What is CVE-2021-4070?

CVE-2021-4070 is a critical-severity vulnerability in V2fly V2fly/v2ray-Core, classified under Off-by-one Error. CVSS score: 9.1/10. Published 2022-02-23.

How severe is CVE-2021-4070?

Critical severity. CVSS v3 base score is 9.1 out of 10.

Vulnerability in V2fly V2fly/v2ray-Core

CVE-2021-4070

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

Published 2022-02-23 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.1 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H.

EPSS exploit prediction

EPSS: 0.009 (56.8th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 57th percentile — 56.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.009 · newest: 0.009 · change: 0.000

Affected products

V2fly V2fly/v2ray-Core — versions unspecified
V2fly V2ray-Core

Weakness classification (CWE)

CWE-193 — Off-by-one Error

References

huntr.dev/bounties/8da19456-4d89-41ef-9781-a41efd6a1877 (Exploit, Patch, Third Party Advisory)
github.com/v2fly/v2ray-core/commit/c1af2bfd7aa59a4482aa7f6ec4b9208c1d350b5c (Patch, Third Party Advisory)

Frequently asked questions

What is CVE-2021-4070?: CVE-2021-4070 is a critical-severity vulnerability in V2fly V2fly/v2ray-Core, classified under Off-by-one Error. CVSS score: 9.1/10. Published 2022-02-23.
How severe is CVE-2021-4070?: Critical severity. CVSS v3 base score is 9.1 out of 10.