Shellcode

When writing or modifying custom assembly shellcode (such as egg hunters, socket reuse payloads, or stagers), you must verify that the payload functions correctly before embedding it into a full exploit delivery chain. A standard C test harness executes shellcode by casting a char array in memory to a function pointer and calling it directly. The C Test Harness #include <stdio.h> #include <string.h> // Example: Software breakpoint (INT3) or your target shellcode const char shellcode[] = "\x31\xc0\x50\x68\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\x50\x53\x89\xe1\xb0\x0b\xcd\x80"; int main(int argc, char **argv) { printf("Shellcode length: %zu bytes\n", strlen(shellcode)); // Cast the array address to a callable function pointer int (*ret)() = (int (*)())shellcode; // Transfer control flow to shellcode ret(); return 0; } Compilation Flags: Disabling Modern Mitigations Modern compilers enable Stack Canaries and enforce Non-Executable Memory (DEP / NX) by default. If you attempt to execute data placed in the .rodata or .data section without special flags, the kernel terminates the process with a SIGSEGV / segmentation fault. ...

Level 5 of the Smash The Stack IO wargame presents a classic stack-based buffer overflow scenario. Executing the binary simply echoes the supplied command-line argument: level5@io:/levels$ ./level05 test test Analyzing the Source Code The source file level05.c shows an unbounded strcpy into a fixed 128-byte stack buffer: #include <stdio.h> #include <string.h> int main(int argc, char **argv) { char buf[128]; if (argc < 2) return 1; strcpy(buf, argv[1]); printf("%s\n", buf); return 0; } Because strcpy() copies until it hits a null byte without checking the destination bounds of buf[128], an argument exceeding 128 bytes overwrites adjacent stack data, including the saved base pointer (EBP) and return address (EIP). ...