CVE-2025-65114: Apache Traffic Server DoS Vulnerability

CVE-2025-65114 Overview

Apache Traffic Server allows request smuggling if chunked messages are malformed. This vulnerability affects Apache Traffic Server versions 9.0.0 through 9.2.12 and versions 10.0.0 through 10.1.1. HTTP Request Smuggling vulnerabilities can allow attackers to bypass security controls, poison web caches, and gain unauthorized access to sensitive data by exploiting discrepancies in how front-end and back-end servers parse HTTP requests.

Critical Impact

Attackers can exploit malformed chunked encoding to smuggle malicious requests through Apache Traffic Server, potentially bypassing security controls and accessing protected resources.

Affected Products

• Apache Traffic Server 9.0.0 through 9.2.12
• Apache Traffic Server 10.0.0 through 10.1.1

Discovery Timeline

• 2026-04-02 - CVE CVE-2025-65114 published to NVD
• 2026-04-02 - Last updated in NVD database

Technical Details for CVE-2025-65114

Vulnerability Analysis

This vulnerability is classified under CWE-444 (Inconsistent Interpretation of HTTP Requests), commonly known as HTTP Request Smuggling. The flaw exists in how Apache Traffic Server processes chunked transfer encoding in HTTP requests. When malformed chunked messages are received, the server fails to properly validate and parse the chunk sizes and boundaries, creating a discrepancy between how the proxy interprets the request and how backend servers process it.

The vulnerability allows network-based attacks without requiring authentication or user interaction. An attacker can craft specially malformed chunked HTTP requests that cause Apache Traffic Server to interpret the message boundaries differently than downstream servers, enabling request smuggling attacks that can bypass security controls, hijack user sessions, or poison web caches.

Root Cause

The root cause lies in Apache Traffic Server's inadequate validation of chunked transfer encoding format in HTTP requests. When processing chunked messages, the server does not properly enforce RFC 7230 compliance for chunk size parsing and message termination. This inconsistent handling allows attackers to craft ambiguous requests that are interpreted differently by the proxy and backend servers, creating the conditions necessary for request smuggling.

Attack Vector

The attack is conducted over the network without requiring any privileges or user interaction. An attacker sends specially crafted HTTP requests with malformed chunked encoding to Apache Traffic Server. The malformed chunks exploit parsing differences between the Traffic Server proxy and backend servers. By manipulating chunk boundaries, attackers can prepend malicious content to subsequent requests, effectively "smuggling" unauthorized requests through the proxy layer.

Common exploitation scenarios include:

• Cache poisoning by injecting malicious responses
• Request hijacking to steal credentials or session tokens
• Bypassing security controls such as WAFs and access restrictions
• Credential theft through cross-user request manipulation

Detection Methods for CVE-2025-65114

Indicators of Compromise

• Unusual HTTP requests with malformed or invalid chunked transfer encoding headers
• Log entries showing parsing errors or inconsistencies in chunk size processing
• Unexpected responses being served from cache that don't match legitimate requests
• Backend servers receiving requests that weren't logged by the Traffic Server proxy

Detection Strategies

• Monitor HTTP access logs for requests with malformed Transfer-Encoding: chunked headers
• Implement deep packet inspection rules to detect anomalous chunked encoding patterns
• Deploy web application firewall rules specifically targeting HTTP request smuggling techniques
• Correlate request logs between Apache Traffic Server and backend servers to identify smuggled requests

Monitoring Recommendations

• Enable verbose logging on Apache Traffic Server to capture detailed request parsing information
• Set up alerts for HTTP 400 errors that may indicate malformed request attempts
• Monitor for cache poisoning indicators such as unexpected content being served to users
• Regularly audit proxy-to-backend communication for request/response mismatches

How to Mitigate CVE-2025-65114

Immediate Actions Required

• Upgrade Apache Traffic Server to version 9.2.13 or 10.1.2 immediately
• Review access logs for signs of exploitation attempts before patching
• Implement additional request validation at the web application firewall level
• Consider temporarily disabling chunked transfer encoding if operationally feasible

Patch Information

Apache has released patched versions that address this vulnerability. Users running affected versions should upgrade to:

• Version 9.2.13 for the 9.x branch
• Version 10.1.2 for the 10.x branch

For more information, refer to the Apache Security Discussion Thread.

Workarounds

• Deploy a properly configured reverse proxy or WAF in front of Apache Traffic Server to normalize HTTP requests
• Implement strict HTTP request validation rules that reject malformed chunked encoding
• Consider using HTTP/2 end-to-end where possible, as request smuggling primarily affects HTTP/1.1
• Enforce connection timeouts to limit the window for smuggling attacks

# Configuration example
# Verify Apache Traffic Server version
traffic_server -V

# Example: Restart Traffic Server after upgrade
sudo systemctl restart trafficserver

# Monitor logs for suspicious chunked encoding requests
tail -f /var/log/trafficserver/squid.log | grep -i "chunk"