Test ID:	1.3.6.1.4.1.25623.1.0.145420
Category:	Denial of Service
Title:	Asterisk DoS Vulnerability (AST-2021-005)
Summary:	Asterisk is prone to a denial of service vulnerability in the; PJSIP channel driver.
Description:	Summary: Asterisk is prone to a denial of service vulnerability in the PJSIP channel driver. Vulnerability 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/OS: Asterisk Open Source 13.x, 16.x, 17.x, 18.x and 16.x Certified Asterisk. Solution: Update to version 13.38.2, 16.16.1, 17.9.2, 18.2.1, 16.8-cert6 or later. CVSS Score: 4.3 CVSS Vector: AV:N/AC:M/Au:N/C:N/I:N/A:P
Cross-Ref:	Common Vulnerability Exposure (CVE) ID: CVE-2021-26906 http://seclists.org/fulldisclosure/2021/Feb/61 http://packetstormsecurity.com/files/161477/Asterisk-Project-Security-Advisory-AST-2021-005.html https://downloads.asterisk.org/pub/security/
Copyright	Copyright (C) 2021 Greenbone AG

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