Years ago, the author was involved in the iOS tweak development scene, creating products and tools that modified iOS system behavior. They decided to write their own jailbreak to remove some of the mystery surrounding the process. After acquiring older iPhones and researching boot ROM vulnerabilities, they discovered limera1n, an exploit that allowed them to gain code execution on the device. They were surprised to find that they could read memory from the device over USB and used this capability to gather debug data. They also used Rust to write their payload and developed a script to extract the raw machine code for execution on the iPhone.
https://axleos.com/exploiting-the-iphone-4-part-1-gaining-entry/