GHSA-fcmm-54jp-7vf6
HIGHFrontier's modexp precompile is slow for even modulus
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
pallet-evm-precompile-modexpReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.
Description
Impact
Frontier's modexp precompile uses num-bigint crate under the hood. In the implementation, the cases for modulus being even and modulus being odd are treated separately. Odd modulus uses the fast Montgomery multiplication, and even modulus uses the slow plain power algorithm. This gas cost discrepancy was not accounted for in the modexp precompile, leading to possible denial of service attacks.
Patches
No fixes for num-bigint is currently available, and thus this advisory will be first fixed in the short term by raising the gas costs for even modulus, and in the long term fixing it in num-bigint or switching to another modexp implementation.
The short-term fix for Frontier is deployed at PR 1017.
The recommendations are as follows:
- If you anticipate malicious validators, it's recommended to issue an emergency runtime upgrade as soon as possible.
- If you do not anticipate malicious validators, it's recommended to issue a normal runtime upgrade, as Substrate has builtin timeout protection when validators are building blocks.
Workarounds
None.
References
A similar issue was presented in Geth's implementation and the fix can be found here.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | pallet-evm-precompile-modexp | all versions | No fix |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for pallet-evm-precompile-modexp. 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.
Remediation status
No patched version of pallet-evm-precompile-modexp has shipped for GHSA-fcmm-54jp-7vf6 yet. Where your build allows, override or pin the dependency away from the vulnerable range, and apply any maintainer-recommended mitigation.
Mitigate without a patch
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-fcmm-54jp-7vf6 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-fcmm-54jp-7vf6. 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-fcmm-54jp-7vf6 in your dependencies?
O3 detects GHSA-fcmm-54jp-7vf6 across crates.io dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.