1. Introduction
The vulnerability, Apache Struts 2.3.x Showcase App Struts 1 Plugin ActionMessage…, is a potential remote code execution flaw in older versions of the Apache Struts framework. This affects web applications using this Java framework and could allow an attacker to run malicious code on your servers. Systems running vulnerable versions are at risk of complete compromise, impacting confidentiality, integrity, and availability.
2. Technical Explanation
The vulnerability (CVE-2017-9791) stems from improper validation of user input within the ActionMessage class of the Struts 1 plugin showcase app in Apache Struts version 2.3.x. An unauthenticated attacker can exploit this by sending crafted error messages to execute arbitrary code on the server. Nessus has identified this vulnerability based on the application’s self-reported version number, and testing hasn’t been performed.
- Root cause: Insufficient input validation when processing error messages in the ActionMessage class.
- Exploit mechanism: An attacker sends a specially crafted HTTP request containing malicious code within an error message parameter. This triggers remote code execution on the server.
- Scope: Apache Struts 2.3.x running on Windows hosts.
3. Detection and Assessment
Confirming vulnerability requires checking the installed version of Apache Struts. A thorough assessment involves reviewing application logs for suspicious activity related to error message processing.
- Quick checks: Check the web application’s ‘About’ page or configuration files for the Struts version.
- Scanning: Nessus plugin ID 99484 can identify this vulnerability based on reported version information. This is an example only, and further validation may be needed.
- Logs and evidence: Examine web application logs for error messages containing unusual characters or commands. Look for patterns related to the ActionMessage class.
4. Solution / Remediation Steps
The primary solution is to follow the vendor’s recommendations for secure data handling within the ‘ActionMessage’ class. This may involve updating Struts or implementing input validation and sanitization measures.
4.1 Preparation
- A change window may be required depending on your organization’s policies. Approval from the security team might be needed.
4.2 Implementation
- Step 1: Refer to the vendor advisory (https://struts.apache.org/docs/s2-048.html) for specific recommendations on passing data to the ‘ActionMessage’ class.
- Step 3: Restart your web application server to apply the changes.
4.3 Config or Code Example
Before
After
// Secure code example: Input validation before using in ActionMessage class.
String userInput = request.getParameter("userInput");
if (userInput != null && !userInput.isEmpty()) {
// Sanitize the input to remove potentially harmful characters
String sanitizedInput = sanitize(userInput);
ActionMessage message = new ActionMessage(sanitizedInput);
}4.4 Security Practices Relevant to This Vulnerability
Several security practices can help prevent this type of vulnerability. Least privilege reduces the impact if exploited, and input validation blocks unsafe data from reaching vulnerable components. Safe defaults and a regular patch cadence are also important.
- Practice 1: Implement least privilege principles to limit the permissions of the web application user account.
4.5 Automation (Optional)
5. Verification / Validation
Confirming the fix involves checking the Struts version again and verifying that malicious input is no longer executed. A smoke test should ensure core application functionality remains operational.
- Post-fix check: Check the web application’s ‘About’ page or configuration files to confirm the updated Struts version.
- Re-test: Attempt to exploit the vulnerability using a crafted HTTP request with malicious code in an error message parameter. Verify that the code is not executed.
- Smoke test: Test key user actions, such as logging in and accessing core application features, to ensure they still function correctly.
- Monitoring: Monitor web application logs for any unusual activity related to error message processing.
6. Preventive Measures and Monitoring
- Baselines: Update your security baseline to require the latest Apache Struts version or apply specific configuration settings recommended by the vendor.
- Asset and patch process: Implement a regular patch review cycle to ensure that all systems are updated with the latest security fixes in a timely manner.
7. Risks, Side Effects, and Roll Back
- Risk or side effect 2: Potential downtime during server restart. Mitigation: Schedule the update during a maintenance window and communicate any potential service disruptions to users.
- Roll back: Restore the backed-up web application configuration files. Restart the web application server.
8. References and Resources
- Vendor advisory or bulletin: https://struts.apache.org/docs/s2-048.html
- NVD or CVE entry: CVE-2017-9791
- Product or platform documentation relevant to the fix: No further documentation available at this time.