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Redazione RHC : 22 June 2025 18:54
A critical vulnerability has been discovered in the OpenVPN data channel offload driver for Windows, which can be exploited by local attackers to crash systems. The bug, classified as CVE-2025-50054, is a buffer overflow that affects 1.3.0 and earlier versions of the ovpn-dco-win driver, as well as OpenVPN versions up to 2.5.8, where that driver was used as the default virtual network adapter.
“When using ovpn-dco-win, the OpenVPN software does not send data traffic back and forth between user and kernel space for encryption, decryption, and routing, but payload operations occur in the Windows kernel,” according to documentation released by OpenVPN .
According to the researchers, an unprivileged user process can send control messages with oversized buffers to the kernel driver, resulting in an overflow condition that leads to a crash. The issue highlights the risks of memory management in low-level drivers, which can often be exploited without elevated privileges.
This may allow attackers to cause a denial of service for affected systems, as attackers could repeatedly crash Windows computers running vulnerable OpenVPN installations. If exploited, this vulnerability impacts system availability without compromising data confidentiality or integrity.
The OpenVPN community project team responded by releasing OpenVPN 2.7_alpha2, which includes a fix for CVE-2025-50054, among several other improvements. Although this is an alpha release not intended for production use, the security fix addresses the critical vulnerability that affects widely distributed stable releases.
The ovpn-dco-win driver, which stands for “OpenVPN Data Channel Offload for Windows”, represents a significant architectural improvement over previous driver implementations. Unlike traditional approaches, the DCO driver processes VPN traffic directly in the Windows kernel rather than sending data back and forth between the user and kernel space, resulting in substantial performance improvements.
The driver is developed using modern frameworks, including WDF and NetAdapterCx, making it easier to maintain than existing NDIS miniport drivers. With version 2.7_alpha2, OpenVPN has officially removed support for the wintun driver, making win-dco the default, while tap-windows6 serves as a fallback for use cases not covered by win-dco.
Security experts recommend that users of affected builds upgrade to the patched versions as soon as stable releases are available. Until then, administrators should consider implementing mitigations to limit local access to the OpenVPN driver interfaces.
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