@cypnk since the previous post is Doing Numbers, folks may also enjoy this 2021 zero-click iMessage exploit by notorious Israeli spyware-for-despotic-nation-states firm NSO Group, which involved sending a .gif file that was actually a PDF that used the now-uncommon JBIG2 black-and-white image compression format which, surprisingly, is Turing-complete.

As this Project Zero blog post explains,

JBIG2 doesn't have scripting capabilities, but when combined with a vulnerability, it does have the ability to emulate circuits of arbitrary logic gates operating on arbitrary memory. So why not just use that to build your own computer architecture and script that!? That's exactly what this exploit does. Using over 70,000 segment commands defining logical bit operations, they define a small computer architecture with features such as registers and a full 64-bit adder and comparator which they use to search memory and perform arithmetic operations. It's not as fast as Javascript, but it's fundamentally computationally equivalent.