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Try it yourself. Go to https://www.zalmos.com or https://www.proxfree.com on your Chrome or Firefox browser, and see if you can run a speedtest, or if you can run a standard DNS leak test. Is there some security issue in my browser implementation that is making the sites simply deny me a speedtest over an ssl proxy, or is some error occurring somewhere else that is making these tests fail? If anyone else can run the test and explain if it is working for them, i would really appreciate it, thank you.

Edit: forgot to add the websites for reference: beta.speedtest.net is the one for speedtest www.dnsleaktest.com is the one for checking dns leaks.

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These are not real proxies but just sites where you can enter a URL and which then tries to get the requested site for you and display it. And they try to rewrite links in the result so that future clicks stay within the proxy. This will fail in many cases if links are created dynamically using JavaScript which is probably the case here. Also, if the target site creates cookies within a HTTP response and queries these cookies within JavaScript it will not see the expected cookies because these got rewritten by the proxy.

In other words: these proxy sites modify the content in a way which might affect the functionality of the content. This might be a problem with some sites and might be no problem with other sites. A real proxy instead gets configured inside the browser or OS so that the browser itself knows that it should use this proxy for all requests. In this case no content rewriting is needed to keep using the proxy and thus breaking the functionality due to rewriting will not happen.

Please note also that using of such proxy sites creates new security problems: since all sites visited using such proxy site are loaded within the same domain (i.e. proxy.zalmos.com) the same origin policy will no longer restrict access between different sites, i.e. original cross-site activity will now be same-site activity. This makes it possible to read and modify the content of different sites which might result in stealing sensitive data or misuse of your identity. All these problems do not happen in case a real (browser configured) proxy is used.

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  • Thanks for shedding light on this. So could you help me understand for example why the IP is changed when i use the proxies, and i can watch videos on youtube via these proxies, and yet, as you say, the javascript in the case of actually doing a speedtest or dnsleaktest, fails to initialize? Its confusing to be, because it has masked my ip address, and dnsleaktest.com does show the proxies ip address, and yet this is only halfway, the actual test wont run! Thanks for your time Steffen.
    – Gigiisbae
    Commented Aug 31, 2017 at 5:21
  • I'm not saying that the JavaScript fails to initialize. I'm saying that the rewrite of links will fail in many cases if the links are created dynamically with JavaScript. If this is done depends on the target site.
    – Steffen Ullrich
    Commented Aug 31, 2017 at 5:24
  • Hmmm, i feel like you are saying something acutely insightful which i am missing. But yeah, so unlike a VPN or a proxy application (like putty perhaps?) a simple web-based proxy is not quite able to fully display and work on pages that would otherwise work perfectly without going through it.
    – Gigiisbae
    Commented Aug 31, 2017 at 5:49
  • @Gigiisbae: basically a web based proxy needs to modify the content so that everything keeps passing through the proxy. Such modifications are complex and will never be perfect and thus might inadvertently destroy functionality. Apart from that a web based proxy make everything cross domain to same domain and this way throws away in essential security feature of the browsers, the same origin policy which limits what one web site can do with another one inside the browser.
    – Steffen Ullrich
    Commented Aug 31, 2017 at 6:03
  • Ahh, its much clearer now, thanks for the stellar effort Steffen, your answer is really appreciated.
    – Gigiisbae
    Commented Aug 31, 2017 at 6:46

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