gnark vulnerable to unsoundness in variable comparison/non-unique binary decomposition

Vulnerability Description

gnark is a zk-SNARK library that offers a high-level API to design circuits. Prior to version 0.9.0, for some in-circuit values, it is possible to construct two valid decomposition to bits. In addition to the canonical decomposition of `a`, for small values there exists a second decomposition for `a+r` (where `r` is the modulus the values are being reduced by). The second decomposition was possible due to overflowing the field where the values are defined. Upgrading to version 0.9.0 should fix the issue without needing to change the calls to value comparison methods.

References

• https://github.com/Consensys/gnark/security/advisories/GHSA-498w-5j49-vqjg
• https://github.com/zkopru-network/zkopru/issues/116
• https://github.com/Consensys/gnark/commit/59a4087261a6c73f13e80d695c17b398c3d0934f