CVE-2025-53506: Apache Tomcat HTTP/2 DoS Vulnerability

CVE-2025-53506 Overview

The CVE-2025-53506 vulnerability involves uncontrolled resource consumption in Apache Tomcat when an HTTP/2 client does not acknowledge the initial settings frame that reduces the maximum permitted concurrent streams. This issue impacts Apache Tomcat versions from 11.0.0-M1 through 11.0.8, 10.1.0-M1 through 10.1.42, and 9.0.0.M1 through 9.0.106, as well as certain EOL versions.

Critical Impact
This vulnerability can lead to Denial of Service (DoS) by exhausting server resources, affecting availability.

Affected Products

Apache Tomcat 11.0.0-M1 to 11.0.8
Apache Tomcat 10.1.0-M1 to 10.1.42
Apache Tomcat 9.0.0.M1 to 9.0.106

Discovery Timeline

Not Available - Vulnerability discovered by Not Available
Not Available - Responsible disclosure to Apache
Not Available - CVE CVE-2025-53506 assigned
Not Available - Apache releases security patch
2025-07-10 - CVE CVE-2025-53506 published to NVD
2025-11-04 - Last updated in NVD database

Technical Details for CVE-2025-53506

Vulnerability Analysis

The vulnerability stems from Apache Tomcat's HTTP/2 implementation where problematic client behavior can lead to server resource exhaustion. If a client does not acknowledge the HTTP/2 settings frame, the server resources may be consumed unnecessarily, leading to a potential Denial of Service (DoS) situation.

Root Cause

The root cause lies in the inadequate handling of HTTP/2 stream management where the failure to acknowledge settings leads to unchecked resource allocation.

Attack Vector

This vulnerability can be exploited remotely over the network by a malicious HTTP/2 client.

bash

// Example exploitation code (sanitized)
# Malicious HTTP/2 request simulation
curl -X GET http://vulnerable-server.com:8080/path --http2

Detection Methods for CVE-2025-53506

Indicators of Compromise

Unexpected spikes in server resource utilization
Log entries showing HTTP/2 connection anomalies
Abnormal HTTP/2 settings frame logs

Detection Strategies

Implement network monitoring tools to detect spikes in connection attempts or resource usage. Analyze HTTP/2 traffic patterns for anomalies such as unacknowledged settings frames.

Monitoring Recommendations

Deploy SentinelOne's Behavioral Detection capabilities to continuously monitor server behavior for signs of resource exhaustion and alert on unusual HTTP/2 connection patterns.

How to Mitigate CVE-2025-53506

Immediate Actions Required

Update Apache Tomcat to the latest secure versions (11.0.9, 10.1.43, 9.0.107)
Apply rate limiting on HTTP/2 connections
Monitor and reset excessive connections

Patch Information

Patches for affected versions are available in Apache Tomcat versions 11.0.9, 10.1.43, and 9.0.107, which address these deficiencies.

Workarounds

Increase monitoring and set alerts for HTTP/2 traffic anomalies. Deploy SentinelOne's comprehensive endpoint protection to mitigate resource-intensive attacks.