Uploaded December 2019 | Updated September 2026, 5 days ago
We show practical attacks against OpenPGP and S/MIME encryption and digital signatures in the context of email. Instead of targeting the underlying cryptographic primitives, our attacks abuse legitimate features of the MIME standard and HTML, as supported by email clients, to deceive the user regarding the actual message content. We demonstrate how the attacker can unknowingly abuse the user as a decryption oracle by replying to an unsuspicious looking email. Using this technique, the plaintext of hundreds of encrypted emails can be leaked at once. Furthermore, we show how users could be tricked into signing arbitrary text by replying to emails containing CSS conditional rules. An evaluation shows that 17 out of 19 OpenPGP-capable email clients, as well as 21 out of 22 clients supporting S/MIME, are vulnerable to at least one attack. We provide different countermeasures and discuss their advantages and disadvantages
Presenters:
Jens Müller - Ruhr University Bochum
Jens Müller is a PhD student at the Chair for Network and Data Security, Ruhr University Bochum, Germany. His research interests are legacy protocols and data formats, for which he loves to investigate what could possibly go wrong in a modern world. He has experience as a speaker on international security conferences (BlackHat, IEEE S&P, OWASP) and as a freelancer in network penetration testing and security auditing. Besides breaking thinks, he develops free open source software, for example, tools related to network printer exploit^H^H^H^H^H^H^H, um, "debugging". Twitter: @jensvoid Websites: nds.ruhr-uni-bochum.de/chair/people/jmueller hacking-printers.net
We show practical attacks against OpenPGP and S/MIME encryption and digital signatures in the context of email. Instead of targeting the underlying cryptographic primitives, our attacks abuse legitimate features of the MIME standard and HTML, as supported by email clients, to deceive the user regarding the actual message content. We demonstrate how the attacker can unknowingly abuse the user as a decryption oracle by replying to an unsuspicious looking email. Using this technique, the plaintext of hundreds of encrypted emails can be leaked at once. Furthermore, we show how users could be tricked into signing arbitrary text by replying to emails containing CSS conditional rules. An evaluation shows that 17 out of 19 OpenPGP-capable email clients, as well as 21 out of 22 clients supporting S/MIME, are vulnerable to at least one attack. We provide different countermeasures and discuss their advantages and disadvantages
Presenters:
Jens Müller - Ruhr University Bochum
Jens Müller is a PhD student at the Chair for Network and Data Security, Ruhr University Bochum, Germany. His research interests are legacy protocols and data formats, for which he loves to investigate what could possibly go wrong in a modern world. He has experience as a speaker on international security conferences (BlackHat, IEEE S&P, OWASP) and as a freelancer in network penetration testing and security auditing. Besides breaking thinks, he develops free open source software, for example, tools related to network printer exploit^H^H^H^H^H^H^H, um, "debugging". Twitter: @jensvoid Websites: nds.ruhr-uni-bochum.de/chair/people/jmueller hacking-printers.net
![Black Hat USA 2018 - Mainframe [z/OS] Reverse Engineering and Exploit Development](https://i.ytimg.com/vi/opBLBYAR8tU/mqdefault.jpg "Black Hat USA 2018 - Mainframe [z/OS] Reverse Engineering and Exploit Development
Speak with any Fortune 500 running mainframe and theyll tell you two things: (1) without their mainframes theyd be out of business (2) they do not conduct any security research on them, let alone vulnerability scans. The most infuriating part is that mainframes are simply computers, theyre different from what youre used to, but that doesnt mean they cant be hacked. Previous talks about this topic have covered the platform from a high level, imploring you to do the basics. This talk continues this series of talks, given by others, around mainframe hacking. Previously covered topics included network penetration testing and privilege escalation. To complement those talks, this talk will expose attendees to the various tools that exist on the platform to help you do your own reverse engineering, followed by detailed steps on how to start your own exploit development. Attendees will learn what debuggers are available on the platform, such as dbx and ASMIDF, as well as the challenges youll have using them. After learning how to RE, attendees will then learn how to develop their own exploits and buffer overflows on the platform using C, assembler and JCL. A demo program will be used to teach all these items so people can follow along. Topics included in this discussion are APF authorization, bypassing RACF/ACEE, TSO, Unix System Services.")
