CVE-2013-5641 in Asterisk
Summary
by MITRE
The SIP channel driver (channels/chan_sip.c) in Asterisk Open Source 1.8.17.x through 1.8.22.x, 1.8.23.x before 1.8.23.1, and 11.x before 11.5.1 and Certified Asterisk 1.8.15 before 1.8.15-cert3 and 11.2 before 11.2-cert2 allows remote attackers to cause a denial of service (NULL pointer dereference, segmentation fault, and daemon crash) via an ACK with SDP to a previously terminated channel. NOTE: some of these details are obtained from third party information.
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Analysis
by VulDB Data Team • 05/21/2021
The vulnerability identified as CVE-2013-5641 affects the Session Initiation Protocol (SIP) channel driver within Asterisk Open Source and Certified Asterisk implementations. This issue manifests in multiple version ranges including 1.8.17.x through 1.8.22.x, 1.8.23.x before 1.8.23.1, 11.x before 11.5.1, and specific certified versions. The flaw represents a critical security weakness that enables remote attackers to disrupt service availability through carefully crafted SIP packets. The vulnerability specifically targets the handling of ACK messages containing Session Description Protocol (SDP) data, which are typically used to confirm successful session establishment in SIP communications.
The technical mechanism behind this vulnerability involves a NULL pointer dereference condition that occurs when the SIP channel driver processes an ACK message containing SDP information sent to a channel that has already been terminated. This particular scenario exploits a race condition or improper state management within the Asterisk signaling engine where the system attempts to access memory locations that have already been freed or are not properly initialized. When the daemon encounters this malformed packet sequence, it triggers a segmentation fault leading to an immediate crash of the Asterisk process. The underlying cause can be classified as a CWE-476: NULL Pointer Dereference, which represents a fundamental programming error where software attempts to access memory through a pointer that has not been properly initialized.
The operational impact of this vulnerability extends beyond simple service disruption to potentially enable broader attack scenarios within telephony infrastructure environments. A remote attacker can exploit this weakness to repeatedly crash the Asterisk daemon, resulting in persistent denial of service conditions that can severely impact business communications, VoIP services, and unified communications systems. The vulnerability is particularly concerning because it requires minimal privileges to exploit, as attackers only need to send specially crafted SIP packets to the target system without authentication. This makes the attack surface extremely broad, affecting any organization running vulnerable Asterisk versions in their telephony infrastructure, whether in enterprise environments, service provider networks, or small business deployments.
Organizations should implement immediate mitigations including applying the vendor-provided patches and updates for affected versions, as well as implementing network-level controls such as firewalls that can filter out suspicious SIP traffic patterns. The ATT&CK framework categorizes this vulnerability under T1499.004: Endpoint Denial of Service, specifically targeting network services through malformed packet delivery. Additionally, network segmentation strategies should be employed to limit exposure of critical telephony infrastructure, while monitoring systems should be configured to detect unusual patterns of service disruptions or daemon restarts. Organizations should also consider implementing intrusion detection systems that can identify and alert on potential exploitation attempts targeting this specific vulnerability pattern, as the attack vector is relatively simple and can be automated for large-scale impact.