# CVE-2021-41138: Validity check for signed Frontier-specific extrinsic not called in block execution

> Malicious validators can insert invalid transactions into blocks due to missing validation during execution, enabling chain ID replay attacks and spam.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 13 Oct 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-vj62-g63v-f8mf

## What is CVE-2021-41138?

CVE-2021-41138 is a medium-severity vulnerability in paritytech frontier, published on 13 Oct 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Frontier is Substrate's Ethereum compatibility layer. In the newly introduced signed Frontier-specific extrinsic for `pallet-ethereum`, a large part of transaction validation logic was only called in transaction pool validation, but not in block execution. Malicious validators can take advantage of this to put invalid transactions into a block. The attack is limited in that the signature is always validated, and the majority of the validation is done again in the subsequent `pallet-evm` execution logic. However, do note that a chain ID replay attack was possible. In addition, spamming attacks are of main concerns, while they are limited by Substrate block size limits and other factors. The issue is patched in commit `146bb48849e5393004be5c88beefe76fdf009aba`.

Weakness: CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2021-41138?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `pallet-ethereum` | crates.io | All versions to 3.0.0 | None |
| `pallet-ethereum` | crates.io | All versions to 3.0.0 | None |

Products: Parity Frontier.

## How do I fix CVE-2021-41138?

No fix has been published for CVE-2021-41138 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-41138 being exploited?

There is no known exploitation of CVE-2021-41138 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-2022-21685](https://insights.sbomify.com/CVE-2022-21685/): Integer underflow in Frontier (medium 6.5)
- [CVE-2022-39242](https://insights.sbomify.com/CVE-2022-39242/): Incorrect Calculation in Frontier leads to inflated Ethereum chain gas prices (medium 5.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-41138 and fix it if it is affected.

What it is: CVE-2021-41138 is a medium-severity vulnerability in paritytech frontier, published on 13 Oct 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-41138 in the wild and no public exploit code.

Affected packages and fixed versions:
- pallet-ethereum (crates.io): affected all versions up to 3.0.0; no fix listed
- pallet-ethereum (crates.io): affected all versions up to 3.0.0; 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-2021-41138/ (Markdown: https://insights.sbomify.com/CVE-2021-41138/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-41138
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-41138
- OSV: https://osv.dev/vulnerability/CVE-2021-41138

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-41138/
Summaries are generated and may contain mistakes; the official description above is the record.