CVE-2018-12541 in Vert.x
Summary
by MITRE
In version from 3.0.0 to 3.5.3 of Eclipse Vert.x, the WebSocket HTTP upgrade implementation buffers the full http request before doing the handshake, holding the entire request body in memory. There should be a reasonnable limit (8192 bytes) above which the WebSocket gets an HTTP response with the 413 status code and the connection gets closed.
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Analysis
by VulDB Data Team • 05/25/2023
The vulnerability identified as CVE-2018-12541 affects Eclipse Vert.x versions 3.0.0 through 3.5.3, specifically within the WebSocket HTTP upgrade implementation. This flaw represents a significant security concern that stems from improper handling of HTTP request buffering during the WebSocket handshake process. The issue manifests when the system accepts and buffers entire HTTP request bodies in memory before initiating the WebSocket handshake, creating an attack surface that can be exploited for resource exhaustion and denial of service conditions.
The technical flaw in this vulnerability resides in the WebSocket upgrade mechanism's design where it fails to implement reasonable buffer size limitations during the HTTP upgrade process. According to CWE-400, this vulnerability maps directly to improper resource management, specifically the lack of input validation and resource limiting in HTTP request processing. The system processes the complete HTTP request body before performing the WebSocket handshake, which means that malicious actors can craft oversized requests that consume excessive memory resources. This behavior violates the principle of least privilege and resource conservation that should be fundamental in secure application design.
The operational impact of this vulnerability extends beyond simple resource consumption issues, creating potential denial of service conditions that can severely impact system availability. When an attacker sends a large HTTP request to a WebSocket endpoint, the server buffers the entire payload in memory before attempting the upgrade, leading to memory exhaustion and potential application crashes. This vulnerability aligns with ATT&CK technique T1499.004, which involves resource exhaustion attacks through excessive requests that consume system resources. The 413 status code response that should be implemented as a mitigation is missing, meaning the system does not properly handle oversized requests and instead continues to buffer them until system resources are depleted.
The mitigation strategy for this vulnerability requires implementing proper request size limiting mechanisms within the WebSocket upgrade process. Organizations should configure reasonable limits on HTTP request body sizes, typically implementing a maximum buffer size of 8192 bytes as recommended in the vulnerability description. This approach aligns with security best practices outlined in the OWASP Top Ten and follows the principle of defense in depth by implementing multiple layers of protection. The fix should involve modifying the WebSocket upgrade implementation to reject requests that exceed predetermined size thresholds before buffering the entire request body, thereby preventing memory exhaustion attacks while maintaining legitimate WebSocket functionality. Additionally, system administrators should monitor and log WebSocket upgrade attempts to detect potential abuse patterns and ensure that the implemented limits are sufficient to handle legitimate traffic while blocking malicious oversized requests.