CVE-2021-39193Network attack vector

Invalid block metadata via missing gas-cost validation

Published Sep 3, 2021 · Updated Aug 4, 2024

Improper input validation in Frontier before commit 0b962f2 allows remote attackers to add ineffective transactions to block metadata. The pallet-ethereum validate_unsigned path accepts a transaction whose input-data gas cost exceeds its gas limit, then records its metadata even though EVM execution rejects it. No authentication or user interaction is required, but Substrate extrinsic-size limits bound storage growth and the transaction cannot change Ethereum or Substrate state.

CVSS severity5.3
Medium
EPSS probability1.19%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in Frontier before commit 0b962f2 allows remote attackers to add ineffective transactions to block metadata. The pallet-ethereum validate_unsigned path accepts a transaction whose input-data gas cost exceeds its gas limit, then records its metadata even though EVM execution rejects it. No authentication or user interaction is required, but Substrate extrinsic-size limits bound storage growth and the transaction cannot change Ethereum or Substrate state.

The record

CVE
CVE-2021-39193
Published
Sep 3, 2021
Updated
Aug 4, 2024
Vendor
Parity Technologies
Product
Frontier
Classifications
CWE-20, CWE-1284
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 3, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 0b962f218f0cdd796dadfe26c3f09e68f7861b26

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Parity Technologies · Frontierversion=< 0b962f218f0cdd796dadfe26c3f09e68f7861b26

Published CVSS scores

5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:P/A:N
5.3GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-20Improper Input Validation
CWE-1284Improper Validation of Specified Quantity in Input

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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