CVE-2019-10072 in Siebel Apps - Marketing
Summary
by MITRE
The fix for CVE-2019-0199 was incomplete and did not address HTTP/2 connection window exhaustion on write in Apache Tomcat versions 9.0.0.M1 to 9.0.19 and 8.5.0 to 8.5.40 . By not sending WINDOW_UPDATE messages for the connection window (stream 0) clients were able to cause server-side threads to block eventually leading to thread exhaustion and a DoS.
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Analysis
by VulDB Data Team • 11/25/2020
The vulnerability described in CVE-2019-10072 represents a critical security flaw in Apache Tomcat web server implementations that specifically affects HTTP/2 protocol handling. This issue stems from an incomplete remediation of a previously identified vulnerability CVE-2019-0199, which highlights the complexity of addressing protocol-level security concerns in web infrastructure components. The flaw manifests in versions ranging from 9.0.0.M1 through 9.0.19 and 8.5.0 through 8.5.40, indicating a widespread impact across multiple major release branches of the Tomcat server software.
The technical root cause of this vulnerability lies in the improper handling of HTTP/2 connection window management during write operations. In HTTP/2 protocol specifications, connection windows are essential mechanisms that control the flow of data between client and server, preventing one side from overwhelming the other with data. The flaw occurs specifically on stream 0, which represents the connection-level stream in HTTP/2, where the server fails to properly send WINDOW_UPDATE messages. These messages are critical for informing the remote peer about available buffer space and allowing continued data transmission. When these updates are not sent, the connection window becomes exhausted, creating a condition where the server cannot properly manage data flow.
The operational impact of this vulnerability is severe and manifests as a denial-of-service condition that can effectively cripple web server functionality. Attackers can exploit this flaw by sending carefully crafted HTTP/2 requests that consume the connection window buffer space without triggering proper window updates. As the server's threads become blocked waiting for available window space, they eventually exhaust the thread pool available to handle incoming requests. This thread exhaustion creates a cascading failure where legitimate users cannot establish new connections or process existing requests, effectively rendering the web application unavailable to authorized users. The vulnerability specifically targets server-side thread resources, making it particularly dangerous in high-traffic environments where thread management is critical for performance.
From a cybersecurity perspective, this vulnerability aligns with CWE-400, which addresses unchecked resource consumption, and represents a classic example of a resource exhaustion attack pattern. The flaw also relates to ATT&CK technique T1499.004, which covers network denial of service attacks, demonstrating how protocol-level implementation errors can be weaponized for service disruption. The incomplete fix for CVE-2019-0199 suggests that the remediation process failed to fully address all aspects of the connection window management, leaving a persistent weakness that attackers can exploit. Organizations running affected Tomcat versions face significant risk of service disruption, particularly in environments where HTTP/2 is enabled and actively used, as the vulnerability can be exploited with relatively simple HTTP/2 client implementations.
The mitigation strategy for this vulnerability requires immediate patching of affected Tomcat versions to the corrected releases that properly implement HTTP/2 window management. Organizations should also consider implementing connection rate limiting and monitoring for unusual patterns in HTTP/2 traffic that might indicate exploitation attempts. Additionally, administrators should review their server configurations to ensure that HTTP/2 is properly enabled with appropriate buffer management settings, and consider temporarily disabling HTTP/2 if the vulnerability cannot be immediately patched. The vulnerability serves as a reminder of the critical importance of thorough testing and validation of security patches, particularly for protocol-level implementations where subtle errors can have significant operational consequences.