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Asterisk DoS Vulnerability (AST-2021-005)
Information
Severity
Severity
Family
Family
CVSSv2 Base
CVSSv2 Base
CVSSv2 Vector
CVSSv2 Vector
Solution Type
Solution Type
Created
Created
Modified
Modified
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.