CVE-2023-28431 is a high-severity (CVSS 7.5) CWE-682 vulnerability in pallet-evm-precompile-modexp. No vendor fix is recorded yet; mitigation options are listed below.
Frontier's modexp precompile is slow for even modulus
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2023-28431.
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.
How urgent is this, really
CVE-2023-28431 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,636 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
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, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Remediation status
No patched version of pallet-evm-precompile-modexp has shipped for CVE-2023-28431 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 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2023-28431 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2023-28431. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2023-28431 in your dependencies?
O3 Security finds CVE-2023-28431 across crates.io dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.