Frontier's modexp precompile is slow for even modulus

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS

• CVE-2023-28431: 0.87% estimated exploitation activity in the next 30 days; percentile 58.96 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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…

Published by the source

21 Mar 2023, 22:31 UTC

Last modified by the source

24 Oct 2024, 21:21 UTC

Source last checked

26 Oct 2026, 15:38 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-fcmm-54jp-7vf6

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2023-28431

Advisory: Frontier's modexp precompile is slow for even modulus
IDs: CVE-2023-28431, GHSA-fcmm-54jp-7vf6
Record: https://patchnext.com/advisories/cve-2023-28431 (revision 1, source checked 26 Oct 2026, 15:38 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor response not established. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io pallet-evm-precompile-modexp: affected <= 1.0.0

## Suggested inspection (read-only)
- crates.io pallet-evm-precompile-modexp: check the installed version with your package manager.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on pallet-evm-precompile-modexp.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-fcmm-54jp-7vf6 (GitHub-reviewed advisory GHSA-fcmm-54jp-7vf6 lists affected ranges: crates.io pallet-evm-precompile-modexp >=0 <=1.0.0)

Commands are suggestions: review each one before running it.