CVE-2020-27223 in REST Data Services
Summary
by MITRE • 02/27/2021
In Eclipse Jetty 9.4.6.v20170531 to 9.4.36.v20210114 (inclusive), 10.0.0, and 11.0.0 when Jetty handles a request containing multiple Accept headers with a large number of “quality” (i.e. q) parameters, the server may enter a denial of service (DoS) state due to high CPU usage processing those quality values, resulting in minutes of CPU time exhausted processing those quality values.
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Analysis
by VulDB Data Team • 08/20/2025
The vulnerability identified as CVE-2020-27223 affects the Eclipse Jetty web server software within specific version ranges including 9.4.6.v20170531 through 9.4.36.v20210114, as well as versions 10.0.0 and 11.0.0. This issue represents a denial of service condition that can severely impact server availability and performance. The flaw manifests when the web server processes HTTP requests containing multiple Accept headers with an excessive number of quality parameters, creating a scenario where computational resources become consumed disproportionately. The vulnerability operates at the application layer of the network stack and directly impacts the server's ability to handle concurrent requests effectively.
The technical root cause of this vulnerability lies in the inefficient parsing and processing of quality values within HTTP Accept headers. When multiple Accept headers are present in a request, the Jetty server must parse each quality parameter to determine content negotiation preferences. The vulnerability exploits a weakness in the parsing algorithm that becomes increasingly computationally expensive as the number of quality parameters grows. This processing overhead can cause the server to consume excessive CPU cycles, potentially leading to complete service unavailability for legitimate users. The issue is particularly dangerous because it can be triggered through simple HTTP requests without requiring authentication or special privileges, making it an attractive target for attackers seeking to disrupt services. This behavior aligns with CWE-400, which categorizes the vulnerability as an uncontrolled resource consumption issue, and reflects patterns commonly associated with denial of service attacks in web applications.
The operational impact of CVE-2020-27223 extends beyond simple service disruption to potentially cause cascading failures within larger system architectures. When a Jetty server enters the high CPU usage state, it becomes unable to process legitimate requests effectively, leading to request timeouts and connection failures for legitimate users. The duration of the DoS condition can be significant, with the vulnerability requiring minutes of CPU time to process the malformed requests, which can severely impact user experience and business operations. Organizations relying on Jetty-based applications may experience degraded service quality, increased latency, and potential revenue loss during attack periods. The vulnerability's impact is particularly severe in high-traffic environments where the server is already operating near capacity, as the additional CPU load can push systems over their processing limits and cause complete service outages. This vulnerability can be exploited through the ATT&CK technique of resource exhaustion, specifically targeting the availability aspect of the CIA triad.
Mitigation strategies for CVE-2020-27223 primarily involve upgrading to patched versions of the Eclipse Jetty software, specifically versions that address the quality parameter parsing inefficiency. Organizations should implement immediate patch management procedures to upgrade their Jetty installations to versions that contain the necessary security fixes. Additionally, implementing request rate limiting and header validation mechanisms can provide defense-in-depth protection against this vulnerability. Network-level controls such as web application firewalls can be configured to detect and block requests containing excessive quality parameters in Accept headers. Organizations should also consider implementing monitoring solutions that can detect unusual CPU usage patterns and alert administrators to potential DoS conditions. Input validation controls should be strengthened to limit the number of Accept headers and quality parameters that can be processed in a single request, preventing the exploitation of this vulnerability through malformed HTTP requests.