How severe is CVE-2018-20421?

CVE-2018-20421 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2018-20421 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (70th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2018-20421?

CVE-2018-20421 affects Ethereum Go Ethereum. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2018-20421?

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

When was CVE-2018-20421 published?

CVE-2018-20421 was published on 2018-12-24 and last updated on 2026-06-17.

CVE-2018-20421

CVE-2018-20421 is a high-severity vulnerability in Ethereum Go Ethereum with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-770.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
EPSS exploit prediction: 1% (70th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-770
Affected product: Ethereum Go Ethereum
Published: 2018-12-24
Last modified: 2026-06-17

Description

Go Ethereum (aka geth) 1.8.19 allows attackers to cause a denial of service (memory consumption) by rewriting the length of a dynamic array in memory, and then writing data to a single memory location with a large index number, as demonstrated by use of "assembly { mstore }" followed by a "c[0xC800000] = 0xFF" assignment.

Frequently asked questions

What is CVE-2018-20421?: Go Ethereum (aka geth) 1.8.19 allows attackers to cause a denial of service (memory consumption) by rewriting the length of a dynamic array in memory, and then writing data to a single memory location with a large index number, as demonstrated by use of "assembly { mstore }" followed by a "c[0xC800000] = 0xFF" assignment.
How severe is CVE-2018-20421?: CVE-2018-20421 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2018-20421 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (70th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2018-20421?: CVE-2018-20421 affects Ethereum Go Ethereum. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2018-20421?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2018-20421 published?: CVE-2018-20421 was published on 2018-12-24 and last updated on 2026-06-17.

References

https://github.com/ethereum/go-ethereum/issues/18289

Affected products (1)

cpe:2.3:a:ethereum:go_ethereum:1.8.19:*:*:*:*:*:*:*

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