CVE-2021-4070

Off-by-one Error in v2fly/v2ray-core

5.9 MediumFix available

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

Attack profile

How easy it is to exploit

Attack vector: Local
Complexity: Low
Privileges needed: None
User interaction: None

What an attacker can affect

Confidentiality: Low
Integrity: Low
Availability: Low

Exploit likelihood

0.86%Unchanged since Feb 24, 2022

What each source reports

CVE List Score used 5.9

Off-by-one Error in v2fly/v2ray-core

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

Record: CVE-2021-4070
CVSS 3.0: 5.9 MediumCVSS:3.0/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
Weakness: CWE-193
Updated: 2026-11-02

EUVDEUVD-2022-0809 5.9

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

Record: EUVD-2022-0809
CVSS 3.0: 5.9 MediumCVSS:3.0/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
Updated: 2026-11-03

GitHub AdvisoriesGHSA-4cxw-hq44-r344 9.1

Off-by-one Error in v2fly/v2ray-core

v2fly/v2ray-core prior to 4.44.0 is vulnerable to an off-by-one error. Indexing operations on arrays, slices, or strings should use an index at most one less than the length. If the index is checked for being less than or equal to the length (<=), instead of less than the length (<), the index could be out of bounds.

Record: GHSA-4cxw-hq44-r344
CVSS 3.1: 9.1 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
Weakness: CWE-193
Updated: 2026-11-02

NVD 9.1

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

Record: CVE-2021-4070
CVSS 3.1: 9.1 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
CVSS 3.0: 5.9 MediumCVSS:3.0/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
CVSS 2.0: 6.4 MediumAV:N/AC:L/Au:N/C:P/I:N/A:P
Weakness: CWE-193
Updated: 2026-11-02

OSV 9.1

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

Record: CVE-2021-4070
CVSS 3.1: 9.1 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
Updated: 2026-11-02

OSVDEBIAN-CVE-2021-4070 9.1

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

Record: DEBIAN-CVE-2021-4070
CVSS 3.1: 9.1 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
Updated: 2026-11-02

OSVGHSA-4cxw-hq44-r344 9.1

Off-by-one Error in v2fly/v2ray-core

Record: GHSA-4cxw-hq44-r344
CVSS 3.1: 9.1 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
Weakness: CWE-193
Updated: 2026-11-02

OSVUBUNTU-CVE-2021-4070 9.1

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

Record: UBUNTU-CVE-2021-4070
CVSS 3.1: 9.1 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
CVSS 3.0: 5.9 MediumCVSS:3.0/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
Updated: 2026-11-02

OSVGO-2022-0550 No score

Off-by-one Error in v2fly/v2ray-core in github.com/v2fly/v2ray-core

Off-by-one Error in v2fly/v2ray-core in github.com/v2fly/v2ray-core

Record: GO-2022-0550
Updated: 2026-11-02

Affected products

Affected packages

Affected packages
Package	Affected	Fixed
`github.com/v2fly/v2ray-core/v4` Go	before 4.44.0	4.44.0
`github.com/v2fly/v2ray-core` Go	before 4.44.0	4.44.0
`golang-v2ray-core` Debian:12	before 4.34.0-7	4.34.0-7
`golang-v2ray-core` Debian:13	before 4.34.0-7	4.34.0-7
`golang-v2ray-core` Debian:14	before 4.34.0-7	4.34.0-7
`github.com/v2fly/v2ray-core` Go	All versions	None known
`golang-v2ray-core` Ubuntu:22.04:LTS	All versions, plus listed versions 4.34.0-14.34.0-5	None known

History

History
Recorded	Changed	Sources
Nov 3, 2026	aliases	EUVD
Nov 2, 2026	first indexed	CVE List, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2021-4070 is a medium vulnerability (CVSS 5.9) in V2fly V2fly/v2ray-core, published February 23, 2022. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.86%, the 58th percentile. Fixed in github.com/v2fly/v2ray-core/v4 4.44.0.

Attack profile

How easy it is to exploit

What an attacker can affect

Exploit likelihood

What each source reports

Affected products

Affected packages

History

In short

References