Security Blog

Fuzzing Closed Source PDF Viewers

This blog post covers typical problems which arise when fuzzing closed source PDF viewers and possible approaches to these problems. Hereby it focuses on both: Input-Minimization and Non-Terminating programs. The approaches were found and implemented as part of my master thesis which I have written at TU Darmstadt, Germany in cooperation with Fraunhofer SIT.

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Automating local DTD discovery for XXE exploitation

Last month, we presented at Hack In Paris (France) a XML External Entities (XXE) exploitation workshop. It showcase methods to exploit XXE with numerous obstacles. Today, we present our method to exploit XXEs with a local Document Type Declaration (DTD) file. More specifically, how we built a huge list of reusable DTD files.

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Java Remote Code Execution Potpourri

Some time ago; we published a blog about jenkins-fsb, a preconfigured Jenkins instance for efficiently using the plug-in, Find Security Bugs. In that blog post, there was an indication about multiple vulnerabilities having been found but not disclosed. Well, today we are sharing more details about the process of finding four different kinds of remote code execution in modern Java applications.

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ESI Injection Part 2: Abusing specific implementations

Last year, we published a blog post about the injection of ESI tags in pages to fool the web cache proxy, and in August 2018, our colleague Louis Dion-Marcil spoke at Defcon about the discovery of the ESI Injection uncovered by the GoSecure intrusion testing team. For those interested, the presentation has been released on the Defcon YouTube channel. Defcon and Black Hat gave us an opportunity to unveil how ESI implementations can lead to session leakage through the client web browser without any malicious JavaScript.

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Abusing Unsafe Defaults in Active Directory Domain Services: A Real-World Case Study

This past July, Kevin Robertson from NetSPI released a blog post entitled, “Beyond LLMNR/NBNS Spoofing – Exploiting Active Directory-Integrated DNS,” which introduced a new technique (to us at least) targeting weak default access control in Active Directory Domain Services. At GoSecure, since most of our engagements require some level of Active Directory security assessment, we followed our interest and decided to find a way to reliably exploit it.

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