.0.1.

Soundness issue with Plonky2 look up tables