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

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-10-13 · updated 2026-06-17
Weakness: CWE-20

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`.

Affected products

paritytech frontier: from 2021-09-30 before 2021-10-13 — fixed in 2021-10-13

How to fix

Upgrade to a fixed version: paritytech frontier 2021-10-13. Check the vendor advisory for mitigations.

References

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