CVE-2017-2670 in Undertow
Summary
by MITRE
It was found in Undertow before 1.3.28 that with non-clean TCP close, the Websocket server gets into infinite loop on every IO thread, effectively causing DoS.
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Analysis
by VulDB Data Team • 04/27/2023
The vulnerability identified as CVE-2017-2670 affects the Undertow web server component, specifically manifesting in versions prior to 1.3.28. This issue represents a critical denial of service vulnerability that stems from improper handling of TCP connection termination sequences. The flaw occurs when Undertow encounters websocket connections that are closed without proper cleanup procedures, creating a scenario where the server's IO threads become trapped in an infinite loop. This behavior fundamentally undermines the server's ability to process subsequent requests and maintain operational continuity.
The technical root cause of this vulnerability lies in Undertow's websocket server implementation which fails to properly manage the cleanup process when TCP connections are terminated abruptly without following standard closure protocols. When a websocket connection experiences what is termed a "non-clean TCP close," the server's internal state management becomes inconsistent, leading to an infinite loop within the IO thread execution context. This condition specifically impacts the server's event handling mechanisms, where the websocket server continuously processes the same malformed connection state without proper termination or recovery procedures. The vulnerability operates at the protocol handling level, where the server's websocket implementation lacks adequate error recovery mechanisms for abnormal connection termination scenarios.
The operational impact of CVE-2017-2670 is severe and directly translates to service disruption for affected systems. When exploited, this vulnerability causes a complete denial of service condition where the affected Undertow server becomes unresponsive to new connections or requests. The infinite loop consumes CPU resources continuously on the IO threads, effectively rendering the server incapable of processing legitimate user requests. This condition can be triggered by a single malicious client or through automated tools that establish websocket connections and then abruptly terminate them without proper closure sequences. The impact extends beyond immediate service unavailability to potentially affecting system stability and resource allocation across the entire hosting environment.
Organizations affected by this vulnerability should immediately implement mitigations including upgrading to Undertow version 1.3.28 or later, which contains the necessary patches to address the websocket connection cleanup issue. Network-level mitigations such as implementing connection rate limiting and monitoring for abnormal websocket termination patterns can provide additional protection. Security teams should also consider implementing intrusion detection systems that can identify and alert on websocket connection anomalies that may indicate exploitation attempts. The vulnerability aligns with CWE-835, which addresses infinite loops in software implementations, and maps to ATT&CK technique T1499.004 for resource exhaustion attacks. Organizations should also review their websocket implementations and ensure proper connection lifecycle management to prevent similar issues in other components of their infrastructure.