CVE-2025-58157: gnark affected by denial of service when computing scalar multiplication using fake-GLV algorithm

For optimizing the scalar multiplication algorithm in circuit for some curves, gnark uses fake-GLV algorithm in case the curve doesn’t support true-GLV. For this to work, we need to compute the scalar decomposition using the Half GCD method in gnark-crypto. However, for some of the inputs the algorithm didn’t converge quickly enough.

In case the prover accepts untrusted witness, it could lead to denial of service as the prover gets stuck in a very slowly converging loop.

Thanks to @feltroidprime for reporting the issue and proposing a fix.