How severe is CVE-2021-4234?

CVE-2021-4234 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-2021-4234 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (53rd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-4234?

CVE-2021-4234 affects Openvpn Openvpn Access Server. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-4234?

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-2021-4234 published?

CVE-2021-4234 was published on 2022-07-06 and last updated on 2026-06-17.

CVE-2021-4234

CVE-2021-4234 is a high-severity vulnerability in Openvpn Openvpn Access Server 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-406.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
EPSS exploit prediction: 1% (53rd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-406
Affected product: Openvpn Openvpn Access Server
Published: 2022-07-06
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2021-4234?: 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.
How severe is CVE-2021-4234?: CVE-2021-4234 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-2021-4234 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (53rd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-4234?: CVE-2021-4234 affects Openvpn Openvpn Access Server. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-4234?: 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-2021-4234 published?: CVE-2021-4234 was published on 2022-07-06 and last updated on 2026-06-17.

References

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

Affected products (1)

cpe:2.3:a:openvpn:openvpn_access_server:*:*:*:*:*:*:*:*

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