Why Can't We Jump Directly from SEH?
In many cases, there may be significant padding or unused space between where control is transferred after SEH handling and where your shellcode resides. The jumpcode ensures that:
The stack pointer (ESP) is adjusted correctly to skip over this unused space. Execution flow reliably lands in your shellcode, even if there are gaps or misalignments. Without this adjustment, your exploit might crash or fail because it would attempt to execute invalid or unintended instructions.
The jumpcode is essential because it:
Adjusts the stack pointer (ESP) to skip unnecessary data after SEH handling. Redirects execution flow reliably into your shellcode using jmp esp. This ensures that your exploit works as intended, even when there are large gaps or misalignments in memory between SEH and your actual payload.