Apache HTTP Server AJP Smuggling (CVE-2022-26377): Anatomy of a High-Impact Proxy Flaw

Introduction

A single malformed HTTP header can open the door to backend compromise, bypassing authentication and security controls with a single request. CVE-2022-26377, a high-severity flaw in Apache HTTP Server's mod_proxy_ajp module, has proven just how dangerous protocol desynchronization can be in modern web infrastructure. Attackers have leveraged this bug to smuggle unauthorized requests into backend AJP servers, impacting not only Apache deployments but also major enterprise products like NetApp ONTAP and IBM QRadar.

About the Parties Involved:

Apache Software Foundation: Maintains the Apache HTTP Server, the world's most widely deployed web server, powering a significant portion of the internet.
NetApp: A global leader in data management and storage, with solutions deployed in large enterprises and cloud environments.
IBM: One of the largest technology companies, with its HTTP Server and QRadar SIEM products used in critical infrastructure worldwide.

Technical Information

Vulnerability Mechanism

CVE-2022-26377 is rooted in the inconsistent parsing of HTTP request headers between Apache HTTP Server's mod_proxy_ajp module and the backend AJP (Apache JServ Protocol) server. The flaw specifically affects Apache HTTP Server versions 2.4.0 through 2.4.53 when mod_proxy_ajp is enabled and configured to forward requests to an AJP backend (e.g., Tomcat).

Exploitation Details

Trigger: The attacker sends an HTTP request with a malformed or duplicated Transfer-Encoding: chunked, chunked header.
Apache Behavior: Apache strips the Content-Length header but does not properly validate the non-standard Transfer-Encoding value.
Result: The body of the HTTP request can contain additional, attacker-controlled AJP packets.
Backend Behavior: The backend AJP server (such as Tomcat) may interpret these as separate requests, enabling HTTP request smuggling.

This discrepancy allows an attacker to inject hidden requests that bypass frontend security controls, potentially leading to:

Unauthorized access to backend applications
Session hijacking via cookie injection
Cache poisoning
Cross-site scripting (XSS) propagation

Example Attack Flow

POST /target HTTP/1.1
Host: vulnerable-server
Transfer-Encoding: chunked, chunked
Content-Length: 524

[malicious AJP packet here]

The backend AJP server may process the malicious AJP packet as a separate, valid request, enabling the attacker to interact with internal resources or escalate privileges.

Affected Configurations

Apache HTTP Server with mod_proxy_ajp enabled
Backend AJP servers (e.g., Tomcat, IBM WebSphere)
Common in enterprise deployments and products that rely on Apache as a frontend proxy

Attack Vectors

Direct exploitation by sending crafted HTTP requests to vulnerable Apache servers
Chained attacks leveraging public proof-of-concept code to target downstream products (e.g., IBM QRadar, NetApp ONTAP)
Automated exploitation via offensive security frameworks

Patch Information

In the latest release of Apache HTTP Server, version 2.4.64, several critical vulnerabilities have been addressed to enhance the server's security and stability.

HTTP Response Splitting (CVE-2024-42516): Proper validation and sanitization of response headers
SSRF with mod_headers (CVE-2024-43204): Stricter validation of header modifications
SSRF on Windows Due to UNC Paths (CVE-2024-43394): Restricts server's ability to process UNC paths from untrusted sources
mod_ssl Error Log Variable Escaping (CVE-2024-47252): Ensures all log variables are properly escaped
mod_ssl Access Control Bypass (CVE-2025-23048): Enforces stricter session validation
mod_proxy_http2 Denial of Service (CVE-2025-49630): Improves input validation
mod_ssl TLS Upgrade Attack (CVE-2025-49812): Removes support for TLS upgrades in certain contexts
HTTP/2 DoS by Memory Increase (CVE-2025-53020): Ensures timely release of memory resources

Upgrade Guidance:

Upgrade to Apache HTTP Server 2.4.64 to remediate CVE-2022-26377 and related vulnerabilities.

Patch Source: Apache HTTP Server Security Vulnerabilities

Detection Methods

Detecting HTTP request smuggling vulnerabilities, such as CVE-2022-26377, requires a multifaceted approach due to the subtle nature of these attacks. The core of this vulnerability lies in the inconsistent interpretation of HTTP request headers between the Apache HTTP Server's mod_proxy_ajp module and the AJP server it forwards requests to. This discrepancy can be exploited to smuggle malicious requests, potentially leading to unauthorized actions or data manipulation.

Indicators of Compromise (IoCs):

Anomalous Log Entries: Look for HTTP requests in server logs that contain multiple or conflicting Content-Length and Transfer-Encoding headers. Such discrepancies can indicate attempts to exploit request smuggling vulnerabilities.
Unexpected 4xx or 5xx Responses: A surge in client errors (4xx) or server errors (5xx) without corresponding legitimate requests may suggest that smuggled requests are causing unintended behavior.
Unusual Backend Behavior: Monitor for unexpected actions on backend systems that do not correlate with logged frontend requests, as this may indicate that smuggled requests are being processed.

Detection Strategies:

Log Analysis: Regularly review server logs for irregularities in HTTP headers, especially focusing on duplicate or conflicting Content-Length and Transfer-Encoding headers. Automated log analysis tools can assist in identifying these patterns.
Traffic Inspection: Deploy network monitoring tools capable of deep packet inspection to analyze HTTP traffic for anomalies indicative of request smuggling attempts.
Security Testing: Utilize security scanners and penetration testing tools that specifically test for HTTP request smuggling vulnerabilities. These tools can simulate attack scenarios to identify potential weaknesses.
Web Application Firewalls (WAFs): Configure WAFs to detect and block malformed HTTP requests that could be used in smuggling attacks. Ensure that the WAF rules are up-to-date and tailored to recognize patterns associated with request smuggling.

Monitoring Guidance:

Regular Updates: Keep all components of the web server and proxy configurations updated to the latest versions, as patches for known vulnerabilities are often included in updates.
Configuration Reviews: Periodically review and audit server and proxy configurations to ensure that they adhere to security best practices and do not inadvertently allow for inconsistent request parsing.
Incident Response Planning: Develop and maintain an incident response plan that includes procedures for detecting, analyzing, and mitigating HTTP request smuggling attacks.

Detection Source: GitHub PoC and Analysis

Affected Systems and Versions

Apache HTTP Server: Versions 2.4.0 through 2.4.53 with mod_proxy_ajp enabled
NetApp Clustered Data ONTAP: Affected via bundled Apache HTTP Server
IBM HTTP Server and QRadar: Affected via inherited Apache codebase
Fedora Linux: Fedora 35/36 with vulnerable Apache packages
Other downstream products: Any software or appliance using Apache HTTP Server with mod_proxy_ajp in the vulnerable version range

Vendor Security History

Apache: Generally strong security response, with a mature disclosure process and relatively prompt patch cycles for high-severity issues. Fix for CVE-2022-26377 released in version 2.4.54 within a few months of discovery. Previous issues with HTTP parsing and request smuggling have been reported and patched in the past, highlighting the complexity of proxy protocol handling.
NetApp and IBM: Both vendors issued advisories and patches in response to the disclosure, with NetApp releasing NTAP-20220624-0005 and IBM updating QRadar and HTTP Server products.

References

Source: This report was created using AI

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