UAF | UAF - Universal Authentication Framework | Authentication library

I am new to assembly programming. I wrote a small program to add two numbers.

I have to scrape a website, which requires a login token. The value is being replaced later via JS.

Let's say I have a very simple instruction mov eax,12345h. I assembled it using fasm and generated a bin file. When i checked the opcode of above instruction using hex editor it gave 66 B8 45 23 01 00 as the equivalent hex code. Now from what I have studied, I was expecting the first byte to be 0xb8 to represent the "load a 32-bit constant into eax" instruction and rest four bytes to be same as above. The aritcle that I mentioned also states that the same 0xb8 instruction that loads a 32-bit constant into eax can be used with a 0x66 prefix to load a 16-bit constant but clearly I am not loading a 16 bit constant in my program. Still the resulting opcode in my case starts with 66 as the first byte. Now I am not able to understand from where this 66 came ? Is there any different behavior in case of fasm ?

I am trying to understand how Rust's lifetime annotations help catch use-after-free (UAF) issues without compromising on functionality. Here is the code I have :

I am implementing the generate First and Follow set algorithms for compilers.

Here is the type definition for First Set and Follow Set elements:

I am playing with use-after-free vulnerability in Firefox build with Address Sanitizer. Suppose in an exploitation of a use-after-free vulnerability, we manage to allocate a new object B at where the freed object A was placed and hence the dangling pointer points to somewhere inside the new object B, I have two questions:

(1) when we dereference the dangling pointer, will ASAN still detect and report use-after-free related to the dangling pointer and the freed object?

(2) if dereference of dangling pointer now causes a crash due to the fact that it is pointing to a different object (B), then does ASAN detect UAF before the crash or after the crash?