CVE-2021-42766: The Proof-of-Stake (PoS) Ethereum consensus protocol through 2021-10-19 allows an adversary to cause a denial

Q: How do I fix CVE-2021-42766?

proof-of-stake ethereum: upgrade to newer than 2021-10-19. Exact commands for each OS are on this page.

Q: Is CVE-2021-42766 being exploited?

CVE-2021-42766 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2021-42766 affect?

CVE-2021-42766 affects proof-of-stake ethereum. Severity is critical (CVSS 9.1). 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 me

Q: How urgent is CVE-2021-42766?

Priority 52/100. Critical severity; Remotely exploitable, no login, no user action

This month

CRITICAL 9.1REMOTEUPGRADE

CVE-2021-42766 is a critical-severity flaw (CVSS 9.1) affecting proof-of-stake ethereum. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

Critical severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.1 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.0% (top 38%)
CISA exploited list	No
Published	2021-10-20
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: proof-of-stake ethereum project

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-10-20 20:15 UTCPublished CVE record published
2026-06-17 04:10 UTCUpdated Record last modified

proof-of-stake ethereum project proof-of-stake ethereum UPGRADE

Affected: <= 2021-10-19

Fixed in: newer than 2021-10-19

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy proof-of-stake-ethereum || rpm -q proof-of-stake-ethereum || proof-of-stake-ethereum --version

2. UPGRADE to newer than 2021-10-19 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade proof-of-stake-ethereum

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade proof-of-stake-ethereum

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-42766?

proof-of-stake ethereum: upgrade to newer than 2021-10-19. Exact commands for each OS are on this page.

Is CVE-2021-42766 being exploited?

CVE-2021-42766 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-42766 affect?

CVE-2021-42766 affects proof-of-stake ethereum. Severity is critical (CVSS 9.1). 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 me

How urgent is CVE-2021-42766?

Priority 52/100. Critical severity; Remotely exploitable, no login, no user action

Related CVEs

CVE-2021-42765 HIGH 7.5 UPGRADE The Proof-of-Stake (PoS) Ethereum consensus protocol through 2021-10-19 allows an adversary to leverage networ
CVE-2021-42764 CRITICAL 9.1 UPGRADE The Proof-of-Stake (PoS) Ethereum consensus protocol through 2021-10-19 allows an adversary to cause a denial

References

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