Turn on the Non-executable Stack Protection Operating systems used to allow executable stacks, but this has now changed: In Ubuntu OS, the binary images of programs (and shared libraries) must declare whether they require executable stacks or not, i.e., they need to mark a field in the program header. Kernel or dynamic linker uses this marking to decide whether to make the stack of this running program executable or non-executable. This marking is done automatically by the gcc, which by default makes stack non-executable. We can specifically make it nonexecutable using the "-z noexecstack" flag in the compilation. In our previous tasks, we used "-z execstack" to make stacks executable. In this task, we will make the stack non-executable. We will do this experiment in the shellcode folder. The callshellcode program puts a copy of shellcode on the stack, and then executes the code from the stack. Please recompile call shellcode.c into a32.out and a64.out, without the "-z execstack" option. Run them, describe and explain your observations. Defeating the non-executable stack countermeasure. It should be noted that non-executable stack only makes it impossible to run shellcode on the stack, but it does not prevent buffer-overflow attacks, because there are other ways to run malicious code after exploiting a buffer-overflow vulnerability. The return-tolibc attack is an example. We have designed a separate lab for that attack. If you are interested, please see our Return-to-Libc Attack Lab for details.
Turn on the Non-executable Stack Protection
In this task, we will make the stack non-executable. We will do this experiment in the shellcode folder. The callshellcode program puts a copy of shellcode on the stack, and then executes the code from the stack. Please recompile call shellcode.c into a32.out and a64.out, without the "-z execstack" option. Run them, describe and explain your observations.
Defeating the non-executable stack countermeasure. It should be noted that non-executable stack only makes it impossible to run shellcode on the stack, but it does not prevent buffer-overflow attacks, because there are other ways to run malicious code after exploiting a buffer-overflow vulnerability. The return-tolibc attack is an example. We have designed a separate lab for that attack. If you are interested, please see our Return-to-Libc Attack Lab for details.
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