Difficulty: Beginner
Flag: HCS{Buff3r_0v3rfl0wwwwww}
This one was a relatively easy one. Initially we're provided with a TUI interface and its source code.
The interface is a simple one, just an ascii (UTF-8 (?), I wasn't really sure tbh, emotes worked, so probably 🤷) input to work with.
Inspecting the source code, the give_flag function is called by a segmentation fault handler.
void sigsegv_handler(int sig){
give_flag();
}
void setup(){
signal(SIGSEGV, sigsegv_handler); // Set up signal handler
}This tells me that this has got to do something with faulty memory access, and looking at the code further down confirms this.
void vuln(){
char buffer[0x100];
gets(buffer);
}A string buffer is allocated for 0x100, so 256 bytes.
Now, all we have to do is spam it to overflow the buffer and cause a segfault. 👏
Yang ini lumayan gampang sih. Jadi awalnya kita dikasih antarmuka TUI dan source codenya.
Antarmukanya simpel, cumman input ascii (UTF-8 (?), ga yakin sih, emoji bisa, jadi mungkin 🤷).
Ngelihat di source codenya, function give_flag dijalankan oleh handler segmentation fault.
void sigsegv_handler(int sig){
give_flag();
}
void setup(){
signal(SIGSEGV, sigsegv_handler); // Set up signal handler
}Disini aku menyimpulkan bahwa ini pasti berhubungan dengan memori, dan ngelihat kebawah lagi membenarkan ini.
void vuln(){
char buffer[0x100];
gets(buffer);
}Buffer string dialokasikan hingga 0x100, so 256 bytes.
Nah, kita tinggal spam aja deh sampe segfault. 👏