Headline
GHSA-9fvj-xqr2-xwg8: gnark affected by denial of service when computing scalar multiplication using fake-GLV algorithm
Impact
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.
Patches
The issue has been patched in gnark-crypto commit https://github.com/Consensys/gnark-crypto/commit/56600883e0e9f9b159e9c7000b94e76185ec3d0d. The dependency update is implemented in gnark commit https://github.com/Consensys/gnark/commit/68be6cede36e387ab760725beabd3c96cc94e6dc.
Workarounds
This update doesn’t require recompiling the circuits as the issue is in the hint function. The users can update the gnark-crypto dependency to the fixed version.
References
- See bug report https://github.com/Consensys/gnark/issues/1483
- Fake GLV description https://ethresear.ch/t/fake-glv-you-dont-need-an-efficient-endomorphism-to-implement-glv-like-scalar-multiplication-in-snark-circuits/20394
Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.