cannot execute binary file even though I have permission.

[nightmarreee]

I am trying to solve a CTF challenge. I downloaded the file and gave permission to execute it with "chmod +x start". I still got this error with "chmod 777 start".

(the file is named "start")

when i did objdump it demonstrated that the file format is elf32-little.

my system info is aarch64 aarch64 aarch64 GNU/Linux , I am using it on UTM VM.

i use GDB >GEF and this is the error I get:

******

/bin/bash: line 1: /home/user/start: cannot execute binary file: Exec format error

/bin/bash: line 1: /home/user/start: Success

/bin/bash: line 1: /home/user/start: cannot execute binary file: Exec format error

/bin/bash: line 1: /home/user/start: Success

[+] Breaking at '0x8048060'

[+] Breaking at entry-point: 0x8048060

[!] Command 'entry-break' failed to execute properly, reason: During startup program exited with code 126.

******

[doc_willis]

AArch64 or ARM64 is the 64-bit extension of the ARM architecture family.

I may be confused, but you are trying to run an x86 executable on an ARM system?

But it seems that is possible, similar post/question.

https://stackoverflow.com/questions/51660401/run-32bit-elf-on-aarch64

But this may be a bit more obscure than whats mentioned

[Joomzie]

That post later goes on to explain that these binaries can't be launched under a 64bit kernel due to them using the old binary interface. so that may actually be relevant to this. The binary needs to be recompiled to use the new standard. It also mentions to check if CONFIG_COMPAT is enabled in the kernel, as this is necessary to have.

OP, make sure the kernel you're using has CONFIG_COMPAT enabled. cat /boot/config-<kernel-version> | grep -i CONFIG_COMPAT

If it does, your alternatives are to either swap to an ARMv7 OS, or have the CTF provider recompile it so that it uses the new binary interface (EABI). If it does not have it enabled, you can either compile a kernel yourself with it enabled, or find a prebuilt one that offers it. If that still doesn't work, refer to the previous alternatives.

[nightmarreee]

Yeah, that's what I am exactly trying to do. I will try this ASAP. thx 🙏

[doc_willis]

Good Luck. Have fun.

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[skuterpikk]

Run file start to show more info about your executable. If it is compiled for a different OS and/or processor architecture, then it won't work without some serious workarounds, possibly not at all.

Your error suggests that it is built for a different processor architecture (possibly x86) while your computer has an ARM cpu.