Apache Struts 2 Struts 1 Plugin Remote Code Execution Vulnerability (CVE-2017-9791, S2-048) Analysis and Mitigation Guide
Executive & SecOps Summary
SECOPS ASSESSMENTWeb applications running Apache Struts 2.1.x and 2.3.x that utilize the Struts 1 integration plugin (struts2-struts1-plugin)
Unauthenticated remote attackers can execute arbitrary system commands under the privileges of the web server, leading to complete system compromise
Upgrade to the latest supported Apache Struts 2.5.x+ versions, or completely disable and remove the struts2-struts1-plugin dependency
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
The most effective remediation is to remove the obsolete Struts 1 plugin dependency or upgrade to a secure, supported version of Apache Struts. For Maven-based projects, remove or update the dependency in your pom.xml:
<!-- Example: Remove the vulnerable Struts 1 plugin dependency from pom.xml -->
<dependency>
<groupId>org.apache.struts</groupId>
<artifactId>struts2-struts1-plugin</artifactId>
<!-- It is highly recommended to completely remove this dependency -->
</dependency>2. Temporary Workaround & Hardening Configuration
If immediate patching is not feasible, deploy Web Application Firewall (WAF) rules to block common OGNL injection patterns. Additionally, refactor application code to avoid passing raw user input directly into ActionMessage constructors.
<!-- Code-level mitigation example -->
<!-- Avoid: messages.add('key', new ActionMessage(userInput)); -->
<!-- Secure: Use defined resource bundle keys instead of raw user input -->
<!-- messages.add('key', new ActionMessage('errors.required', userInput)); -->3. Log Audit & IoC Verification Commands
Use the following Bash script to scan web server access logs for potential OGNL injection payloads targeting S2-048.
#!/bin/bash
# Scan web server logs for S2-048 (CVE-2017-9791) exploitation attempts
LOG_PATH='/var/log/apache2'
echo '[*] Searching for OGNL injection patterns in logs...'
egrep -i '(#context|ognl|java\.lang\.Runtime|ProcessBuilder)' ${LOG_PATH}/*.log
if [ $? -eq 0 ]; then
echo '[WARNING] Suspicious OGNL payloads detected in access logs!'
else
echo '[INFO] No obvious S2-048 exploitation attempts found.'
fiBlock Exploits Instantly with Managed Virtual Patching Rules
Can't patch production immediately? Deploy managed WAF rules at the edge to intercept RCE, SQLi, and deserialization payloads before they hit your origin server.
Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2017-9791, also known as S2-048) is an input validation bypass (CWE-20) in the Apache Struts 2 integration plugin for Struts 1 (struts2-struts1-plugin). When wrapping Struts 1 Actions within Struts 2, untrusted user inputs passed in raw messages to ActionMessage are processed without sufficient sanitization. This allows the input to be interpreted and evaluated as OGNL (Object-Graph Navigation Language) expressions by the Struts 2 framework.
2. Exploitation Mechanics & Attack Scenario
An attacker crafts a malicious HTTP request containing OGNL syntax (e.g., ${#context...} or %{...}) within form fields or request parameters. When the vulnerable plugin binds these inputs to an ActionMessage and processes them via message resolution methods like getText(), the OGNL engine parses and executes the payload. By leveraging Java reflection and classes such as java.lang.Runtime or java.lang.ProcessBuilder within the OGNL expression, the attacker can execute arbitrary OS commands on the hosting server.
3. Infrastructure & Business Impact
With a CVSS score of 9.8 (Critical) and inclusion in the CISA KEV catalog, this vulnerability represents a severe threat vector that has been actively exploited in the wild. Successful exploitation grants attackers shell access to the application server, enabling lateral movement, database exfiltration, deployment of ransomware, and complete compromise of the enterprise infrastructure.
Official Vendor Advisories & References
The Struts 1 plugin in Apache Struts 2.1.x and 2.3.x might allow remote code execution via a malicious field value passed in a raw message to the ActionMessage.
Frequently Asked SecOps Questions (CVE-2017-9791)
FAQQ1. How critical is CVE-2017-9791 and is it actively exploited in the wild?
CVE-2017-9791 is rated CVSS 9.8 (CRITICAL) with a 30-day EPSS exploitation probability of 98.9%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2017-9791?
Primary impacted vendors include apache across struts. Scope summary: Apache Struts 2.1.x and 2.3.x deployments utilizing the Struts 1 plugin (struts2-struts1-plugin)
Q3. What temporary mitigations or workarounds exist for CVE-2017-9791 before patching?
[Mitigation] Upgrade to the latest supported Apache Struts 2.5.x+ versions, or completely disable and remove the struts2-struts1-plugin dependency Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
Generate an Internal Engineering Notice or CISO Report for CVE-2017-9791
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