Hacking

XSS flaw would have allowed hackers access to Google’s network and impersonate its employees

Bug hunter Thomas Orlita discovered an XSS vulnerability in Google’s Invoice Submission Portal that would have allowed attackers access to Google’s internal network

The Czech researcher Thomas Orlita discovered an XSS vulnerability in Google’s Invoice Submission Portal that would have allowed attackers access to part of Google’s internal network.

The Google Invoice Submission Portal is a public portal used by Google’s business partners to submit invoices.

An attacker could also exploit the flaw to steal Google employee cookies for internal apps and hijack accounts or send spear-phishing messages.

The attack was devised by the expert in February, and Google addressed the issue in mid-April after the researcher reported it to the tech giant.

Orlita explained that an attacker could have uploaded malformed files in the Google Invoice Submission Portal, via the Upload Invoice field.

The expert noticed that the ‘upload’ feature for actual invoice in PDF format could be abused to upload HTML files. The attacker had to intercept a request and change the uploaded file’s filename and Content-Type properties to HTML.

Using this trick it was possible to store malicious files in Google’s invoicing system and would have executed automatically when an employee tried to access it.

“Since this is just a front-end validation, it doesn’t stop us from changing the file type when sending the upload POST request. Once we select any PDF file, an upload request is fired. We can intercept the request using a web proxy debugger and change the filename and the contents from .pdf to .html.” reads the analysis published by the expert.

Orlita uploaded an HTML file including an XSS payload that, when triggered, would send him an email every time it was loaded.

A few days later, the expert received an email message showing that the JavaScript code in the XSS payload had been executed on the googleplex.com domain.

This domain is used by Google for hosting internal websites and apps. If you attempt to access the domain you will be redirected to a Google Corp login page for Google employees that requires the authentication.

“The DOM of the page matches the XSS payload that was put instead of the PDF file. We can see that this URL is used for displaying a PDF file. But since the Content-Type of the uploaded file was changed from application/pdf to text/html, it displayed and rendered the XSS payload instead of the PDF.” continues the expert.

According to the researcher, it was possible to exploit the flaw to execute arbitrary code on behalf of Google employees and gain access to sensitive information.

The expert pointed out that many Google internal apps are hosted on the googleplex.com domain, making this issue a gift for the attackers,

Below the timeline for the flaw:

21.02.2019: Vulnerability reported
22.02.2019: Priority changed to P2 
22.02.2019: Added more information 
25.02.2019: Accepted and priority changed to P1 
06.03.2019: Reward issued 
26.03.2019: A fix has been implemented 
11.04.2019: Issue marked as fixed

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Pierluigi Paganini

(SecurityAffairs – XSS, hacking)

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Pierluigi Paganini

Pierluigi Paganini is member of the ENISA (European Union Agency for Network and Information Security) Threat Landscape Stakeholder Group and Cyber G7 Group, he is also a Security Evangelist, Security Analyst and Freelance Writer. Editor-in-Chief at "Cyber Defense Magazine", Pierluigi is a cyber security expert with over 20 years experience in the field, he is Certified Ethical Hacker at EC Council in London. The passion for writing and a strong belief that security is founded on sharing and awareness led Pierluigi to find the security blog "Security Affairs" recently named a Top National Security Resource for US. Pierluigi is a member of the "The Hacker News" team and he is a writer for some major publications in the field such as Cyber War Zone, ICTTF, Infosec Island, Infosec Institute, The Hacker News Magazine and for many other Security magazines. Author of the Books "The Deep Dark Web" and “Digital Virtual Currency and Bitcoin”.

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