Category Archives: Penetration Testing

The Case of the Customer Data and the Third-Party Analytics Site

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I recently had an article published on the NCC Group blog about a pentest during which it became clear that customer personal data was being sent to a third party. It’s common for websites to use metrics/analytics services to collect usage data on how users are interacting with the sites. I thought it would be useful to highlight the danger of sensitive data being accidentally sent to third parties without due care and attention paid to GDPR. Have a read!

JWT Attack Walk-Through

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Over on the NCC Group website I published a solution to an open demonstration of the well-known JSON Web Token (JWT) algorithm confusion vulnerability (the one where you swap the token algorithm from ‘RS’ to ‘HS’ and sign your payload with the public key). I use OpenSSL to gain full visibility of what’s happening and, by walking through the method, if you ever need to test this vulnerability yourself, it will hopefully help to avoid false negatives.

Missing XSS flaws with innerHTML and jQuery

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I thought a couple of gotchas when testing for XSS could be a useful post. Not new, especially, but I haven’t posted for a while. It shows how you might think you’ve covered an area of a web application and declared it free from XSS but in fact there might be a bug left behind. Continue reading →

From CSV to CMD to qwerty

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The ongoing breach stories of targeted email campaigns harbouring malicious attachments made me think of writing up a summary of a presentation I gave at the amazing NCC Con held in Dublin in January this year. The talk was based on a pentesting war story that started off exploiting the old (but I believe often overlooked) Dynamic Data Exchange (DDE) trick to go from an Excel export function in a web app to OS code running on users’ workstations. From there, the story takes us on to domain creds via some NTLMv2 theory (without a pentest laptop), a bug in hashcat and a new script “catflap”. Continue reading →

The Why Behind Web Application Penetration Test Prerequisites

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Before a web application penetration test is scheduled to start, the company performing the test will contact the client with a list of considerations and configurations that are required before the test can begin. Sadly, the importance of these can be lost in amongst the frenzy of ensuring the system is ready on time, or perhaps because the items listed don’t seem necessary. My whitepaper aims to address the latter, providing an explanation of the why behind the prerequisites, together with some general pre-test points for consideration. It is aimed at anyone who is charged with preparing for a web application penetration test, from project managers to developers, and as such it is written for both technical and non-technical readers. The paper ends with a one-page quick reference guide to help with future tests, which is available as a standalone document here.

Testing for Anti-Virus on File Upload

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One of the issues on a standard web app checklist is to test whether or not an application that supports file upload is scanning those files for malware. This article reviews the methodology and highlights the danger of corrupting an EICAR test file so that it no longer acts as a valid test. It is based on an internal presentation I gave, the slides for which are here. Continue reading →

When HTML Encoding Helped XSS

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Recently I was pentesting a web app that had an unauthenticated XSS vulnerability but there was some heavy filtering in place. Nonetheless I was able to achieve session fixation using a combination of a technique I previously explained and some fun filter workarounds – including using the application’s own defensive HTML encoding to create a working XSS payload! Continue reading →

SS-Hell: the Devil is in the Details

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Penetration test reports commonly contain mention of vulnerabilities in SSL/TLS (hereafter referred to as just SSL). In many cases, this is due to system administrators not understanding the details of these services’ configuration and assuming that simply using SSL provides security. The issues identified during penetration tests are usually low in severity, as an average attacker would find them difficult to exploit, but they should be taken seriously to ensure that data in transit is properly secured. If something’s worth doing, it’s worth doing well. This whitepaper, co-written with Will Alexander, discusses how organisations can avoid SSL issues commonly found during penetration tests, ensure that data in transit is properly secured and ultimately instil in users a sense of confidence that their information is adequately protected.

Thoughts on Testing for POODLE

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I recently did an internal presentation on POODLE – what the flaw is and how to test for it – and a version of the slides can be found here. Obviously much has been written about the vulnerability, its mitigations and what the future holds. What follows expands on the testing aspect of the presentation, with a few pointers on manual checks if you feel you need to verify or clarify – and possibly even add to – what the tools are telling you. Continue reading →