Description

In the generateCurveAddLiquidityProof function, if the value of rho happens to be null, then the nullifier is also set to zero:

const nullifier1 = param.note1.rho === 0n ? 0n : calcNullifier(param.note1.rho, fuzkPubKey);
const nullifier2 = param.note2.rho === 0n ? 0n : calcNullifier(param.note2.rho, fuzkPubKey);
const nullifier3 = param.note3.rho === 0n ? 0n : calcNullifier(param.note3.rho, fuzkPubKey);
const nullifier4 = param.note4.rho === 0n ? 0n : calcNullifier(param.note4.rho, fuzkPubKey);

A zero nullifier will not be verified properly by the verifier.

Impact

In the unlikely case where rho is zero, the nullifier is set to zero and will not verify, later making the corresponding note unspendable.

Recommendations

The nullifier should be computed such that the verifier is able to verify it correctly.

Remediation

This issue has been acknowledged by Singularity, and a fix was implemented in commit 2b464a25↗. The verification has been to change to check the amount value instead of rho.