Why is Cloudfront loading scripts in my web app? (I don't use it)

Question

I manage a secured PHP/MySQL web app with extensive jQuery use. Today, a strange error popped up in our app\'s logs:

JS Error: Error loading script:
https://d15g         


        

Answer 1

Disclaimer: I'm not a security analyst/expert, your issue simply sparked my interest ;)

Warning: While I share the initial conclusion that the code itself is probably harmless, the underlying technology can most certainly be (ab)used for malicious intents as well, so please take care when investigating this yourself.

Analysis

You already found the relevant evidence yourself - searching further I found another pastebin drop, which is more readable, so I'm using this for the explanation (though at first sight the other one would allow this as well after formatting).

The snippet features JavaScript fragments with the following major functionality:

• Line 13 initializes the variable _GPL with all sorts of items for later use, e.g. various constants`, helper functions, browser compatibility stuff and actual payloads, for example:

  • Line20 defines an empty basdeCDN, line 21 defines a fCDN, which happens to be the one in question (d15gt9gwxw5wu0.cloudfront.net)

  • line 261 defines a function removeScripts(), which in turn uses findScript()from line 266, further accompanied by insertJS() on line 277 - their respective intend is obvious

  • line 270 defines function loadDomainRules(), which seems to be the one generating the URL you have found in your logs - see appendix below for the code snippet

    • Deduction: Even without further evidence gathered below, the naming and functionality strongly hints on r.js being a JavaScript file serving custom JavaScript specifically assembled/generated for the domain at hand
      
      

  • line 100 defines a function loadGeo(), which references some kind of an ad server indeed (ads2srv.com) - see appendix below for the code snippet

  • line 368 finally defines a function i(), which provides the most definite clues regarding the likely origin of all this, namely the notion of some Yontoo Client and Yontoo API - see appendix below for the code snippet

Corollary

What's it all about?

The extracted clues Yontoo Client and Yontoo API easily lead to Yontoo, an Application Platform that allows you to control the websites you visit everyday, i.e. it sounds like a commercialized version of Userscripts.org, see What is a Yontoo App?:

Yontoo is a browser add-on that customizes and enhances the underlying website

Where Can I Use It?

Yontoo works on any site on the Web, although the functionality comes from separate applications called Yontoo Apps which provide specific functionalities depending on what site you are on.

[emphasis mine]

Now, looking at the current listings in their App Market easily demonstrates, why this might be used for questionable nontransparent advertizing as well for example, all the trust signs and seals in their footer notwithstanding.

How did it end up in your logs?

Another quote provides more insight into the functionality and how it might have yielded the issue you've encountered:

Yontoo [...] is a browser add- on that creates virtual layers that can be edited to create the appearance of having made changes to the underlying website. [...] If you see a need for an application or tool over a website, then you are free to create!

So somebody apparently has visited your site and created some custom domain rules for it by means of the Yontoo client (if it actually allows this for end users) or one of the available apps (the snippet used for analysis references the Drop Down Deals app in line 379 for example), which triggered the creation of d15gt9gwxw5wu0.cloudfront.net/js/_MY_WEB_APP_DOMAIN_/r.js to store these rules for reuse on next site visit in turn.

Due to some security flaw somewhere (see conclusion below) this URL or a respective JavaScript snippet must have been injected into JavaScript code of your application (e.g. by means of Cross-site scripting (XSS) indeed), and triggered the log entry error at some point in turn.

Conclusion

As mentioned upfront already, I share the initial conclusion that the code itself is probably harmless, although the underlying technology can most certainly be (ab)used for malicious intents as well due to its very nature of mocking with client side JavaScript, i.e. a user allows code from a 3rd party service to interact with sites (and especially data) he uses and trusts every day - your case is the apparent evidence for something gone wrong already in this regard.

I haven't investigated the security architecture (if any) of Yontoo, but wasn't able to find any information regarding this important topic immediately on their website either (e.g. in their Support section), which is pretty much unacceptable for a technology like this IMHO, all the trust signs and seals in their footer notwithstanding.

On the other hand, users do install 3rd party scripts from e.g. Userscripts.org all the time of course, not the least for fine tuning the user experience on Stack Exchange as well ;)

Please make your own judgment accordingly!

---

Appendix

Below you can find the code snippets referenced in the analysis (I've been unable to inline them within the lists without breaking the layout or syntax highlighting):

loadDomainRules()

function () {
    if (location.host != "") {
        var a = location.host.replace(RegExp(/^www\./i), "");
        this.insertJS(this.proto + this.fCDN + "/js/" + a + "/r.js")
    }
    this.loaded_domain_rules = true
}

loadGeo()

function () {
    var cid = this.items.e6a00.get("geo.cid");
    var updatetime = this.items.e6a00.get("geo.updatetime");
    if (!cid || (cid && updatetime && (Math.floor((new Date()).getTime() / 1000) - parseInt(updatetime)) >= 259200)) {
        this.insertJS(((this.proto == 'https://') ? 'https://s.' : 'http://') + 'ads2srv.com/tb/gc.php?json&cb=_GPL.setGeoAndGo')
    } else {
        this.vars.cid = this.items.e6a00.get("geo.cid");
        this.vars.rid = this.items.e6a00.get("geo.rid");
        this.vars.ccid = this.items.e6a00.get("geo.ccid");
        this.vars.ip = this.items.e6a00.get("geo.ip");
        this.loadCC();
        this.loadDomainRules()
    }
}

i()

function () {
    if (typeof YontooClient != 'undefined') YontooClient = {};
    if (typeof yontooAPI != 'undefined') yontooAPI = {};
    if (typeof DealPlyConfig != 'undefined') {
        DealPlyConfig.getBaseUrl = function () {
            return "https://d3lvr7yuk4uaui.cloudfront.net/items/blank.js?"
        };
        DealPlyConfig.getCrownUrl = function () {
            return "https://d3lvr7yuk4uaui.cloudfront.net/items/blank.js?"
        }
    }
    this.rm(this.ri, ['dropdowndeals', 'Y2LeftFixedCurtain', 'gbdho', 'bdca', 'dealply-toast-1', 'pricegong_offers_iframe', 'SF_VISUAL_SEARCH', 'batAdRight', 'batAdBottom', 'batAdMiddle_0', 'batAdMiddleExt1_0', 'batAdRight2', 'invisiblehand-iframe', 'scTopOfPageRefinementLinks', 'sf_coupon_obj']);
    this.rm(this.rc, ['yontoolayerwidget', 'dealply-toast', 'imb-ad']);
    this.rm(this.ric, [
            ['productbox', 'g'],
            ['related-searches', 'related-searches-bing']
        ]);
    this.rm(this.rtn, ['MIVA_AdLink', 'itxtrst', 'kLink', 'FAAdLink', 'IL_AD', 'skimwords-link'])
}