GHSA-498w-5j49-vqjg
MEDIUMgnark unsoundness in variable comparison / non-unique binary decomposition
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
github.com/consensys/gnarkReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
Impact
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.
Internally, the comparison methods frontend.API.Cmp and frontend.API.IsLess used binary decomposition and checked the bitwise differences. This allows a malicious prover to construct a valid proof for a statement a < b even if a > b.
The issue impacts all users using API.Cmp or API.IsLess methods. Additionally, it impacts the users using bits.ToBinary or API.ToBinary methods if full-width decomposition is requested (the default behaviour if no options are given).
The issues does not impact comparison methods in field emulation (package std/math/emulated) and dedicated comparison package (std/math/cmp).
Patches
Fix has been implemented in pull request #835 and merged in commit 59a4087261a6c73f13e80d695c17b398c3d0934f to master branch. The release v0.9.0 and onwards include the fix.
The fix added additional comparison of the decomposed bit-vector to the modulus of the in-circuit values.
Workarounds
Upgrading to version v0.9.0 should fix the issue without needing to change the calls to value comparison methods.
Alternatively, users can use the std/math/cmp gadget, which additionally allows to bound the number of bits being compared, making the comparisons more efficient if the bound on the absolute difference of the values is known.
References
- https://github.com/Consensys/gnark/pull/835
- https://github.com/zkopru-network/zkopru/issues/116
- https://github.com/iden3/circomlib/pull/48
Acknowledgement
The vulnerability was reported by Marcin Kostrzewa @ Reilabs.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/consensys/gnark | all versions | 0.9.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/consensys/gnark. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update github.com/consensys/gnark to 0.9.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-498w-5j49-vqjg is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-498w-5j49-vqjg is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-498w-5j49-vqjg. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-498w-5j49-vqjg in your dependencies?
O3 detects GHSA-498w-5j49-vqjg across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.