CVE-2017-7617 in Asterisk
Summary
by MITRE
Remote code execution can occur in Asterisk Open Source 13.x before 13.14.1 and 14.x before 14.3.1 and Certified Asterisk 13.13 before 13.13-cert3 because of a buffer overflow in a CDR user field, related to X-ClientCode in chan_sip, the CDR dialplan function, and the AMI Monitor action.
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Analysis
by VulDB Data Team • 12/17/2019
The vulnerability identified as CVE-2017-7617 represents a critical buffer overflow condition affecting Asterisk Open Source versions 13.x prior to 13.14.1 and 14.x prior to 14.3.1, along with Certified Asterisk 13.13 versions before 13.13-cert3. This flaw exists within the Call Detail Record (CDR) processing mechanism and specifically impacts the X-ClientCode header handling within the chan_sip channel driver. The vulnerability arises from insufficient input validation when processing CDR user fields, creating an exploitable condition that allows remote attackers to execute arbitrary code on affected systems. The buffer overflow occurs during the processing of SIP messages that contain specially crafted X-ClientCode values, which are then passed through the CDR dialplan function and subsequently handled by the AMI Monitor action. This vulnerability falls under CWE-121, which describes stack-based buffer overflow conditions, and represents a classic example of how improper input handling can lead to remote code execution. The attack vector is particularly concerning as it enables remote exploitation without requiring authentication, making it accessible to any attacker who can send SIP messages to the targeted Asterisk server.
The technical exploitation of this vulnerability leverages the interaction between multiple Asterisk components including the SIP channel driver, CDR subsystem, and the Asterisk Manager Interface. When a malicious SIP message containing an oversized X-ClientCode header is received, the buffer overflow occurs during the CDR generation process, specifically when the system attempts to store the user-defined field data in a fixed-size buffer. The AMI Monitor action, which provides real-time monitoring capabilities through the Asterisk Manager Interface, creates an additional attack surface by processing the malformed CDR data, potentially allowing attackers to inject malicious code into the system memory. This vulnerability is particularly dangerous because it can be triggered through legitimate SIP communication channels, making detection difficult and allowing attackers to maintain persistence within the network infrastructure. The exploitability of this condition is enhanced by the fact that it operates at the application layer and requires no special privileges or authentication, aligning with ATT&CK technique T1059.007 for command and scripting interpreter.
The operational impact of CVE-2017-7617 extends beyond simple remote code execution to encompass complete system compromise and potential network infiltration. Successful exploitation can result in full control of the Asterisk server, enabling attackers to access sensitive telephony data, intercept communications, modify call routing, and potentially use the compromised system as a pivot point for attacking other network resources. The vulnerability affects organizations relying on Asterisk for voice communication services, including telecommunications providers, enterprise PBX systems, and VoIP infrastructure deployments. Organizations utilizing these vulnerable versions face significant risk of unauthorized access to their telephony infrastructure, potentially leading to service disruption, data breaches, and compliance violations. The vulnerability's impact is amplified in environments where Asterisk systems are directly exposed to the internet or where insufficient network segmentation exists between telephony infrastructure and critical business systems. Security professionals should note that this vulnerability demonstrates the importance of input validation in telephony systems and highlights the need for comprehensive security testing of communication protocols. The attack surface for this vulnerability includes not only the direct SIP communication channels but also any system components that interact with the affected CDR processing functions, making it a comprehensive threat to telephony infrastructure security.
Organizations should implement immediate mitigations including applying the vendor-provided patches and updates for Asterisk versions 13.14.1 and 14.3.1, along with Certified Asterisk 13.13-cert3 releases. Network segmentation should be implemented to isolate Asterisk servers from critical network segments, and access controls should be enforced to limit SIP communication to trusted sources only. Monitoring should be enhanced to detect unusual patterns in SIP message headers and CDR generation activities, with particular attention to X-ClientCode field values. The implementation of intrusion detection systems capable of identifying malicious SIP traffic patterns can provide early warning of exploitation attempts. Additionally, organizations should conduct comprehensive security assessments of their telephony infrastructure to identify any other potential vulnerabilities in related components and ensure that all telephony services are running on patched and supported versions of Asterisk. System hardening measures including disabling unnecessary SIP features and implementing proper input validation at all communication interfaces will further reduce the risk of exploitation. Regular security updates and vulnerability assessments should be maintained as part of the overall security posture to prevent similar issues from arising in the future, particularly given the critical nature of telephony infrastructure in business communications.