CVE-2022-26377: Apache HTTP Server Request Smuggling Flaw

CVE-2022-26377 Overview

CVE-2022-26377 is an HTTP Request Smuggling vulnerability in the mod_proxy_ajp module of Apache HTTP Server. This vulnerability arises from inconsistent interpretation of HTTP requests, allowing an attacker to smuggle malicious requests to the backend AJP (Apache JServ Protocol) server that Apache forwards requests to. The vulnerability affects Apache HTTP Server 2.4 version 2.4.53 and all prior versions.

HTTP Request Smuggling vulnerabilities occur when front-end and back-end servers interpret the boundaries of HTTP requests differently. In this case, the mod_proxy_ajp module fails to properly validate and normalize HTTP request boundaries before forwarding them to backend AJP servers, enabling attackers to inject additional unauthorized requests.

Critical Impact

Attackers can exploit this vulnerability to bypass security controls, poison web caches, hijack user sessions, and perform unauthorized actions on backend AJP servers by smuggling malicious requests through the Apache HTTP Server proxy.

Affected Products

• Apache HTTP Server versions 2.4.53 and earlier
• Fedora Project Fedora 35 and 36
• NetApp Clustered Data ONTAP

Discovery Timeline

• 2022-06-09 - CVE-2022-26377 published to NVD
• 2025-05-01 - Last updated in NVD database

Technical Details for CVE-2022-26377

Vulnerability Analysis

This HTTP Request Smuggling vulnerability (CWE-444) exists within the mod_proxy_ajp module of Apache HTTP Server. The root cause lies in how the module processes and interprets HTTP request boundaries when acting as a reverse proxy to AJP backend servers.

The vulnerability enables network-based attacks without requiring authentication or user interaction. When exploited, attackers can achieve high impact on the integrity of the affected system, allowing them to manipulate backend server behavior and potentially bypass authentication or authorization controls.

The AJP protocol is commonly used to connect Apache HTTP Server to application servers like Apache Tomcat. When mod_proxy_ajp incorrectly parses HTTP request headers—particularly Content-Length and Transfer-Encoding headers—it can desynchronize request boundaries between the front-end Apache server and the backend AJP server.

Root Cause

The vulnerability stems from inconsistent interpretation of HTTP request boundaries in the mod_proxy_ajp module. When processing proxied requests, the module fails to properly validate and normalize HTTP request delimiters before forwarding them via AJP protocol to backend servers. This desynchronization between the front-end proxy and back-end server creates an exploitable condition where attackers can inject requests that bypass the proxy's security controls.

Attack Vector

The attack vector is network-based, requiring no authentication or user interaction. An attacker can craft specially formed HTTP requests with ambiguous boundaries that the Apache HTTP Server proxy and the AJP backend server interpret differently.

The exploitation mechanism involves sending HTTP requests with conflicting Content-Length and Transfer-Encoding headers, or other malformed request structures. The front-end Apache server processes the request one way while forwarding data that the backend AJP server interprets as multiple separate requests. This allows the attacker to "smuggle" an unauthorized request that bypasses proxy-level security controls.

Successful exploitation can lead to:

• Bypassing security controls implemented at the proxy level
• Web cache poisoning attacks
• Session hijacking of other users
• Credential theft through request injection
• Unauthorized access to backend application functionality

Detection Methods for CVE-2022-26377

Indicators of Compromise

• Unusual HTTP request patterns with conflicting Content-Length and Transfer-Encoding headers in Apache access logs
• Unexpected backend AJP server behavior or responses that don't correlate with front-end requests
• Log entries showing requests processed by backend servers that were not logged at the proxy level
• Anomalous session activity or authentication bypasses on AJP-connected application servers

Detection Strategies

• Implement deep packet inspection to identify HTTP requests with ambiguous boundary indicators
• Deploy web application firewalls (WAF) configured to detect and block HTTP smuggling patterns
• Enable detailed logging on both Apache HTTP Server and backend AJP servers to correlate request patterns
• Use intrusion detection systems with rules specifically targeting HTTP desynchronization attacks

Monitoring Recommendations

• Monitor Apache error logs for proxy-related warnings and AJP connection anomalies
• Implement real-time alerting for requests containing both Content-Length and Transfer-Encoding headers
• Track request/response count mismatches between proxy and backend servers
• Review access logs for evidence of requests reaching backend servers without corresponding proxy entries

How to Mitigate CVE-2022-26377

Immediate Actions Required

• Upgrade Apache HTTP Server to version 2.4.54 or later, which contains the security fix for this vulnerability
• If immediate patching is not possible, review and restrict access to mod_proxy_ajp configurations
• Implement WAF rules to normalize and validate HTTP request headers before they reach the proxy
• Audit systems using AJP proxy configurations and assess exposure to untrusted networks

Patch Information

Apache has released security patches addressing this vulnerability in Apache HTTP Server version 2.4.54 and later. System administrators should update to the latest stable release as soon as possible. Detailed patching information is available in the Apache HTTP Server Security Vulnerabilities documentation.

Additional vendor-specific patches are available:

• Fedora users should apply updates through the standard package management system
• NetApp customers should review NetApp Security Advisory NTAP-20220624-0005 for Clustered Data ONTAP guidance
• Gentoo users can reference GLSA 202208-20 for update instructions

Workarounds

• Disable mod_proxy_ajp if AJP proxying is not required for your deployment
• Implement strict HTTP request validation at a network perimeter device before traffic reaches Apache
• Configure web application firewalls to reject requests with conflicting Content-Length and Transfer-Encoding headers
• Restrict network access to AJP ports (typically 8009) to only trusted internal hosts

# Disable mod_proxy_ajp if not required
# On Debian/Ubuntu systems:
sudo a2dismod proxy_ajp
sudo systemctl restart apache2

# On RHEL/CentOS systems, comment out the LoadModule directive:
# In /etc/httpd/conf.modules.d/00-proxy.conf
# Comment out: LoadModule proxy_ajp_module modules/mod_proxy_ajp.so
sudo systemctl restart httpd