CVE-2021-42766Network attack vector

Consensus disruption via low-stake chain reorganization

Published Oct 20, 2021 · Updated Aug 4, 2024

Denial of service in Proof-of-Stake Ethereum through 2021-10-19 allows attackers to stall consensus via long-range chain reorganizations. The LMD-GHOST fork-choice process accepts strategically withheld blocks and attestations released at opportune times, allowing a low-stake validator to displace honest blocks and congest vote processing. The attacker must control validator stake but does not need to control network message propagation; the result is a protocol stall and potentially increased validator profit.

CVSS severity9.1
Critical
EPSS probability0.96%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Proof-of-Stake Ethereum through 2021-10-19 allows attackers to stall consensus via long-range chain reorganizations. The LMD-GHOST fork-choice process accepts strategically withheld blocks and attestations released at opportune times, allowing a low-stake validator to displace honest blocks and congest vote processing. The attacker must control validator stake but does not need to control network message propagation; the result is a protocol stall and potentially increased validator profit.

The record

CVE
CVE-2021-42766
Published
Oct 20, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
T1499.004
Attack vector
network
Privileges
Unavailable

Timeline

How it unfolded

  1. Oct 20, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesUnavailable in this record.

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

6.4NIST NVDAV:N/AC:L/Au:N/C:N/I:P/A:P
9.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

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
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1499.004Application or System Exploitation

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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