Nils Emmerich – Insinuator.net

October 10, 2023 by Nils Emmerich

Lua-Resty-JWT Authentication Bypass

I was writing some challenges for PacketWars at TROOPERS22. One was intended to be a JWT key confusion challenge where the public key from an RSA JWT should be recovered and used to sign a symmetric JWT. For that, I was searching for a library vulnerable to JWT key confusion by default and found lua-resty-jwt. The original repository by SkyLothar is not maintained and different from the library that is installed with the LuaRocks package manager. The investigated library is a fork of the original repository, maintained by cdbattags in version 0.2.3 and was downloaded more than 4.8 million times according to LuaRocks.

While looking at the source code I found a way to circumvent authentication entirely.

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Misc

September 2, 2020 by Nils Emmerich

Java Buffer Overflow with ByteBuffer (CVE-2020-2803) and Mutable MethodType (CVE-2020-2805) Sandbox Escapes

Years ago, Java could be used on websites trough applets. To make these applets secure and not let them access files or do other dangerous stuff, Java introduced the SecurityManager. Before some action was performed, the SecurityManager was asked if the code is privileged to perform this action. However, since the SecurityManager lives in the same running program and can be accessed via System.getSecurityManager(), there existed some ways to remove it. Continue reading “Java Buffer Overflow with ByteBuffer (CVE-2020-2803) and Mutable MethodType (CVE-2020-2805) Sandbox Escapes”

Breaking

September 20, 2019 by Nils Emmerich

Jenkins – Groovy Sandbox breakout (SECURITY-1538 / CVE-2019-10393, CVE-2019-10394, CVE-2019-10399, CVE-2019-10400)

Recently, I discovered a sandbox breakout in the Groovy Sandbox used by the Jenkins script-security Plugin in their Pipeline Plugin for build scripts. We responsibly disclosed this vulnerability and in the current version of Jenkins it has been fixed and the according Jenkins Security Advisory 2019-09-12 has been published. In this blogpost I want to report a bit on the technical details of the vulnerability.

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Misc

July 26, 2019 by Nils Emmerich

LibreOffice – A Python Interpreter (code execution vulnerability CVE-2019-9848)

While waiting for a download to complete, I stumbled across an interesting blogpost. The author describes a flaw in LibreOffice that allowed an attacker to execute code. Since this was quite recent, I was interested if my version is vulnerable to this attack and how they fixed it. Thus, I looked at the sources and luckily it was fixed. What I didn’t know before however was, that macros shipped with LibreOffice are executed without prompting the user, even on the highest macro security setting. So, if there would be a system macro from LibreOffice with a bug that allows to execute code, the user would not even get a prompt and the code would be executed right away. Therefor, I started to have a closer look at the source code and found out that exactly this is the case!

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