1
2 /***************************************************************************
3 * ncrack_telnet.cc -- ncrack module for the TELNET protocol *
4 * *
5 ***********************IMPORTANT NMAP LICENSE TERMS************************
6 * *
7 * The Nmap Security Scanner is (C) 1996-2019 Insecure.Com LLC ("The Nmap *
8 * Project"). Nmap is also a registered trademark of the Nmap Project. *
9 * This program is free software; you may redistribute and/or modify it *
10 * under the terms of the GNU General Public License as published by the *
11 * Free Software Foundation; Version 2 ("GPL"), BUT ONLY WITH ALL OF THE *
12 * CLARIFICATIONS AND EXCEPTIONS DESCRIBED HEREIN. This guarantees your *
13 * right to use, modify, and redistribute this software under certain *
14 * conditions. If you wish to embed Nmap technology into proprietary *
15 * software, we sell alternative licenses (contact sales@nmap.com). *
16 * Dozens of software vendors already license Nmap technology such as *
17 * host discovery, port scanning, OS detection, version detection, and *
18 * the Nmap Scripting Engine. *
19 * *
20 * Note that the GPL places important restrictions on "derivative works", *
21 * yet it does not provide a detailed definition of that term. To avoid *
22 * misunderstandings, we interpret that term as broadly as copyright law *
23 * allows. For example, we consider an application to constitute a *
24 * derivative work for the purpose of this license if it does any of the *
25 * following with any software or content covered by this license *
26 * ("Covered Software"): *
27 * *
28 * o Integrates source code from Covered Software. *
29 * *
30 * o Reads or includes copyrighted data files, such as Nmap's nmap-os-db *
31 * or nmap-service-probes. *
32 * *
33 * o Is designed specifically to execute Covered Software and parse the *
34 * results (as opposed to typical shell or execution-menu apps, which will *
35 * execute anything you tell them to). *
36 * *
37 * o Includes Covered Software in a proprietary executable installer. The *
38 * installers produced by InstallShield are an example of this. Including *
39 * Nmap with other software in compressed or archival form does not *
40 * trigger this provision, provided appropriate open source decompression *
41 * or de-archiving software is widely available for no charge. For the *
42 * purposes of this license, an installer is considered to include Covered *
43 * Software even if it actually retrieves a copy of Covered Software from *
44 * another source during runtime (such as by downloading it from the *
45 * Internet). *
46 * *
47 * o Links (statically or dynamically) to a library which does any of the *
48 * above. *
49 * *
50 * o Executes a helper program, module, or script to do any of the above. *
51 * *
52 * This list is not exclusive, but is meant to clarify our interpretation *
53 * of derived works with some common examples. Other people may interpret *
54 * the plain GPL differently, so we consider this a special exception to *
55 * the GPL that we apply to Covered Software. Works which meet any of *
56 * these conditions must conform to all of the terms of this license, *
57 * particularly including the GPL Section 3 requirements of providing *
58 * source code and allowing free redistribution of the work as a whole. *
59 * *
60 * As another special exception to the GPL terms, the Nmap Project grants *
61 * permission to link the code of this program with any version of the *
62 * OpenSSL library which is distributed under a license identical to that *
63 * listed in the included docs/licenses/OpenSSL.txt file, and distribute *
64 * linked combinations including the two. *
65 * *
66 * The Nmap Project has permission to redistribute Npcap, a packet *
67 * capturing driver and library for the Microsoft Windows platform. *
68 * Npcap is a separate work with it's own license rather than this Nmap *
69 * license. Since the Npcap license does not permit redistribution *
70 * without special permission, our Nmap Windows binary packages which *
71 * contain Npcap may not be redistributed without special permission. *
72 * *
73 * Any redistribution of Covered Software, including any derived works, *
74 * must obey and carry forward all of the terms of this license, including *
75 * obeying all GPL rules and restrictions. For example, source code of *
76 * the whole work must be provided and free redistribution must be *
77 * allowed. All GPL references to "this License", are to be treated as *
78 * including the terms and conditions of this license text as well. *
79 * *
80 * Because this license imposes special exceptions to the GPL, Covered *
81 * Work may not be combined (even as part of a larger work) with plain GPL *
82 * software. The terms, conditions, and exceptions of this license must *
83 * be included as well. This license is incompatible with some other open *
84 * source licenses as well. In some cases we can relicense portions of *
85 * Nmap or grant special permissions to use it in other open source *
86 * software. Please contact fyodor@nmap.org with any such requests. *
87 * Similarly, we don't incorporate incompatible open source software into *
88 * Covered Software without special permission from the copyright holders. *
89 * *
90 * If you have any questions about the licensing restrictions on using *
91 * Nmap in other works, we are happy to help. As mentioned above, we also *
92 * offer an alternative license to integrate Nmap into proprietary *
93 * applications and appliances. These contracts have been sold to dozens *
94 * of software vendors, and generally include a perpetual license as well *
95 * as providing support and updates. They also fund the continued *
96 * development of Nmap. Please email sales@nmap.com for further *
97 * information. *
98 * *
99 * If you have received a written license agreement or contract for *
100 * Covered Software stating terms other than these, you may choose to use *
101 * and redistribute Covered Software under those terms instead of these. *
102 * *
103 * Source is provided to this software because we believe users have a *
104 * right to know exactly what a program is going to do before they run it. *
105 * This also allows you to audit the software for security holes. *
106 * *
107 * Source code also allows you to port Nmap to new platforms, fix bugs, *
108 * and add new features. You are highly encouraged to send your changes *
109 * to the dev@nmap.org mailing list for possible incorporation into the *
110 * main distribution. By sending these changes to Fyodor or one of the *
111 * Insecure.Org development mailing lists, or checking them into the Nmap *
112 * source code repository, it is understood (unless you specify *
113 * otherwise) that you are offering the Nmap Project the unlimited, *
114 * non-exclusive right to reuse, modify, and relicense the code. Nmap *
115 * will always be available Open Source, but this is important because *
116 * the inability to relicense code has caused devastating problems for *
117 * other Free Software projects (such as KDE and NASM). We also *
118 * occasionally relicense the code to third parties as discussed above. *
119 * If you wish to specify special license conditions of your *
120 * contributions, just say so when you send them. *
121 * *
122 * This program is distributed in the hope that it will be useful, but *
123 * WITHOUT ANY WARRANTY; without even the implied warranty of *
124 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the Nmap *
125 * license file for more details (it's in a COPYING file included with *
126 * Nmap, and also available from https://svn.nmap.org/nmap/COPYING) *
127 * *
128 ***************************************************************************/
129
130
131 #include "ncrack.h"
132 #include "nsock.h"
133 #include "NcrackOps.h"
134 #include "Service.h"
135 #include "modules.h"
136 #include <list>
137
138
139 /* Telnet Commands */
140 #define IAC 255 /* interpret as command: */
141 #define DONT 254 /* you are not to use option */
142 #define DO 253 /* please, you use option */
143 #define WONT 252 /* I won't use option */
144 #define WILL 251 /* I will use option */
145 #define SB 250 /* interpret as subnegotiation */
146 #define SE 240 /* end sub negotiation */
147
148 /* Telnet Options */
149 #define LINEMODE 34
150
151 #define WILL_LINEMODE "\xff\xfb\x22"
152 #define DO_LINEMODE "\xff\xfd\x22"
153
154
155 extern NcrackOps o;
156
157 extern void ncrack_read_handler(nsock_pool nsp, nsock_event nse, void *mydata);
158 extern void ncrack_write_handler(nsock_pool nsp, nsock_event nse, void *mydata);
159 extern void ncrack_timer_handler(nsock_pool nsp, nsock_event nse, void *mydata);
160 extern void ncrack_module_end(nsock_pool nsp, void *mydata);
161
162 typedef struct telnet_info {
163 bool linemode; /* true if peer supports linemode */
164 /* Some devices don't even bother to answer our question of whether they
165 * support linemode or not, and thus we need a separate boolean to tell us
166 * if we sent a request, so we can try only once.
167 */
168 bool asked_for_linemode;
169 bool linemode_not_supported; /* peer told us that he doesn't support linemode */
170 bool can_start_auth;
171 char *userptr;
172 char *passptr;
173 } telnet_info;
174
175
176 enum states { TELNET_INIT, TELNET_OPTIONS_1, TELNET_OPTIONS_2, TELNET_AUTH, TELNET_ECHO_USER,
177 TELNET_PASS_R, TELNET_PASS_W, TELNET_FINI };
178
179 void
ncrack_telnet(nsock_pool nsp,Connection * con)180 ncrack_telnet(nsock_pool nsp, Connection *con)
181 {
182 char lbuf[BUFSIZE]; /* local buffer */
183 /* We can't let nsock handle the size by looking at '\0'
184 * because telnet uses 0 as a valid value for options
185 * (e.g binary transmission option) */
186 size_t lbufsize;
187 nsock_iod nsi = con->niod;
188 telnet_info *info = NULL;
189 size_t datasize;
190 char *recvbufptr = NULL;
191 size_t recvbuflen = 0;
192 char *localbufptr = lbuf;
193 if (con->misc_info)
194 info = (telnet_info *) con->misc_info;
195
196 switch (con->state)
197 {
198 case TELNET_INIT:
199 con->peer_might_close = false;
200 con->misc_info = (telnet_info *)safe_zalloc(sizeof(telnet_info));
201 con->state = TELNET_OPTIONS_1;
202 nsock_read(nsp, nsi, ncrack_read_handler, 50000, con);
203 break;
204
205 case TELNET_OPTIONS_1:
206
207 recvbufptr = (char *)con->inbuf->get_dataptr();
208 recvbuflen = con->inbuf->get_len();
209
210 /* Telnet Option Parsing */
211 while (*recvbufptr == (char) IAC
212 && ((size_t)(recvbufptr - (char *)con->inbuf->get_dataptr()) < recvbuflen)
213 && ((localbufptr - lbuf) < BUFSIZE - 3)) {
214
215 /* For every option other than linemode we reject it */
216 if (recvbufptr[1] == (char) WILL) {
217 if (recvbufptr[2] == (char) LINEMODE) {
218 /* reply is needed only when we haven't asked explicitly if the peer
219 * supports linemode itself
220 */
221 if (info->asked_for_linemode == false) {
222 memcpy(localbufptr, WILL_LINEMODE, sizeof(WILL_LINEMODE));
223 localbufptr += 3;
224 }
225 info->linemode = true;
226 } else {
227 snprintf(localbufptr, 4, "%c%c%c", IAC, DONT, recvbufptr[2]);
228 localbufptr += 3;
229 }
230 recvbufptr += 3;
231
232 } else if (recvbufptr[1] == (char) WONT) {
233 if (recvbufptr[2] == LINEMODE) {
234 info->linemode = false;
235 info->linemode_not_supported = true;
236 } else {
237 snprintf(localbufptr, 4, "%c%c%c", IAC, DONT, recvbufptr[2]);
238 localbufptr += 3;
239 }
240 recvbufptr += 3;
241
242 } else if (recvbufptr[1] == (char) DONT) {
243 if (recvbufptr[2] == LINEMODE) {
244 info->linemode = false;
245 info->linemode_not_supported = true;
246 }
247 snprintf(localbufptr, 4, "%c%c%c", IAC, WONT, recvbufptr[2]);
248 localbufptr += 3;
249 recvbufptr += 3;
250
251 } else if (recvbufptr[1] == (char) DO) {
252 if (recvbufptr[2] == LINEMODE) {
253 if (info->asked_for_linemode == false) {
254 memcpy(localbufptr, WILL_LINEMODE, sizeof(WILL_LINEMODE));
255 localbufptr += 3;
256 }
257 info->linemode = true;
258 } else {
259 snprintf(localbufptr, 4, "%c%c%c", IAC, WONT, recvbufptr[2]);
260 localbufptr += 3;
261 }
262 recvbufptr += 3;
263
264 /* We just ignore any suboption we receive */
265 } else if (recvbufptr[1] == (char) SB) {
266 while (*recvbufptr != (char) SE
267 && (size_t)((recvbufptr - (char *)con->inbuf->get_dataptr())) < recvbuflen)
268 recvbufptr++;
269 recvbufptr++;
270 }
271 }
272
273 /* If peer didn't sent linemode as part of its options and didn't sent a
274 * command saying he doesn't support it and this is the first time we
275 * request it from him, then try to ask him explicitly if
276 * he supports it.
277 */
278 if (info->linemode == false
279 && info->linemode_not_supported == false
280 && info->asked_for_linemode == false) {
281 if ((localbufptr - lbuf) < BUFSIZE - 3) {
282 memcpy(localbufptr, WILL_LINEMODE, sizeof(WILL_LINEMODE));
283 info->asked_for_linemode = true;
284 localbufptr += 3;
285 }
286 }
287
288 datasize = recvbuflen - (recvbufptr - (char *)con->inbuf->get_dataptr());
289
290 /* Now check for banner and login prompt */
291 if (datasize > 0) {
292 if (o.debugging > 8) {
293 //memprint(recvbufptr, datasize);
294 //printf("\n");
295 }
296 /* If we see a certain pattern that denotes that we can start
297 * authentication then we note that down. */
298 if (memsearch(recvbufptr, "login", datasize)
299 || memsearch(recvbufptr, "username", datasize))
300 info->can_start_auth = true;
301 }
302
303 lbufsize = localbufptr - lbuf;
304
305 con->state = TELNET_OPTIONS_2;
306 /* If we have something to send then do so. Else just wait until you
307 * receive a relevant authentication pattern to start cracking.
308 */
309 if (localbufptr != lbuf) {
310 nsock_write(nsp, nsi, ncrack_write_handler, 10000, con, lbuf, lbufsize);
311 } else {
312 if (info->can_start_auth == true)
313 con->state = TELNET_AUTH;
314 /* That's a bit of a hack, but we need the module to be called again
315 * with a changed state without issuing a read or write this time. And
316 * thus we create a timer event with a timeout of 0 milliseconds */
317 nsock_timer_create(nsp, ncrack_timer_handler, 0, con);
318 }
319 break;
320
321 case TELNET_OPTIONS_2:
322 delete con->inbuf;
323 con->inbuf = NULL;
324
325 con->state = TELNET_OPTIONS_1;
326 nsock_read(nsp, nsi, ncrack_read_handler, 10000, con);
327 break;
328
329 case TELNET_AUTH:
330 if (info->linemode) {
331 con->state = TELNET_PASS_R;
332 snprintf(lbuf, sizeof(lbuf), "%s\r", con->user);
333 nsock_write(nsp, nsi, ncrack_write_handler, 10000, con, lbuf, -1);
334 } else {
335 con->state = TELNET_ECHO_USER;
336 /* Since our peer doesn't support linemode, we need to send each
337 * character of the username in individual packets. We send 1 byte
338 * and wait for the server's echo and so on...
339 */
340 if (con->inbuf) {
341 recvbufptr = (char *)con->inbuf->get_dataptr();
342 recvbuflen = con->inbuf->get_len();
343 }
344
345 if (!info->userptr)
346 info->userptr = con->user;
347
348 /* OK, here's the deal: we need to account for the fact that some
349 * telnet daemons (hint: cisco routers) send the initial login prompt
350 * and then start sending telnet options. Since we have already, sent
351 * the first username character by now, we will just have to ignore
352 * those options, and wait until we see our character echoed back in
353 * order to go on sending the rest of the username.
354 */
355 if (con->inbuf && info->userptr > con->user
356 && (size_t)((info->userptr - con->user)) != strlen(con->user)) {
357 /* Some telnet daemons send the echo reply with a \0 byte in front of
358 * the echoed characted. Damn inconsistencies. */
359 if ((recvbuflen > 2 && recvbufptr[1] != *(info->userptr - 1))
360 || (recvbuflen == 1 && recvbufptr[0] != *(info->userptr - 1))) {
361 nsock_timer_create(nsp, ncrack_timer_handler, 0, con);
362 break;
363 }
364 }
365
366 /* we can move on to reading the password prompt */
367 if (recvbufptr && info->userptr > con->user &&
368 memsearch(recvbufptr, "\r", recvbuflen)) {
369 if (memsearch(recvbufptr, "password", recvbuflen))
370 con->state = TELNET_PASS_W;
371 else
372 con->state = TELNET_PASS_R;
373 nsock_timer_create(nsp, ncrack_timer_handler, 0, con);
374 break;
375 }
376
377 if ((size_t)(info->userptr - con->user) == strlen(con->user)) {
378 lbuf[0] = '\r';
379 lbuf[1] = '\0';
380 nsock_write(nsp, nsi, ncrack_write_handler, 10000, con, lbuf, 2);
381 } else {
382 lbuf[0] = info->userptr[0];
383 info->userptr++;
384 nsock_write(nsp, nsi, ncrack_write_handler, 10000, con, lbuf, 1);
385 }
386 }
387 break;
388
389 case TELNET_ECHO_USER:
390 delete con->inbuf;
391 con->inbuf = NULL;
392
393 con->state = TELNET_AUTH;
394 nsock_read(nsp, nsi, ncrack_read_handler, 10000, con);
395 break;
396
397 case TELNET_PASS_R:
398 delete con->inbuf;
399 con->inbuf = NULL;
400
401 con->state = TELNET_PASS_W;
402 nsock_read(nsp, nsi, ncrack_read_handler, 10000, con);
403 break;
404
405 case TELNET_PASS_W:
406 /* After some testing, it seems that we can send the password
407 * as one packet, even if linemode is disabled. */
408 con->state = TELNET_FINI;
409 snprintf(lbuf, sizeof(lbuf), "%s\r", con->pass);
410 con->peer_might_close = true;
411 nsock_write(nsp, nsi, ncrack_write_handler, 10000, con, lbuf, -1);
412 break;
413
414 case TELNET_FINI:
415 if (con->inbuf) {
416 recvbufptr = (char *)con->inbuf->get_dataptr();
417 recvbuflen = con->inbuf->get_len();
418 }
419
420 if (memsearch(recvbufptr, "incorrect", recvbuflen)
421 || memsearch(recvbufptr, "fail", recvbuflen)) {
422 con->auth_success = false;
423 con->state = TELNET_AUTH;
424 info->userptr = NULL;
425 info->passptr = NULL;
426 con->peer_might_close = false;
427
428 /*
429 * If telnetd sent the final answer along with the new login prompt
430 * (something which happens with some daemons), then we don't need to
431 * check if the peer has closed the connection because obviously he hasn't!
432 */
433 if (memsearch(recvbufptr, "login", recvbuflen)
434 || memsearch(recvbufptr, "username", recvbuflen))
435 con->peer_alive = true;
436
437 delete con->inbuf;
438 con->inbuf = NULL;
439
440 return ncrack_module_end(nsp, con);
441
442 } else if (memsearch(recvbufptr, ">", recvbuflen)
443 || memsearch(recvbufptr, "$", recvbuflen)
444 || memsearch(recvbufptr, "#", recvbuflen)) {
445 con->auth_success = true;
446
447 delete con->inbuf;
448 con->inbuf = NULL;
449
450 return ncrack_module_end(nsp, con);
451
452 } else { /* wait for more replies */
453
454 delete con->inbuf;
455 con->inbuf = NULL;
456
457 con->state = TELNET_FINI;
458 nsock_read(nsp, nsi, ncrack_read_handler, 10000, con);
459 }
460 }
461
462 }
463
464