OpenVPN up to 2.7.6 NRPT buffer overflow

Summaryinfo

A vulnerability marked as very critical has been reported in OpenVPN up to 2.7.6. The affected element is an unknown function of the component NRPT Handler. The manipulation leads to buffer overflow. This vulnerability is referenced as CVE-2026-78221. The attack can only be performed from a local environment. No exploit is available.

Detailsinfo

A vulnerability was found in OpenVPN up to 2.7.6 and classified as very critical. This issue affects an unknown code of the component NRPT Handler. The manipulation with an unknown input leads to a buffer overflow vulnerability. Using CWE to declare the problem leads to CWE-120. The product copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer, leading to a buffer overflow. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

An incorrect buffer size calculation in the Windows Interactive Service in OpenVPN 2.7_alpha1 through 2.7.6 allows local authenticated users to cause memory corruption or disclose sensitive information via crafted NRPT inputs.

It is possible to read the advisory at community.openvpn.net. The identification of this vulnerability is CVE-2026-78221 since 08/26/2026. The exploitation is known to be easy. Attacking locally is a requirement. It demands that the victim is doing some kind of user interaction. The technical details are unknown and an exploit is not publicly available. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 09/07/2026).

The vulnerability scanner Nessus provides a plugin with the ID 343061 (Linux Distros Unpatched Vulnerability : CVE-2026-78221), which helps to determine the existence of the flaw in a target environment.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

The vulnerability is also documented in the databases at Tenable (343061) and EUVD (EUVD-2026-72276). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Productinfo

Type

• Network Encryption Software

Name

• OpenVPN

Version

• 2.7.0
• 2.7.1
• 2.7.2
• 2.7.3
• 2.7.4
• 2.7.5
• 2.7.6

License

• open-source

CPE 2.3info

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CPE 2.2info

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Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

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