A serious vulnerability has been found in early versions of OpenVPN (specifically from 2.7_alpha1 to 2.7_beta1) that impacts Linux, macOS, and other POSIX-based clients. A malicious VPN server could exploit this flaw to execute arbitrary commands on a connecting client device simply by manipulating DNS or DHCP options passed during the VPN session.
How It Works
- The vulnerability resides in insufficient sanitisation of the –dns and –dhcp-option arguments that client software receives from a server.
- When a client connects to a malicious or compromised VPN server, these arguments are passed to the –dns-updown hook script without proper sanitisation, allowing injection of shell meta-characters or commands.
- Because many organisations use VPN clients to connect remote endpoints or branch offices, this flaw lets an adversary pivot from the VPN server into client machines with high privileges.
- The vulnerability is identified as CVE‑2025‑10680 with a CVSS score of 8.-indicating high severity.
- While Windows is less exposed (because this particular script logic is more prevalent on Unix‐like clients), any system that uses the vulnerable client build and connects to untrusted servers should be considered at risk.
Why This Should Matter to You
- The attack vector doesn’t require user interaction beyond connection to a compromised or malicious VPN server. Once connected, the client is at risk.
- Many enterprises rely on VPNs to extend secure access to remote employees, cloud networks, or partner systems-making this a broad-impact issue.
- If a client machine is subverted, an attacker could exfiltrate data, drop malware, move laterally into the internal network, or take control of connected resources.
- Given the plausible use of third-party VPN servers, contractor endpoints, or even public VPN servers in supply-chain or vendor access workflows, the attack surface is large.
- The issue underlines that not just servers, but client endpoint software and the trust model of remote access tools must be treated as part of the threat surface.
What Organisations Should Do Immediately
- Pause deployment of 2.7-alpha/beta clients – avoid using the affected builds (2.7_alpha1 to 2.7_beta1). Use the last stable version or apply the fix when available.
- Upgrade clients – update to a version of OpenVPN that addresses CVE-2025-10680 or configure clients to disable the –dns-updown hook where practical.
- Restrict connections to trusted servers only – enforce strict VPN server access policies, especially for remote or third-party endpoints.
- Harden client endpoint security – enforce least privilege on client machines, use endpoint detection & response (EDR) tools, monitor for script invocation or abnormal processes spawned by VPN clients.
- Isolate remote access sessions – segment VPN clients from sensitive internal systems unless absolutely needed; use zero-trust access patterns where possible.
- Monitor for signs of exploitation – flagged scripts, unexpected network connections post-VPN connection, script logs showing meta-character injection.
- Train end-users and support staff – ensure users understand only trusted VPN servers should be used and that connecting to unknown servers carries risks.
Conclusion
The discovery of a script-injection flaw in OpenVPN client builds is a clear reminder that remote access tools must be held to the same security scrutiny as servers and network devices. A compromised VPN client can be the gateway for attackers into corporate systems. Organisations should act immediately: update clients, restrict server access, monitor endpoints, and treat VPN software as part of the core attack surface—not just a connectivity utility.
About COE Security
COE Security partners with organisations in financial services, healthcare, retail, manufacturing, and government to secure AI-powered systems and ensure compliance. Our offerings include:
- AI-enhanced threat detection and real-time monitoring
- Data governance aligned with GDPR, HIPAA, and PCI DSS
- Secure model validation to guard against adversarial attacks
- Customised training to embed AI security best practices
- Penetration Testing (Mobile, Web, AI, Product, IoT, Network & Cloud)
- Secure Software Development Consulting (SSDLC)
- Customised CyberSecurity Services
In light of remote access risks like the OpenVPN client vulnerability, we also provide VPN/remote access risk assessments, endpoint compromise readiness, client-software hardening consulting, and remote-session monitoring frameworks.
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