CVE-2025-62254: Liferay DXP ComboServlet DoS Vulnerability

CVE-2025-62254 Overview

CVE-2025-62254 is a Denial of Service (DoS) vulnerability affecting the ComboServlet component in Liferay Portal and Liferay Digital Experience Platform (DXP). The vulnerability exists because the ComboServlet does not enforce limits on the number or size of files it will combine when processing requests. This allows remote attackers to craft malicious URL query strings that force the server to generate extremely large responses, leading to resource exhaustion and service disruption.

Liferay is a widely-used enterprise portal platform that enables organizations to build and manage digital experiences. The ComboServlet is designed to combine multiple static resources (such as JavaScript and CSS files) into a single response for performance optimization. However, the lack of proper input validation creates an attack surface that can be exploited without authentication.

Critical Impact

Remote attackers can cause denial of service by forcing the ComboServlet to generate excessively large responses, potentially exhausting server memory and bandwidth resources.

Affected Products

• Liferay Portal 7.4.0 through 7.4.3.111 and older unsupported versions
• Liferay DXP 2023.Q4.0 through 2023.Q4.2, 2023.Q3.1 through 2023.Q3.5
• Liferay DXP 7.4 GA through update 92, 7.3 GA through update 35, and older unsupported versions

Discovery Timeline

• 2025-10-23 - CVE-2025-62254 published to NVD
• 2025-11-10 - Last updated in NVD database

Technical Details for CVE-2025-62254

Vulnerability Analysis

The ComboServlet in Liferay Portal is responsible for aggregating multiple static resource files into a single HTTP response. This functionality is intended to reduce the number of HTTP requests required to load a page, improving performance. However, the servlet fails to implement proper validation on the number of files requested or the total size of the combined response.

When processing a request, the servlet reads the file paths from the URL query string and concatenates the contents of each specified file. An attacker can exploit this by crafting requests that specify an excessive number of files or request the same large files multiple times, causing the server to allocate significant memory and CPU resources to build the response.

This type of resource exhaustion attack can degrade the performance of the entire portal, affecting all users, or in severe cases, cause the application server to run out of memory and crash.

Root Cause

The root cause of this vulnerability is improper input validation in the ComboServlet. Specifically, the servlet lacks:

1. Request parameter limits - No maximum limit on the number of files that can be requested in a single combination request
2. Response size limits - No enforcement of a maximum combined response size
3. Rate limiting - No protection against repeated abuse from the same source

The absence of these controls allows attackers to abuse the legitimate file combination functionality to create resource-intensive operations.

Attack Vector

The attack can be executed remotely over the network without any authentication. An attacker crafts a malicious HTTP request to the ComboServlet endpoint, specifying numerous file paths in the URL query string. The server processes each file reference, attempting to read and combine all specified resources into a single response.

The attack is particularly effective because:

• It requires no special privileges or authentication
• The malicious request appears similar to legitimate portal traffic
• A single malicious request can consume significant server resources
• Multiple concurrent requests can quickly overwhelm the server

An attacker might request the combination of the same large resource file hundreds of times, or specify many different valid file paths, forcing the server to allocate memory proportional to the total combined file size.

Detection Methods for CVE-2025-62254

Indicators of Compromise

• Unusual spikes in HTTP requests targeting the ComboServlet endpoint (typically /combo or similar paths)
• Abnormally large HTTP response sizes for static resource requests
• Increased memory consumption on application servers without corresponding user traffic increases
• Server performance degradation or out-of-memory errors in application logs

Detection Strategies

• Monitor HTTP access logs for requests to ComboServlet paths with unusually long query strings or high parameter counts
• Implement alerting on sudden increases in outbound bandwidth consumption from web servers
• Configure application performance monitoring (APM) to detect abnormal servlet response times
• Review server logs for Java heap memory exhaustion warnings or garbage collection pressure

Monitoring Recommendations

• Set up baseline metrics for ComboServlet request patterns and alert on significant deviations
• Monitor server resource utilization (CPU, memory, network) with automated anomaly detection
• Implement request logging that captures query string lengths for forensic analysis
• Configure web application firewall (WAF) rules to log and analyze requests with excessive URL parameters

How to Mitigate CVE-2025-62254

Immediate Actions Required

• Review the Liferay Security Advisory CVE-2025-62254 for official guidance and patches
• Apply the latest security updates from Liferay for your specific product version
• Consider temporarily disabling or restricting access to the ComboServlet if patches cannot be immediately applied
• Implement WAF rules to limit the number of parameters and query string length for affected endpoints

Patch Information

Liferay has acknowledged this vulnerability and provided guidance in their security advisory. Organizations should upgrade to patched versions as specified in the official security advisory. For Liferay Portal, versions beyond 7.4.3.111 should contain the fix. For Liferay DXP, check for the latest quarterly updates beyond 2023.Q4.2 and 2023.Q3.5.

Contact Liferay support for specific patch availability for your product version, especially if running older or unsupported versions.

Workarounds

• Configure web server or reverse proxy to limit URL query string length to reasonable values (e.g., 2048 characters)
• Implement rate limiting on ComboServlet endpoints to prevent abuse from single sources
• Use a WAF to block requests with excessive file combination parameters
• Consider serving static resources through a CDN to reduce load on the application server

# Example nginx configuration to limit query string length
# Add to server or location block for ComboServlet paths
location /combo {
    # Limit URI length including query string
    if ($request_uri ~* "^.{4096,}") {
        return 414 "URI Too Long";
    }
    
    # Rate limiting
    limit_req zone=combo_limit burst=10 nodelay;
    
    proxy_pass http://liferay_backend;
}