# CVE-2022-21685: Integer underflow in Frontier

> An integer underflow in the Frontier MODEXP precompile can cause node crashes in debug builds, requiring a patch for affected Substrate nodes.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 14 Jan 2022
- **Updated:** 23 Apr 2025
- **Also known as:** GHSA-cjg2-2fjg-fph4

## What is CVE-2022-21685?

CVE-2022-21685 is a medium-severity vulnerability in paritytech frontier, published on 14 Jan 2022. Any signed-in user can exploit it over the network, with no action from the victim.

### Official 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.

Weakness: CWE-191 (Integer Underflow (Wrap or Wraparound))

## Which versions are affected by CVE-2022-21685?

2 open source packages ship an affected version, including pallet-evm-precompile-modexp. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `pallet-evm-precompile-modexp` | crates.io | All versions to 1.0.0 | None |
| `pallet-evm-precompile-modexp` | crates.io | All versions to 1.0.0 | None |

Products: Parity Frontier.

## How do I fix CVE-2022-21685?

No fix has been published for CVE-2022-21685 yet. Limit exposure of the affected software until one is available.

## Is CVE-2022-21685 being exploited?

There is no known exploitation of CVE-2022-21685 in the wild and no public exploit code.

## Other vulnerabilities in paritytech frontier

- [CVE-2023-45130](https://insights.sbomify.com/CVE-2023-45130/): Frontier opcode SUICIDE touches too many storage values on large contracts (high 7.5)
- [CVE-2023-28431](https://insights.sbomify.com/CVE-2023-28431/): Frontier's modexp precompile is slow for even modulus (high 7.5)
- [CVE-2022-36008](https://insights.sbomify.com/CVE-2022-36008/): Message length overflow in frontier (high 7.1)
- [CVE-2022-39242](https://insights.sbomify.com/CVE-2022-39242/): Incorrect Calculation in Frontier leads to inflated Ethereum chain gas prices (medium 5.3)
- [CVE-2022-31111](https://insights.sbomify.com/CVE-2022-31111/): Discrepency in transfer value and actual value due to incorrect truncation in Frontier (medium 5.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2022-21685 and fix it if it is affected.

What it is: CVE-2022-21685 is a medium-severity vulnerability in paritytech frontier, published on 14 Jan 2022. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2022-21685 in the wild and no public exploit code.

Affected packages and fixed versions:
- pallet-evm-precompile-modexp (crates.io): affected all versions up to 1.0.0; no fix listed
- pallet-evm-precompile-modexp (crates.io): affected all versions up to 1.0.0; no fix listed

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2022-21685/ (Markdown: https://insights.sbomify.com/CVE-2022-21685/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2022-21685
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2022-21685
- OSV: https://osv.dev/vulnerability/CVE-2022-21685

---
From sbomify Insights: https://insights.sbomify.com/CVE-2022-21685/
Summaries are generated and may contain mistakes; the official description above is the record.