ExpressVPN has updated its Windows app to patch a vulnerability which could have exposed a user’s IP address to observers.
As one of the best VPNs, ExpressVPN is very secure but mistakes can happen. The provider said in a blog post that code meant for internal testing “mistakenly made it into production builds.”
Only users in specific conditions were affected, but the bug meant traffic wasn’t being routed through the VPN tunnel as expected – however encryption was not impacted.
ExpressVPN acted quickly to fix the vulnerability and is recommending all its Windows VPN users upgrade to the latest version of the app.
The code meant for internal testing found its way into production build versions 12.97 to 12.101.0.2-beta.
It was reported to ExpressVPN in April 2025 by security researcher Adam-X through the provider’s bug bounty program – where security researchers can earn cash rewards for reporting vulnerabilities and flaws.
ExpressVPN said its team confirmed and triaged the report within hours.
The vulnerability centred around Remote Desktop Protocol (RDP). According to ExpressVPN there was only a risk when an RDP connection was in use or when other TCP traffic was routed over port 3389.
ExpressVPN said “if a user established a connection using RDP, that traffic could bypass the VPN tunnel.”
“This did not affect encryption, but it meant that traffic from RDP connections wasn’t routed through ExpressVPN as expected.”
It added that observers such as internet service providers could see that a user was connected to ExpressVPN and that they were using RDP to access remote servers – information that would ordinarily be protected.
RDP is most commonly used in enterprise environments, and therefore most users were unaffected. However ExpressVPN said it considers “any risk to privacy unacceptable.”
A fix was released five days later in version 12.101.0.45. The researcher confirmed the issue was resolved and ExpressVPN closed the report at the end of June.
How severe could this have been?
ExpressVPN analysed the issues and believed “the likelihood of real-world exploitation was extremely low.”
Given the fact a majority of ExpressVPN users are individuals as opposed to enterprise customers, the provider said “the number of affected users is likely small.”
For a hacker to exploit the vulnerability, they would’ve needed to be aware of the bug and find a way to route traffic over port 3389. This could’ve been done by tricking a user into clicking on a malicious link or compromising a popular website to launch a drive-by attack – all while the user was connected to the VPN.
As demonstrated by Adam-X, a user’s real IP address could’ve been revealed. But browsing activity couldn’t have been seen and encryption was not compromised.
ExpressVPN said it was grateful to its community for notifying it of potential issues and suggesting improvements. The provider will strengthen its internal safeguards to ensure this doesn’t happen again.
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