CVE-2016-7551 in Asterisk
Summary
by MITRE
chain_sip in Asterisk Open Source 11.x before 11.23.1 and 13.x 13.11.1 and Certified Asterisk 11.6 before 11.6-cert15 and 13.8 before 13.8-cert3 allows remote attackers to cause a denial of service (port exhaustion).
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Analysis
by VulDB Data Team • 12/17/2019
The vulnerability identified as CVE-2016-7551 affects Asterisk Open Source and Certified Asterisk versions prior to specific patches, representing a critical denial of service flaw that can exhaust system resources through improper handling of SIP (Session Initiation Protocol) messages. This vulnerability specifically impacts the chain_sip functionality within the Asterisk telephony platform, which is widely used for voice over IP communications in enterprise and service provider environments. The flaw enables remote attackers to exploit the system by sending malformed or specially crafted SIP messages that trigger excessive port allocation and connection handling, ultimately leading to resource exhaustion that prevents legitimate users from establishing connections.
The technical root cause of this vulnerability lies in the insufficient validation and resource management within the SIP channel driver implementation. When processing incoming SIP messages through the chain_sip function, the system fails to properly limit the number of concurrent connections or properly clean up resources associated with failed connection attempts. This weakness creates a condition where an attacker can repeatedly initiate SIP registration or call setup requests that consume system ports and memory resources without adequate cleanup or rate limiting. The vulnerability is classified as a resource exhaustion issue that can be exploited remotely, making it particularly dangerous in networked environments where unauthorized users might access the system through exposed SIP ports.
The operational impact of this vulnerability extends beyond simple service disruption, as it can severely compromise the availability of telephony services in organizations relying on Asterisk for their communication infrastructure. When exploited successfully, the vulnerability can cause the target system to exhaust its available ports, making it impossible for legitimate users to establish new SIP connections or register devices. This can result in complete communication outages for businesses, call centers, or service providers that depend on Asterisk for their VoIP operations. The vulnerability is particularly concerning because it can be exploited without authentication, meaning that any remote attacker with network access to the affected system can potentially trigger the denial of service condition. Network monitoring systems may not immediately detect this attack as it appears as normal SIP traffic, making it difficult to identify and mitigate.
Organizations should implement immediate mitigations including applying the relevant security patches released by Asterisk for versions 11.23.1 and 13.11.1, as well as the certified versions 11.6-cert15 and 13.8-cert3. Network-level protections such as rate limiting on SIP ports, firewall rules restricting access to SIP endpoints, and implementing SIP-specific intrusion detection systems can provide additional defense in depth. The vulnerability aligns with CWE-400, which covers resource exhaustion issues, and can be mapped to ATT&CK technique T1499.004 for network denial of service attacks. System administrators should also consider implementing monitoring for unusual port usage patterns and SIP registration spikes that could indicate exploitation attempts. Regular security assessments of telephony infrastructure and maintaining updated threat intelligence regarding SIP-based attacks are essential practices to prevent successful exploitation of this vulnerability.