Search results
Results from the WOW.Com Content Network
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. For example, on the IA-32 architecture one could replace this instruction:
Set all bytes in a block of memory to a given byte value. Base instruction 0xFE 0x15 initobj <typeTok> Initialize the value at address dest. Object model instruction 0x75 isinst <class> Test if obj is an instance of class, returning null or an instance of that class or interface. Object model instruction 0x27 jmp <method>
While this method prevents the canonical stack smashing exploit, stack overflows can be exploited in other ways. First, it is common to find ways to store shellcode in unprotected memory regions like the heap, and so very little need change in the way of exploitation. [12] Another attack is the so-called return to libc method for shellcode ...
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
Address space layout randomization (ASLR) is a computer security technique involved in preventing exploitation of memory corruption vulnerabilities. [1] In order to prevent an attacker from reliably redirecting code execution to, for example, a particular exploited function in memory, ASLR randomly arranges the address space positions of key data areas of a process, including the base of the ...
Visualization of a software buffer overflow. Data is written into A, but is too large to fit within A, so it overflows into B.. In programming and information security, a buffer overflow or buffer overrun is an anomaly whereby a program writes data to a buffer beyond the buffer's allocated memory, overwriting adjacent memory locations.
In all modern character sets, the null character has a code point value of zero. In most encodings, this is translated to a single code unit with a zero value. For instance, in UTF-8 it is a single zero byte. However, in Modified UTF-8 the null character is encoded as two bytes : 0xC0,0x80. This allows the byte with the value of zero, which is ...
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 ...