CVE-2018-7287 in Asterisk
Summary
by MITRE
An issue was discovered in res_http_websocket.c in Asterisk 15.x through 15.2.1. If the HTTP server is enabled (default is disabled), WebSocket payloads of size 0 are mishandled (with a busy loop).
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Analysis
by VulDB Data Team • 02/04/2021
The vulnerability identified as CVE-2018-7287 represents a critical denial of service flaw within the Asterisk telephony platform affecting versions 15.x through 15.2.1. This issue resides in the res_http_websocket.c module which handles websocket connections through the HTTP server component. The vulnerability manifests when the HTTP server is enabled, which is the default configuration in many deployments, creating a significant risk for organizations relying on Asterisk for their communication infrastructure. The flaw specifically targets the handling of zero-sized WebSocket payloads, which can be exploited by malicious actors to disrupt service availability.
The technical implementation of this vulnerability stems from improper input validation within the websocket processing logic. When a WebSocket frame with a payload size of zero is received, the Asterisk application enters an infinite loop or busy loop condition where it continuously processes the malformed data without proper termination conditions. This busy loop consumes excessive CPU resources and prevents the system from processing legitimate requests, effectively creating a denial of service condition. The flaw demonstrates poor error handling practices and inadequate bounds checking for websocket frame processing, particularly when dealing with edge cases such as empty payloads. This type of vulnerability falls under CWE-835, which specifically addresses the issue of infinite loops or busy loops in software implementations, and represents a classic example of resource exhaustion through improper input handling.
The operational impact of CVE-2018-7287 extends beyond simple service disruption to potentially compromise entire communication infrastructures. Organizations running Asterisk systems with HTTP server enabled are at risk of experiencing complete service outages, particularly in environments where telephony services are mission-critical. The vulnerability can be exploited remotely without authentication, making it particularly dangerous in networked environments where attackers can easily access the HTTP endpoints. This flaw directly maps to ATT&CK technique T1499.004, which covers network denial of service attacks, and represents a significant threat to business continuity and communication reliability. The impact is amplified because many organizations have Asterisk systems deployed in production environments where the HTTP server is enabled for various management and integration purposes, inadvertently exposing themselves to this vulnerability.
Mitigation strategies for CVE-2018-7287 should focus on immediate patching of affected Asterisk versions to 15.2.2 or later, which contains the necessary fixes for proper websocket payload handling. Organizations should also consider disabling the HTTP server component entirely if it is not required for their specific use cases, as this eliminates the attack surface entirely. Network segmentation and access controls can provide additional protection by limiting exposure to the vulnerable HTTP endpoints. Security monitoring should include detection of unusual CPU usage patterns and websocket connection behavior that might indicate exploitation attempts. System administrators should implement proper input validation and resource limiting measures to prevent similar vulnerabilities from manifesting in other components. The fix implemented by the Asterisk development team addresses the core issue through improved bounds checking and proper termination conditions for websocket frame processing, aligning with security best practices for preventing resource exhaustion attacks and ensuring robust error handling in network services.