WS-2023-0420

Date: August 19, 2025

gnark provides a gadget in the standard library to allow optimized checking of the bitwidth of the inputs. The gadget works by constructing a fixed lookup table containing all valid entries, partitioning the input and checking that all parts are inside the lookup table. The range checker gadget did not take into account that the highest partition may be less than the width limit, allowing the inputs to be up to 16 bits wider than checked. Range checking gadget is extensively used in field emulation. Users using any dependant gadget (ECDSA verification, proof recursion etc.) is impacted. We consider the impact of the vulnerability being low as the number of attacker-modifiable bits is significantly smaller compared to the bit-width of scalar field modulus and it won't be possible to construct inputs which would allow to overflow the scalar field.

Language: Go