CVE-2021-4234

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.9% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2022-07-06 · updated 2026-06-17
Weakness: CWE-406

Description

OpenVPN Access Server 2.10 and prior versions are susceptible to resending multiple packets in a response to a reset packet sent from the client which the client again does not respond to, resulting in a limited amplification attack.

Affected products

OpenVPN Access Server: before 2.11.0 — fixed in 2.11.0

How to fix

Upgrade to a fixed version: OpenVPN Access Server 2.11.0. Check the vendor advisory for mitigations.

References

https://openvpn.net/vpn-server-resources/release-notes/#openvpn-access-server-2-11-0
https://openvpn.net/vpn-server-resources/release-notes/#openvpn-access-server-2-11-0

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