Overview
This report delves into the details of a significant vulnerability identified in Apache Tomcat, an open-source Java Servlet container developed by the Apache Software Foundation. The vulnerability, designated as CVE-2025-53506, represents a serious risk to servers running the affected versions of Apache Tomcat. If exploited, this flaw could lead to uncontrolled resource consumption, potentially leading to system compromise or data leakage.
Vulnerability Summary
CVE ID: CVE-2025-53506
Severity: High (7.5 CVSS score)
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: Potential system compromise or data leakage
Affected Products
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Product | Affected Versions
Apache Tomcat | 11.0.0-M1 through 11.0.8
Apache Tomcat | 10.1.0-M1 through 10.1.42
Apache Tomcat | 9.0.0.M1 through 9.0.106
How the Exploit Works
The vulnerability exploits a flaw in Apache Tomcat’s handling of HTTP/2 clients. If an HTTP/2 client does not acknowledge the initial settings frame that reduces the maximum permitted concurrent streams, it can lead to uncontrolled resource consumption. This can cause the server to become overwhelmed and potentially lead to system compromise or data leakage.
Conceptual Example Code
Here’s a concept of how this vulnerability might be exploited:
POST / HTTP/2.0
Host: vulnerable.example.com
:method: POST
:path: /
:scheme: https
:authority: vulnerable.example.com
content-length: 1000000000
{ "malicious_payload": "Repeatedly send large amounts of data without acknowledging initial settings frame." }
This conceptual exploit demonstrates the malicious client repeatedly sending large amounts of data without acknowledging the initial settings frame, leading to uncontrolled resource consumption on the server.

