CVE-2021-42766

Name: CVE-2021-42766
Creator: NVD / NIST
Published: 2021-10-20T20:15:07.517+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 9.1/10EPSS 0.93%

Last modified Jun 17, 2026

CVE-2021-42766 is a critical-severity vulnerability rated 9.1/10 on the CVSS scale. The Proof-of-Stake (PoS) Ethereum consensus protocol through 2021-10-19 allows an adversary to cause a denial of service (long-range consensus chain reorganizations), even when this adversary has little stake and cannot influence network message propagation. This can cause a protocol stall, or an increase in the profits of individual validators.. EPSS estimates a 0.93% chance of exploitation in the next 30 days.

Description

The Proof-of-Stake (PoS) Ethereum consensus protocol through 2021-10-19 allows an adversary to cause a denial of service (long-range consensus chain reorganizations), even when this adversary has little stake and cannot influence network message propagation. This can cause a protocol stall, or an increase in the profits of individual validators.

Metrics

CVSS 3.1

9.1/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

EPSS Probability

0.93%

56.0th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Vendor	Product	Versions
Proof-Of-Stake Ethereum Project	Proof-Of-Stake Ethereum	<= 2021-10-19

References

https://arxiv.org/abs/2110.10086Third Party Advisory
https://arxiv.org/abs/2110.10086Third Party Advisory

Timeline

Published: Oct 20, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-42766?

How severe is CVE-2021-42766?

CVE-2021-42766 has a CVSS score of 9.1/10 (CRITICAL severity). The EPSS model estimates a 0.93% probability of exploitation in the next 30 days.

How do I fix CVE-2021-42766?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-42766?

Run a free Strix scan to check your systems for this vulnerability.

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Source: NVD / NIST