Mohamed Ali Kaafar, principal researcher in online privacy and security at Australia’s CSIRO's Data61, co-authored the paper with researchers from UNSW, ICSI, and UC Berkeley. Researchers tested 238 Android apps from Google Play and revealed that many free VPNs are thinly disguised malware, adware, data stealers and that users don’t really know or care – the lure of a free VPN is enough to attract users.
It found that most apps simply call Android’s built-in BIND_VPN_SERVICE that allows it to intercept and take full control of a user’s traffic. Malicious app developers can abuse the call to harvest users’ personal information.
The paper is here – below is a summary of its findings.
- 75% of such VPN apps use third-party tracking libraries (they know what websites you visit or search terms used etc.).
- 82% request permissions to access sensitive resources including user accounts, text messages, contacts, calendar, emails and system logs – they are VPN honeypots to trap user data.
- 38% contain malware.
- 18% do not use the terminating VPN server entity.
- 16% forward traffic through other participating users in a peer-forwarding fashion rather than using machines hosted in the cloud. This forwarding model raises trust, security, and privacy concerns.
- 4% use the VPN permissions to implement localhost proxies to intercept and inspect user traffic locally.
- 18% implement unencrypted tunnelling protocols despite promising online anonymity and security.
- 84% and 66% respectively do not tunnel IPv6 and DNS traffic through the tunnel interface opening users up to man-in-the-middle Wi-Fi attacks.
- Four compromise users’ root-store and actively perform in-flight TLS interception. Some of these apps claim traffic acceleration services and selectively intercept traffic to specific online services like social networks, banking, e-commerce sites, email and IM services and analytics services.
The report casts serious doubt on the intent and validity of most free VPN apps as nothing more than a claimed panacea – it says that from 2011 to 2013 free VPN apps skyrocketed tenfold. The apps are mostly identified as VPNs but can also be called traffic optimisers, communications tools, traffic filters or even Tor clients. Many offer in-app purchases (to premium versions or third party apps) a feature of most freemium apps.
The report concludes:
The increasing number of popular VPN apps available on Google Play and the apparent lack of user awareness of the security and privacy risks associated with the VPN permission indicate the need to analyse in depth this unexplored type of mobile app. The average mobile user rates VPN apps positively even when they have malware presence. Only a handful of users has raised any type of security and privacy concern in their reviews.
Researchers contacted and shared findings with the app developers:
- Apps requesting sensitive permissions, apps that are negatively reviewed by users, and the ones with embedded third-party tracking libraries.
- Apps possibly containing malware in their APKs.
The developers' poor responses are in Section 5.5 of the report. Of the 238 free apps none appeared to receive a completely clean bill of health.