CVE-2025-23184: Apache CXF DOS Vulnerability

CVE-2025-23184 Overview

A denial of service vulnerability exists in Apache CXF, a popular open-source services framework for building and developing services using frontend programming APIs. The vulnerability stems from improper resource management in the CachedOutputStream class, where instances may not be properly closed in certain edge cases. When these streams are backed by temporary files, this can lead to file system exhaustion, effectively causing a denial of service condition on both servers and clients utilizing the affected framework.

Critical Impact

Attackers can exploit this vulnerability to exhaust file system resources on systems running vulnerable versions of Apache CXF, leading to service disruption and potential system instability affecting both server and client applications.

Affected Products

• Apache CXF versions before 3.5.10
• Apache CXF versions before 3.6.5
• Apache CXF versions before 4.0.6

Discovery Timeline

• 2025-01-21 - CVE-2025-23184 published to NVD
• 2025-12-15 - Last updated in NVD database

Technical Details for CVE-2025-23184

Vulnerability Analysis

This vulnerability is classified as CWE-400 (Uncontrolled Resource Consumption), a category of security weaknesses where an application fails to properly limit the allocation of resources. In Apache CXF, the CachedOutputStream class is designed to buffer output data, optionally spilling to temporary files when the data exceeds a certain threshold. The vulnerability manifests when these cached output streams are not properly closed during specific edge case scenarios.

When the framework processes requests or responses, it may create CachedOutputStream instances to handle large payloads. Under normal operation, these streams should be closed and their associated temporary files deleted. However, in certain edge cases—potentially related to exception handling paths, connection interruptions, or specific data processing conditions—the cleanup routines fail to execute, leaving temporary files on disk.

Root Cause

The root cause lies in improper resource lifecycle management within the CachedOutputStream implementation. The class fails to guarantee cleanup of temporary files in all execution paths, particularly in edge cases where exceptions occur or processing is interrupted before the normal cleanup routines can execute. This represents a classic resource leak pattern where resources acquired during operation are not reliably released.

The issue affects both client and server components of Apache CXF, as both utilize the CachedOutputStream class for handling message bodies that exceed memory thresholds. Without proper finally blocks or try-with-resources patterns ensuring cleanup, temporary files accumulate over time.

Attack Vector

This vulnerability is exploitable over the network without requiring authentication or user interaction. An attacker can exploit this vulnerability by sending specially crafted requests to a vulnerable Apache CXF service that trigger the edge case conditions where CachedOutputStream instances are not properly closed.

The attack scenario involves repeatedly sending requests that cause the framework to create temporary files that are never cleaned up. Over time, this leads to:

1. Disk space exhaustion on the target system
2. Potential inode exhaustion on file systems with limited inodes
3. Service degradation as disk I/O becomes constrained
4. Complete service unavailability when the file system becomes full

The exploitation does not require complex attack techniques—an attacker simply needs to identify request patterns that trigger the vulnerable code paths and automate the sending of such requests. Since the vulnerability affects both servers and clients, a malicious server could also exploit vulnerable CXF clients by sending responses that trigger the same file accumulation behavior.

Detection Methods for CVE-2025-23184

Indicators of Compromise

• Unusual accumulation of temporary files in the system's temporary directory (typically /tmp on Linux or %TEMP% on Windows)
• Temporary files with patterns consistent with Apache CXF output caching (often prefixed with cxf or related identifiers)
• Gradual decrease in available disk space without corresponding application data growth
• File system warnings or errors related to disk space or inode exhaustion

Detection Strategies

• Monitor disk space utilization on systems running Apache CXF applications with alerting thresholds
• Implement file count monitoring for temporary directories to detect abnormal file accumulation
• Review Apache CXF application logs for stream-related warnings or exceptions
• Use application performance monitoring (APM) tools to track resource usage patterns in CXF services

Monitoring Recommendations

• Configure disk space alerts at 80% and 90% utilization thresholds for early warning
• Implement automated cleanup scripts for orphaned temporary files older than expected processing times
• Monitor the count and age of temporary files created by CXF applications
• Enable verbose logging during investigation to identify the specific edge cases triggering the leak

How to Mitigate CVE-2025-23184

Immediate Actions Required

• Upgrade Apache CXF to version 3.5.10, 3.6.5, or 4.0.6 or later depending on your current major version branch
• Review and increase available disk space on affected systems as a temporary measure
• Implement monitoring for temporary file accumulation to detect active exploitation attempts
• Configure automated cleanup of temporary files as an interim mitigation

Patch Information

Apache has released patched versions that address the improper resource handling in CachedOutputStream. Organizations should upgrade to the following versions based on their current deployment:

• For 3.5.x branch: Upgrade to version 3.5.10 or later
• For 3.6.x branch: Upgrade to version 3.6.5 or later
• For 4.0.x branch: Upgrade to version 4.0.6 or later

Additional technical details are available through the Apache Mailing List Thread and the OpenWall OSS-Security Post. Organizations using NetApp products should also review the NetApp Security Advisory.

Workarounds

• Implement a scheduled task to clean up orphaned temporary files from the CXF temporary directory
• Increase the memory threshold for CachedOutputStream to reduce the likelihood of temporary file creation (at the cost of increased memory usage)
• Configure separate temporary directories for CXF with appropriate disk quotas to contain the impact
• Implement rate limiting on incoming requests to reduce the potential speed of file system exhaustion

# Example: Temporary file cleanup cron job (Linux)
# Clean CXF temporary files older than 1 hour
0 * * * * find /tmp -name 'cxf*' -type f -mmin +60 -delete 2>/dev/null

# Monitor temporary file count
*/5 * * * * echo "$(date): $(find /tmp -name 'cxf*' -type f | wc -l) CXF temp files" >> /var/log/cxf-temp-monitor.log