New Relic's Overeager Browser Agent Injection

Published: March 9, 2018

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NOTE: This post is based on the the New Relic PHP Agent as of Version 7.6.0.201

Recently I received a report from a client which read something like this…

Checkout is blocked on our website. Customers cannot place orders. Help!

I navigated to the website in question, added a product to my shopping cart and, upon clicking the “checkout” button was directed to a screen where I was prompted to select my “complimentary sample product”.

There, I selected a random “sample product” at which point a “loading” overlay appeared on the screen. I waited a few seconds and soon realized the overlay wasn’t going to disappear. I was effectively “blocked” from getting to checkout…

Digging in I found that the issue was caused by unencoded injection of the New Relic Browser Agent JavaScript into a JSON AJAX response leading to a JavaScript parse error, which prevented the overlay from disappearing and success message from showing up.

Here I’ll provide more details on the issue and my findings…

How The Injection Works

Based on my testing, the PHP Agent will inject the first part of the browser agent immediately after it detects the string “<head>” in the response body and the second part immediately before the string “</body>”. This happens for any response with Content-Type of text/html, which is the default for PHP.

This can be demonstrated with this simple test case…

<?php

echo '<head>HELLO</body>';

With the PHP Agent installed you can expect to see the following response…

<head><script type="text/javascript">window.NREUM||(NREUM={}),__nr_require=function(e,t,n){function r(n){if(!t[n]){var o=t[n]={exports:{}};e[n][0].call(o.exports,function(t){var o=e[n][1][t];return r(o||t)},o,o.exports)}return t[n].exports}if("function"==typeof __nr_require)return __nr_require;for(var o=0;o<n.length;o++)r(n[o]);return r}({1:[function(e,t,n){function r(){}function o(e,t,n){return function(){return i(e,[f.now()].concat(u(arguments)),t?null:this,n),t?void 0:this}}var i=e("handle"),a=e(2),u=e(3),c=e("ee").get("tracer"),f=e("loader"),s=NREUM;"undefined"==typeof window.newrelic&&(newrelic=s);var p=["setPageViewName","setCustomAttribute","setErrorHandler","finished","addToTrace","inlineHit","addRelease"],d="api-",l=d+"ixn-";a(p,function(e,t){s[t]=o(d+t,!0,"api")}),s.addPageAction=o(d+"addPageAction",!0),s.setCurrentRouteName=o(d+"routeName",!0),t.exports=newrelic,s.interaction=function(){return(new r).get()};var m=r.prototype={createTracer:function(e,t){var n={},r=this,o="function"==typeof t;return i(l+"tracer",[f.now(),e,n],r),function(){if(c.emit((o?"":"no-")+"fn-start",[f.now(),r,o],n),o)try{return t.apply(this,arguments)}catch(e){throw c.emit("fn-err",[arguments,this,e],n),e}finally{c.emit("fn-end",[f.now()],n)}}}};a("setName,setAttribute,save,ignore,onEnd,getContext,end,get".split(","),function(e,t){m[t]=o(l+t)}),newrelic.noticeError=function(e){"string"==typeof e&&(e=new Error(e)),i("err",[e,f.now()])}},{}],2:[function(e,t,n){function r(e,t){var n=[],r="",i=0;for(r in e)o.call(e,r)&&(n[i]=t(r,e[r]),i+=1);return n}var o=Object.prototype.hasOwnProperty;t.exports=r},{}],3:[function(e,t,n){function r(e,t,n){t||(t=0),"undefined"==typeof n&&(n=e?e.length:0);for(var r=-1,o=n-t||0,i=Array(o<0?0:o);++r<o;)i[r]=e[t+r];return i}t.exports=r},{}],4:[function(e,t,n){t.exports={exists:"undefined"!=typeof window.performance&&window.performance.timing&&"undefined"!=typeof window.performance.timing.navigationStart}},{}],ee:[function(e,t,n){function r(){}function o(e){function t(e){return e&&e instanceof r?e:e?c(e,u,i):i()}function n(n,r,o,i){if(!d.aborted||i){e&&e(n,r,o);for(var a=t(o),u=m(n),c=u.length,f=0;f<c;f++)u[f].apply(a,r);var p=s[y[n]];return p&&p.push([b,n,r,a]),a}}function l(e,t){v[e]=m(e).concat(t)}function m(e){return v[e]||[]}function w(e){return p[e]=p[e]||o(n)}function g(e,t){f(e,function(e,n){t=t||"feature",y[n]=t,t in s||(s[t]=[])})}var v={},y={},b={on:l,emit:n,get:w,listeners:m,context:t,buffer:g,abort:a,aborted:!1};return b}function i(){return new r}function a(){(s.api||s.feature)&&(d.aborted=!0,s=d.backlog={})}var u="[email protected]",c=e("gos"),f=e(2),s={},p={},d=t.exports=o();d.backlog=s},{}],gos:[function(e,t,n){function r(e,t,n){if(o.call(e,t))return e[t];var r=n();if(Object.defineProperty&&Object.keys)try{return Object.defineProperty(e,t,{value:r,writable:!0,enumerable:!1}),r}catch(i){}return e[t]=r,r}var o=Object.prototype.hasOwnProperty;t.exports=r},{}],handle:[function(e,t,n){function r(e,t,n,r){o.buffer([e],r),o.emit(e,t,n)}var o=e("ee").get("handle");t.exports=r,r.ee=o},{}],id:[function(e,t,n){function r(e){var t=typeof e;return!e||"object"!==t&&"function"!==t?-1:e===window?0:a(e,i,function(){return o++})}var o=1,i="[email protected]",a=e("gos");t.exports=r},{}],loader:[function(e,t,n){function r(){if(!x++){var e=h.info=NREUM.info,t=d.getElementsByTagName("script")[0];if(setTimeout(s.abort,3e4),!(e&&e.licenseKey&&e.applicationID&&t))return s.abort();f(y,function(t,n){e[t]||(e[t]=n)}),c("mark",["onload",a()+h.offset],null,"api");var n=d.createElement("script");n.src="https://"+e.agent,t.parentNode.insertBefore(n,t)}}function o(){"complete"===d.readyState&&i()}function i(){c("mark",["domContent",a()+h.offset],null,"api")}function a(){return E.exists&&performance.now?Math.round(performance.now()):(u=Math.max((new Date).getTime(),u))-h.offset}var u=(new Date).getTime(),c=e("handle"),f=e(2),s=e("ee"),p=window,d=p.document,l="addEventListener",m="attachEvent",w=p.XMLHttpRequest,g=w&&w.prototype;NREUM.o={ST:setTimeout,SI:p.setImmediate,CT:clearTimeout,XHR:w,REQ:p.Request,EV:p.Event,PR:p.Promise,MO:p.MutationObserver};var v=""+location,y={beacon:"bam.nr-data.net",errorBeacon:"bam.nr-data.net",agent:"js-agent.newrelic.com/nr-1071.min.js"},b=w&&g&&g[l]&&!/CriOS/.test(navigator.userAgent),h=t.exports={offset:u,now:a,origin:v,features:{},xhrWrappable:b};e(1),d[l]?(d[l]("DOMContentLoaded",i,!1),p[l]("load",r,!1)):(d[m]("onreadystatechange",o),p[m]("onload",r)),c("mark",["firstbyte",u],null,"api");var x=0,E=e(4)},{}]},{},["loader"]);</script>HELLO<script type="text/javascript">window.NREUM||(NREUM={});NREUM.info={"beacon":"bam.nr-data.net","licenseKey":"a44ba31e2d","applicationID":"87109248","transactionName":"ZVNWMBZQC0VTAkxcV1wZYRYNHgFTXw4WRVBC","queueTime":0,"applicationTime":1,"atts":"SRRVRl5KGEs=","errorBeacon":"bam.nr-data.net","agent":""}</script></body>

The injection happens after PHP has finished executing and preparing the response. This means that if the application sends back a JSON response that contains the string “<head>” and doesn’t set an application/json Content-Type response header, New Relic will inject the browser agent JavaScript causing malformed JSON.

This can be demo-ed as follows…

<?php

$response = array(
	'content' => '<html><head></head><body><h1>Hello</h1></body></html>'
);

echo json_encode($response);

This will result in the following response…

{"content":"<html><head><script type="text/javascript">window.NREUM||(NREUM={}),__nr_require=function(e,t,n){function r(n){if(!t[n]){var o=t[n]={exports:{}};e[n][0].call(o.exports,function(t){var o=e[n][1][t];return r(o||t)},o,o.exports)}return t[n].exports}if("function"==typeof __nr_require)return __nr_require;for(var o=0;o<n.length;o++)r(n[o]);return r}({1:[function(e,t,n){function r(){}function o(e,t,n){return function(){return i(e,[f.now()].concat(u(arguments)),t?null:this,n),t?void 0:this}}var i=e("handle"),a=e(2),u=e(3),c=e("ee").get("tracer"),f=e("loader"),s=NREUM;"undefined"==typeof window.newrelic&&(newrelic=s);var p=["setPageViewName","setCustomAttribute","setErrorHandler","finished","addToTrace","inlineHit","addRelease"],d="api-",l=d+"ixn-";a(p,function(e,t){s[t]=o(d+t,!0,"api")}),s.addPageAction=o(d+"addPageAction",!0),s.setCurrentRouteName=o(d+"routeName",!0),t.exports=newrelic,s.interaction=function(){return(new r).get()};var m=r.prototype={createTracer:function(e,t){var n={},r=this,o="function"==typeof t;return i(l+"tracer",[f.now(),e,n],r),function(){if(c.emit((o?"":"no-")+"fn-start",[f.now(),r,o],n),o)try{return t.apply(this,arguments)}catch(e){throw c.emit("fn-err",[arguments,this,e],n),e}finally{c.emit("fn-end",[f.now()],n)}}}};a("setName,setAttribute,save,ignore,onEnd,getContext,end,get".split(","),function(e,t){m[t]=o(l+t)}),newrelic.noticeError=function(e){"string"==typeof e&&(e=new Error(e)),i("err",[e,f.now()])}},{}],2:[function(e,t,n){function r(e,t){var n=[],r="",i=0;for(r in e)o.call(e,r)&&(n[i]=t(r,e[r]),i+=1);return n}var o=Object.prototype.hasOwnProperty;t.exports=r},{}],3:[function(e,t,n){function r(e,t,n){t||(t=0),"undefined"==typeof n&&(n=e?e.length:0);for(var r=-1,o=n-t||0,i=Array(o<0?0:o);++r<o;)i[r]=e[t+r];return i}t.exports=r},{}],4:[function(e,t,n){t.exports={exists:"undefined"!=typeof window.performance&&window.performance.timing&&"undefined"!=typeof window.performance.timing.navigationStart}},{}],ee:[function(e,t,n){function r(){}function o(e){function t(e){return e&&e instanceof r?e:e?c(e,u,i):i()}function n(n,r,o,i){if(!d.aborted||i){e&&e(n,r,o);for(var a=t(o),u=m(n),c=u.length,f=0;f<c;f++)u[f].apply(a,r);var p=s[y[n]];return p&&p.push([b,n,r,a]),a}}function l(e,t){v[e]=m(e).concat(t)}function m(e){return v[e]||[]}function w(e){return p[e]=p[e]||o(n)}function g(e,t){f(e,function(e,n){t=t||"feature",y[n]=t,t in s||(s[t]=[])})}var v={},y={},b={on:l,emit:n,get:w,listeners:m,context:t,buffer:g,abort:a,aborted:!1};return b}function i(){return new r}function a(){(s.api||s.feature)&&(d.aborted=!0,s=d.backlog={})}var u="[email protected]",c=e("gos"),f=e(2),s={},p={},d=t.exports=o();d.backlog=s},{}],gos:[function(e,t,n){function r(e,t,n){if(o.call(e,t))return e[t];var r=n();if(Object.defineProperty&&Object.keys)try{return Object.defineProperty(e,t,{value:r,writable:!0,enumerable:!1}),r}catch(i){}return e[t]=r,r}var o=Object.prototype.hasOwnProperty;t.exports=r},{}],handle:[function(e,t,n){function r(e,t,n,r){o.buffer([e],r),o.emit(e,t,n)}var o=e("ee").get("handle");t.exports=r,r.ee=o},{}],id:[function(e,t,n){function r(e){var t=typeof e;return!e||"object"!==t&&"function"!==t?-1:e===window?0:a(e,i,function(){return o++})}var o=1,i="[email protected]",a=e("gos");t.exports=r},{}],loader:[function(e,t,n){function r(){if(!x++){var e=h.info=NREUM.info,t=d.getElementsByTagName("script")[0];if(setTimeout(s.abort,3e4),!(e&&e.licenseKey&&e.applicationID&&t))return s.abort();f(y,function(t,n){e[t]||(e[t]=n)}),c("mark",["onload",a()+h.offset],null,"api");var n=d.createElement("script");n.src="https://"+e.agent,t.parentNode.insertBefore(n,t)}}function o(){"complete"===d.readyState&&i()}function i(){c("mark",["domContent",a()+h.offset],null,"api")}function a(){return E.exists&&performance.now?Math.round(performance.now()):(u=Math.max((new Date).getTime(),u))-h.offset}var u=(new Date).getTime(),c=e("handle"),f=e(2),s=e("ee"),p=window,d=p.document,l="addEventListener",m="attachEvent",w=p.XMLHttpRequest,g=w&&w.prototype;NREUM.o={ST:setTimeout,SI:p.setImmediate,CT:clearTimeout,XHR:w,REQ:p.Request,EV:p.Event,PR:p.Promise,MO:p.MutationObserver};var v=""+location,y={beacon:"bam.nr-data.net",errorBeacon:"bam.nr-data.net",agent:"js-agent.newrelic.com/nr-1071.min.js"},b=w&&g&&g[l]&&!/CriOS/.test(navigator.userAgent),h=t.exports={offset:u,now:a,origin:v,features:{},xhrWrappable:b};e(1),d[l]?(d[l]("DOMContentLoaded",i,!1),p[l]("load",r,!1)):(d[m]("onreadystatechange",o),p[m]("onload",r)),c("mark",["firstbyte",u],null,"api");var x=0,E=e(4)},{}]},{},["loader"]);</script><\/head><body><h1>Hello<\/h1><\/body><\/html>"}

Fortunately, this can be mitigated by simply setting the correct Content-Type for the JSON response, which is what we wound up doing for the client in this case…

<?php

$response = array(
	'content' => '<html><head></head><body><h1>Hello</h1></body></html>'
);

header('Content-Type: application/json');
echo json_encode($response);

And the response…

{"content":"<html><head><\/head><body><h1>Hello<\/h1><\/body><\/html>"}

My Thoughts On The Issue

While on one side of the argument, the application should just set the correct Content-Type for JSON responses, on the other side, New Relic could be a bit more cautious to prevent against this. For example, if the first byte of the response is a “{” it’s probably a good idea to assume that the response is JSON and avoid injecting the browser agent, regardless of the Content-Type.

I would argue that it’s better to err on the side of caution here as I’d prefer to lose monitoring for some responses over completely breaking application functionality due to mangling of response bodies.

Some Other Reference Points

Also, it’s worth noting that this sample product case is not the only example of this behavior causing issues.

In fact, the Aligent_NewRelicFix Magento module was built to fix the same issue which occurs when viewing transactional email templates in the Magento admin panel.

Further, there’s an additional issue in Magento 2 which can cause rendering of UI Components to fail. This issue was in fact even specifically addressed in version 7.6.0.201 of the New Relic PHP Agent.

In some cases, Magento 2’s UI Component JSON data sources return with an (incorrect) Content-Type of text/html. This resulted in auto instrumentation insertions into JSON data that contained a <head> string. We now identify these specific JSON data sources and ensure the auto instrumentation is not inserted into this JSON data.

PHP Agent 7.6.0.201 Release Notes

Max Chadwick Hi, I'm Max!

I'm a software developer who mainly works in PHP, but also dabbles in Ruby and Go. Technical topics that interest me are monitoring, security and performance.

During the day I solve challenging technical problems at Something Digital where I mainly work with the Magento platform. I also blog about tech, work on open source and hunt for bugs.

If you'd like to get in touch with me the best way is on Twitter.