CVE-2016-2316 in Asterisk
Summary
by MITRE
chan_sip in Asterisk Open Source 1.8.x, 11.x before 11.21.1, 12.x, and 13.x before 13.7.1 and Certified Asterisk 1.8.28, 11.6 before 11.6-cert12, and 13.1 before 13.1-cert3, when the timert1 sip.conf configuration is set to a value greater than 1245, allows remote attackers to cause a denial of service (file descriptor consumption) via vectors related to large retransmit timeout values.
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Analysis
by VulDB Data Team • 07/08/2022
The vulnerability identified as CVE-2016-2316 affects the chan_sip channel driver within Asterisk Open Source and Certified Asterisk implementations across multiple version ranges. This issue specifically targets the SIP protocol handling mechanism that manages retransmission timeouts for SIP signaling messages. The flaw manifests when the timert1 parameter in the sip.conf configuration file is set to values exceeding 1245 milliseconds, creating a condition that can be exploited by remote attackers to consume excessive system resources. The vulnerability represents a classic resource exhaustion attack vector that can lead to system instability and service disruption.
The technical root cause of this vulnerability lies in the improper handling of large retransmit timeout values within the SIP channel driver's internal state management. When timert1 exceeds the threshold of 1245 milliseconds, the system's retransmission logic begins to consume file descriptors at an accelerated rate without proper bounds checking or resource limitation mechanisms. This behavior creates a cascading effect where the system's file descriptor table becomes saturated, leading to denial of service conditions that prevent legitimate SIP signaling operations from functioning properly. The vulnerability maps to CWE-400, which specifically addresses unchecked resource consumption, and aligns with ATT&CK technique T1499.004 for network denial of service attacks.
The operational impact of this vulnerability extends beyond simple service disruption to encompass broader system stability concerns within telephony environments. Attackers can leverage this weakness to systematically consume available file descriptors, causing legitimate SIP endpoints to fail in establishing or maintaining connections. This creates a scenario where authorized users experience connection failures while the system gradually degrades into a non-functional state. The vulnerability affects both the open source Asterisk distributions and the certified versions, indicating it exists at a fundamental level within the SIP channel driver implementation. Organizations utilizing Asterisk for voice communications face significant risk of service interruption, particularly in environments where SIP signaling traffic is high and the system's resource management is not properly monitored.
Mitigation strategies for CVE-2016-2316 should focus on immediate configuration changes and system hardening measures. The most effective immediate solution involves setting the timert1 parameter in sip.conf to values below the problematic threshold of 1245 milliseconds, typically recommending values between 1000 and 1500 milliseconds for most operational environments. System administrators should implement monitoring solutions to track file descriptor usage and establish alerting mechanisms when consumption approaches critical thresholds. Additionally, organizations should apply the relevant security patches provided by Asterisk for their specific version ranges, ensuring that all systems are updated to versions that address this specific resource management flaw. Network segmentation and access control measures can provide additional defense in depth, limiting the attack surface available to potential remote adversaries. The vulnerability demonstrates the critical importance of proper resource management in telephony systems and highlights the need for comprehensive security testing of protocol implementations.