Alphanumeric shellcode

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Alphanumeric

shellcode is similar to ascii shellcode in that it is used to bypass character filters and evade intrusion-detection

during buffer overflow exploitation

This article documents alphanumeric code on multiple architectures, but primarily the 64 bit x86

architecture.

Alphanumeric shellcode requires a basic understanding of

bitwise math, assembly and shellcode

Contents

1 Available x86_64 instructions

2 Alphanumeric opcode compatibility

2.1 Alphanumeric inter-compatible x86 opcodes

2.2 15 byte architecture detection shellcode

3 Alphanumeric x86_64 register value and data manipulation

3.1 Push: alphanumeric x86_64 registers

3.2 Pop: alphanumeric x86_64 registers

3.3 Prefixes

3.4Operands

3.5 The rbx, rsp, and rbp registers

3.6 Xor

3.7 The rsi and rdi registers

3.8 Example: ZeroingOut x86_64 CPURegisters

4 64 bit shellcode:Conversion to alphanumeric code

4.1 bof.c

4.2 Starting shellcode (64-bit execve /bin/sh)

4.3 Shellcode Analysis

4.4 Stack Analysis

4.5 TheOffset

4.6 The Syscall

4.7 Arguments

4.7.1 Stack Space

4.7.2 Register Initialization

4.7.3 String Argument

4.7.4 Final Registers

4.8 Final Code

4.9 Successful OverflowTest

Download:

http://dl.packetstormsecurity.net/papers/shellcode/alpha.pdf

Alphanumeric Shellcode ? Packet Storm