CVE-2025-1948 in Jetty
Summary
by MITRE • 05/08/2025
In Eclipse Jetty versions 12.0.0 to 12.0.16 included, an HTTP/2 client can specify a very large value for the HTTP/2 settings parameter SETTINGS_MAX_HEADER_LIST_SIZE. The Jetty HTTP/2 server does not perform validation on this setting, and tries to allocate a ByteBuffer of the specified capacity to encode HTTP responses, likely resulting in OutOfMemoryError being thrown, or even the JVM process exiting.
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Analysis
by VulDB Data Team • 08/10/2025
The vulnerability described in CVE-2025-1948 represents a critical memory exhaustion flaw within the Eclipse Jetty HTTP/2 implementation that affects versions 12.0.0 through 12.0.16. This issue stems from the server's failure to validate the SETTINGS_MAX_HEADER_LIST_SIZE parameter provided by HTTP/2 clients during the connection establishment phase. The HTTP/2 protocol allows clients to communicate various settings to servers through the SETTINGS frame, with SETTINGS_MAX_HEADER_LIST_SIZE specifically controlling the maximum size of header lists that the client will accept. When an attacker crafts a malicious HTTP/2 client that specifies an extraordinarily large value for this parameter, the Jetty server processes this without proper validation, leading to catastrophic memory allocation attempts.
The technical execution of this vulnerability occurs during the HTTP/2 connection setup where the server receives the SETTINGS frame from a client and attempts to allocate memory resources based on the client-specified capacity. This flaw directly maps to CWE-129, which addresses insufficient validation of length parameters, and CWE-770, concerning allocation of resources without proper limits. The server's failure to implement bounds checking on the SETTINGS_MAX_HEADER_LIST_SIZE parameter creates an attack surface where malicious actors can trigger excessive memory consumption. When the server attempts to allocate a ByteBuffer of the specified enormous capacity, it inevitably leads to OutOfMemoryError exceptions that can cause the entire JVM process to terminate, resulting in a denial of service condition that affects all legitimate users of the service.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the entire application infrastructure. An attacker can exploit this weakness by establishing an HTTP/2 connection with a malicious client that specifies a massive value for SETTINGS_MAX_HEADER_LIST_SIZE, causing the server to attempt allocation of gigabytes or even terabytes of memory. This memory exhaustion can occur repeatedly, allowing for sustained denial of service attacks that may be difficult to distinguish from legitimate high-volume traffic patterns. The vulnerability affects any system running affected Jetty versions that accept HTTP/2 connections, making it particularly dangerous for web applications, microservices, and API gateways that rely on HTTP/2 for performance optimization. The attack vector is particularly insidious because it requires minimal sophistication to execute, as the attacker only needs to configure an HTTP/2 client with a large parameter value rather than complex exploit development.
Mitigation strategies for CVE-2025-1948 should prioritize immediate version upgrades to Jetty 12.0.17 or later, which contain the necessary validation patches for the SETTINGS_MAX_HEADER_LIST_SIZE parameter. Organizations should also implement network-level controls to monitor and restrict HTTP/2 traffic patterns, particularly focusing on unusual SETTINGS parameter values that exceed reasonable thresholds. The implementation of resource limits and memory constraints at the JVM level can provide additional protection layers, though these measures are secondary to the core patching approach. Security teams should monitor for potential exploitation attempts by analyzing connection patterns and memory usage metrics for unusual spikes that might indicate this attack in progress. Additionally, the vulnerability demonstrates the importance of implementing proper input validation and resource boundary checking for all protocol parameters, aligning with ATT&CK technique T1499.004 for resource exhaustion attacks and emphasizing the need for robust defensive programming practices that prevent unbounded resource allocation. Organizations should also consider implementing rate limiting and connection pooling controls that can help detect and prevent abnormal HTTP/2 client behavior before it can cause memory exhaustion.