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Asterisk DoS Vulnerability (AST-2021-005)

Information

Severity

Severity

High

Family

Family

Denial of Service

CVSSv2 Base

CVSSv2 Base

7.8

CVSSv2 Vector

CVSSv2 Vector

AV:N/AC:L/Au:N/C:N/I:N/A:C

Solution Type

Solution Type

Vendor Patch

Created

Created

1 year ago

Modified

Modified

1 year ago

Summary

Asterisk is prone to a denial of service vulnerability in the PJSIP channel driver.

Insight

Insight

Given a scenario where an outgoing call is placed from Asterisk to a remote SIP server it is possible for a crash to occur. The code responsible for negotiating SDP in SIP responses incorrectly assumes that SDP negotiation will always be successful. If a SIP response containing an SDP that can not be negotiated is received a subsequent SDP negotiation on the same call can cause a crash. If the 'accept_multiple_sdp_answers' option in the 'system' section of pjsip.conf is set to 'yes' then any subsequent non-forked SIP response with SDP can trigger this crash. If the 'follow_early_media_fork' option in the 'system' section of pjsip.conf is set to 'yes' (the default) then any subsequent SIP responses with SDP from a forked destination can trigger this crash. If a 200 OK with SDP is received from a forked destination it can also trigger this crash, even if the 'follow_early_media_fork' option is not set to 'yes'. In all cases this relies on a race condition with tight timing where the second SDP negotiation occurs before termination of the call due to the initial SDP negotiation failure.

Affected Software

Affected Software

Asterisk Open Source 13.x, 16.x, 17.x, 18.x and 16.x Certified Asterisk.

Detection Method

Detection Method

Checks if a vulnerable version is present on the target host.

Solution

Solution

Update to version 13.38.2, 16.16.1, 17.9.2, 18.2.1, 16.8-cert6 or later.

Common Vulnerabilities and Exposures (CVE)

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1. Download Multipass

sudo snap install multipass

2. Launch a multipass instance

multipass launch -c 2 -m 6G -d 20G -n mageni 20.04 && multipass shell mageni

3. Install Mageni

curl -sL https://www.mageni.net/installation | sudo bash

1. If you don’t have it already, install Brew. Then, to install Multipass simply execute:

brew install --cask multipass

2. Launch a multipass instance

multipass launch -c 2 -m 6G -d 20G -n mageni 20.04 && multipass shell mageni

2. Install Mageni

curl -sL https://www.mageni.net/installation | sudo bash

1. Download the installer for Windows

Note: You need Windows 10 Pro/Enterprise/Education v 1803 or later, or any Windows 10 with VirtualBox

2. Ensure your network is private

Make sure your local network is designated as private, otherwise Windows prevents Multipass from starting.

3. Run the installer

You need to allow the installer to gain Administrator privileges.

4. Launch a multipass instance

multipass launch -c 2 -m 6G -d 20G -n mageni 20.04

5. Log into the multipass instance

multipass shell mageni

6. Install Mageni

curl -sL https://www.mageni.net/installation | sudo bash