CVE-2018-17281 in PBX
Summary
by MITRE
There is a stack consumption vulnerability in the res_http_websocket.so module of Asterisk through 13.23.0, 14.7.x through 14.7.7, and 15.x through 15.6.0 and Certified Asterisk through 13.21-cert2. It allows an attacker to crash Asterisk via a specially crafted HTTP request to upgrade the connection to a websocket.
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Analysis
by VulDB Data Team • 05/17/2023
The vulnerability identified as CVE-2018-17281 represents a critical stack consumption flaw within the Asterisk telephony platform's res_http_websocket.so module. This issue affects multiple versions of the open-source PBX system including Asterisk 13.23.0 and earlier, 14.7.x versions through 14.7.7, 15.x versions through 15.6.0, and the certified Asterisk 13.21-cert2 release. The vulnerability specifically targets the HTTP to WebSocket upgrade mechanism, making it particularly dangerous for systems that rely on web-based telephony interfaces and real-time communication protocols.
The technical flaw manifests when Asterisk processes specially crafted HTTP requests that attempt to upgrade the connection to a WebSocket protocol. During this upgrade process, the res_http_websocket.so module fails to properly validate the size and structure of incoming WebSocket handshake headers, leading to excessive stack memory consumption. This stack overflow condition occurs because the module allocates stack space based on unvalidated input parameters from the HTTP request, allowing an attacker to supply malformed data that triggers memory exhaustion. The vulnerability operates at the application layer and can be exploited through standard HTTP traffic without requiring authentication or specialized privileges, making it particularly attractive to threat actors seeking to disrupt telephony services.
The operational impact of this vulnerability extends beyond simple service disruption, as it enables denial of service attacks that can completely crash the Asterisk server. When exploited, the stack consumption leads to process termination and system instability, potentially affecting critical communication infrastructure in enterprises, call centers, and telecommunications providers that depend on Asterisk for their voice services. The vulnerability's exploitation requires minimal technical expertise, as attackers only need to send a malformed HTTP request to trigger the memory consumption. This makes the attack surface particularly broad and dangerous for organizations running Asterisk systems in production environments without proper network segmentation or monitoring controls in place.
Organizations affected by this vulnerability should prioritize immediate patching of their Asterisk installations to the latest available versions that contain the necessary security fixes. The remediation process should include thorough testing of patched systems to ensure continued functionality of telephony services and web-based interfaces. Network-level mitigations such as implementing rate limiting on HTTP requests and monitoring for unusual WebSocket upgrade patterns can provide additional defense-in-depth measures. From a security framework perspective, this vulnerability aligns with CWE-129, which addresses improper validation of array index values, and maps to ATT&CK technique T1499.004 for network denial of service attacks. System administrators should also consider implementing intrusion detection systems to monitor for exploitation attempts and establish incident response procedures to address potential service disruptions. The vulnerability underscores the importance of proper input validation in network protocols and highlights the critical need for regular security updates in telephony infrastructure to prevent exploitation of memory corruption vulnerabilities that can lead to complete system compromise.