How severe is CVE-2021-4070?

CVE-2021-4070 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 high, integrity none, and availability high.

Is CVE-2021-4070 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (54th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-4070?

CVE-2021-4070 affects V2fly V2ray-core. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-4070?

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-2021-4070 published?

CVE-2021-4070 was published on 2022-02-23 and last updated on 2026-06-17.

CVE-2021-4070

CVE-2021-4070 is a critical-severity vulnerability in V2fly V2ray-core 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. The underlying weakness is classified as CWE-193.

Key facts

Severity: Critical (CVSS 3.x base score 9.1)
CVSS v2: 6.4
EPSS exploit prediction: 1% (54th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-193
Affected product: V2fly V2ray-core
Published: 2022-02-23
Last modified: 2026-06-17

Description

Off-by-one Error in GitHub repository v2fly/v2ray-core prior to 4.44.0.

Frequently asked questions

What is CVE-2021-4070?: Off-by-one Error in GitHub repository v2fly/v2ray-core prior to 4.44.0.
How severe is CVE-2021-4070?: CVE-2021-4070 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 high, integrity none, and availability high.
Is CVE-2021-4070 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (54th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-4070?: CVE-2021-4070 affects V2fly V2ray-core. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-4070?: 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-2021-4070 published?: CVE-2021-4070 was published on 2022-02-23 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:v2fly:v2ray-core:*:*:*:*:*:*:*:*

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