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When shellcode that contains nulls is injected in this way, only part of the shellcode would be injected, making it incapable of running successfully. To produce null-free shellcode from shellcode that contains null bytes, one can substitute machine instructions that contain zeroes with instructions that have the same effect but are free of nulls.
At the end of the attacker-supplied data, after the no-op instructions, the attacker places an instruction to perform a relative jump to the top of the buffer where the shellcode is located. This collection of no-ops is referred to as the "NOP-sled" because if the return address is overwritten with any address within the no-op region of the ...
0x90 is the one-byte encoding for XCHG AX,AX in 16-bit code and XCHG EAX,EAX in 32-bit code. In long mode, XCHG RAX,RAX requires two bytes, as it would begin with an REX.W prefix, making the encoding 0x48 0x90. However, 0x90 is interpreted as a NOP in long mode regardless of whether it is preceded by 0x48. [2] multi-byte NOP
Therefore, the bytes on the heap are restricted to represent valid addresses within the heap spray itself, holding valid instructions for the target architecture, so the application will not crash. It is therefore common to spray with a single byte that translates to both a valid address and a NOP or NOP-like instruction on the target architecture.
1. The program calculates the value of "50 bytes after where the algorithm ends" 2. It sets the stack pointer to point to that location 3. It calculates a hexadecimal C3C3 and places it in the AX-cpu register. (Sort of like a very-very-fast variable) 4. It pushes (overwrites) "C3C3" to the stack 5. It jumps to the written code.
A binary-to-text encoding is encoding of data in plain text.More precisely, it is an encoding of binary data in a sequence of printable characters.These encodings are necessary for transmission of data when the communication channel does not allow binary data (such as email or NNTP) or is not 8-bit clean.
16-bit words are stored little-endian with least significant bytes at the lower address. Words are always aligned to even memory addresses. Words can be held in registers R0 through R7. 32-bit double words in the Extended Instruction Set (EIS) can only be stored in register pairs with the lower word being stored in the lower-numbered register.
Canaries or canary words or stack cookies are known values that are placed between a buffer and control data on the stack to monitor buffer overflows. When the buffer overflows, the first data to be corrupted will usually be the canary, and a failed verification of the canary data will therefore alert of an overflow, which can then be handled, for example, by invalidating the corrupted data.