How severe is CVE-2021-42766?

CVE-2021-42766 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability high.

Is CVE-2021-42766 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (56th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-42766?

CVE-2021-42766 affects Proof-of-stake Ethereum Project Proof-of-stake Ethereum. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-42766?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2021-42766 published?

CVE-2021-42766 was published on 2021-10-20 and last updated on 2026-06-17.

CVE-2021-42766

CVE-2021-42766 is a critical-severity vulnerability in Proof-of-stake Ethereum Project Proof-of-stake Ethereum with a CVSS 3.x base score of 9.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low.

Key facts

Severity: Critical (CVSS 3.x base score 9.1)
CVSS v2: 6.4
EPSS exploit prediction: 1% (56th percentile)
Actively exploited: Not listed in CISA KEV
Affected product: Proof-of-stake Ethereum Project Proof-of-stake Ethereum
Published: 2021-10-20
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2021-42766?: 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.
How severe is CVE-2021-42766?: CVE-2021-42766 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability high.
Is CVE-2021-42766 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (56th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-42766?: CVE-2021-42766 affects Proof-of-stake Ethereum Project Proof-of-stake Ethereum. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-42766?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2021-42766 published?: CVE-2021-42766 was published on 2021-10-20 and last updated on 2026-06-17.

References

https://arxiv.org/abs/2110.10086

Affected products (1)

cpe:2.3:a:proof-of-stake_ethereum_project:proof-of-stake_ethereum:*:*:*:*:*:*:*:*

More vulnerabilities in Proof-of-stake Ethereum Project Proof-of-stake Ethereum

CVE-2021-42764 — Critical (CVSS 9.1): The Proof-of-Stake (PoS) Ethereum consensus protocol through 2021-10-19 allows an adversary to cause a denial of…
CVE-2021-42765 — High (CVSS 7.5): The Proof-of-Stake (PoS) Ethereum consensus protocol through 2021-10-19 allows an adversary to leverage network delay…

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