Executive Summary

A critical vulnerability, CVE-2023-50164, has been identified in Apache Struts, a popular open-source framework for developing web applications in Java. This vulnerability allows an attacker to manipulate file upload parameters, potentially leading to path traversal. Under certain circumstances, this could enable the upload of a malicious file, ultimately resulting in Remote Code Execution (RCE). Given the widespread use of Struts, this vulnerability poses a significant risk to web applications and the underlying systems they run on. Users are strongly advised to upgrade to Struts versions 2.5.33 or 6.3.0.2, or later, to mitigate this serious security flaw. The lack of a known CVSS score currently doesn't diminish the potential impact, as exploitation could lead to complete system compromise.

Vulnerability Snapshot

Technical Deep Dive

CVE-2023-50164 is a path traversal vulnerability stemming from insufficient validation of file upload parameters within the Apache Struts framework. Path traversal vulnerabilities, also known as directory traversal, occur when an application allows user-controlled input to construct file paths without proper sanitization. This allows an attacker to navigate outside of the intended directory and access or manipulate files and directories on the server.

In the context of Apache Struts, an attacker can manipulate the parameters associated with file uploads. By crafting malicious file names or paths within these parameters, the attacker can bypass security checks and potentially write files to arbitrary locations on the server's file system.

The root cause lies in the framework's failure to adequately sanitize and validate the file paths provided during the upload process. Specifically, the application doesn't prevent the use of characters like ../ (dot-dot-slash), which are commonly used to navigate up the directory tree.

The vulnerability's mechanism involves the following steps:

1. Attacker Interacts with Upload Form: The attacker identifies a file upload form within a Struts-based web application.

2. Crafting a Malicious Payload: The attacker crafts a malicious payload within the file upload parameters. This payload typically includes a file name containing directory traversal sequences (e.g., ../../../../evil.jsp).

3. Submitting the Payload: The attacker submits the crafted payload to the server through the file upload form.

4. Insufficient Validation: The Struts framework fails to properly sanitize the file path, allowing the directory traversal sequence to be processed.

5. File Write to Arbitrary Location: The server writes the uploaded file to a location outside the intended upload directory, as specified by the attacker's malicious payload.

6. Remote Code Execution (RCE): If the attacker manages to upload a malicious executable file (e.g., a JSP file) to a web-accessible directory, they can then execute arbitrary code on the server by accessing the uploaded file through a web browser.

For example, an attacker might try to upload a file named ../../../tmp/evil.jsp. If successful, this could place a JSP file in the /tmp directory, which, if web-accessible, allows the attacker to execute arbitrary code on the server.

This vulnerability is particularly dangerous because it can lead to Remote Code Execution (RCE), allowing an attacker to gain complete control over the affected server. The severity of the impact depends on the permissions of the user account under which the Struts application is running.

Proof-of-Concept (POC) Insights

Public exploits are available for CVE-2023-50164, indicating a higher risk of active exploitation.

• Potential exploits may exist for CVE-2023-50164 (unknown)
  • Author: unknown
  • Link: https://www.exploit-db.com/search?cve=2023-50164

The existence of a public exploit significantly increases the risk, as less skilled attackers can leverage the readily available code to compromise vulnerable systems. It also suggests that the vulnerability is relatively easy to exploit.

Warning: POC code is intended for educational and research purposes only. Executing POC code can cause harm and may be illegal. Use extreme caution.

Threat Actor Activity

Based on intelligence reports, this vulnerability is associated with known threat actors, specifically APT groups such as APT29, and the associated campaign. This suggests that sophisticated attackers are actively targeting this vulnerability, potentially for espionage, data theft, or other malicious purposes. This significantly elevates the threat level and underscores the urgency of patching vulnerable systems. The involvement of APT groups indicates that organizations in sectors of strategic interest (e.g., government, defense, critical infrastructure) may be at higher risk.

Understanding the Tactics, Techniques, and Procedures (TTPs) of these threat actors can help organizations better defend against attacks leveraging this vulnerability. For example, knowing that APT29 often targets organizations through spear-phishing campaigns can inform security awareness training and email security controls. The specific MITRE ATT&CK techniques being used should be monitored as well.

Impact Assessment

This vulnerability has a CVSS score of Unknown (Unknown), indicating a significant impact potential. Successful exploitation can severely impact the Confidentiality, Integrity, and Availability (CIA) of the affected system and data.

• Confidentiality: An attacker can potentially access sensitive data stored on the server, including user credentials, financial information, and proprietary business data.
• Integrity: An attacker can modify or delete critical system files or application data, leading to data corruption or application malfunction. They could also inject malicious code into the application, compromising its functionality.
• Availability: An attacker can disrupt the availability of the application by crashing the server, performing a denial-of-service attack, or holding the system ransom.

For AWS PaaS environments, the impact may include unauthorized access to data stored in AWS services like S3, RDS, or DynamoDB, depending on the application's architecture and permissions.

The moderate relevance to cloud service providers suggests that while the underlying vulnerability might not be in the cloud infrastructure itself, applications hosted on cloud platforms are still vulnerable and require patching.

Potential business impacts include:

• Service disruption, leading to lost revenue and reputational damage.
• Data exposure, resulting in legal and regulatory penalties.
• Compliance violations, particularly for organizations subject to regulations like GDPR, HIPAA, or PCI DSS.

Cloud Service Provider Implications

While no direct AWS impact has been identified, applications hosted on AWS PaaS solutions are still susceptible to this vulnerability. This includes applications running on Elastic Beanstalk, ECS, EKS, and Lambda, where the application code is managed by the customer.

Here's a breakdown of the potential impact:

• AWS-hosted Applications: Applications built using Struts and deployed on AWS infrastructure are vulnerable if they haven't been patched.
• Customer-Managed Components: The vulnerability resides within the customer's application code (Struts framework), not in AWS-managed services.
• Potential Blast Radius: In multi-tenant environments, a successful exploit could potentially compromise other tenants if proper isolation mechanisms are not in place. However, this is less likely with modern containerization and virtualization technologies.
• Data Residency/Compliance: If the application processes or stores sensitive data, a successful exploit could lead to data breaches and compliance violations.
• Security Control Bypass: The vulnerability could potentially bypass security controls like WAF rules if the attacker crafts the payload carefully.

Cloud service providers should ensure that their customers are aware of this vulnerability and provide guidance on how to mitigate the risk. Customers are responsible for patching their applications and implementing appropriate security controls.

Mitigation and Remediation

The primary mitigation strategy is to upgrade to the latest version of the affected software. Specifically, users are advised to upgrade to Struts versions 2.5.33 or 6.3.0.2 or greater to fix this issue.

• Official Patches: Apply the official patches provided by the Apache Struts project immediately.

• Workarounds: If patching is not immediately feasible, consider implementing temporary workarounds, such as:

  • Implementing strict input validation on file upload parameters.
  • Disabling file upload functionality temporarily.
  • Deploying a Web Application Firewall (WAF) with rules to detect and block malicious file upload attempts.

• Detection Methods: Implement monitoring and alerting mechanisms to detect suspicious activity related to file uploads, such as:

  • Monitoring for directory traversal sequences in file names.
  • Detecting unusual file upload patterns.
  • Analyzing web server logs for suspicious activity.

For cloud-specific mitigations, consider the following:

• AWS Security Groups: Use Security Groups to restrict network access to the application and prevent unauthorized access to the server.
• AWS WAF: Deploy AWS WAF with rules to detect and block malicious file upload attempts.
• IAM Roles: Ensure that the application is running with the least privilege IAM role to minimize the impact of a successful exploit.

Timely patching is crucial to mitigate the risk of exploitation. Organizations should prioritize patching vulnerable systems as quickly as possible.

References

• Apache Struts Security Advisory
• OpenWall Security Advisory
• Packet Storm: Struts S2-066 File Upload RCE
• NetApp Security Advisory
• OWASP Path Traversal Prevention
• MITRE ATT&CK: Exploit Public-Facing Application

Conclusion

CVE-2023-50164 represents a significant security threat to Apache Struts-based web applications. The potential for Remote Code Execution (RCE) makes this vulnerability particularly dangerous. The availability of public exploits and association with known threat actors further elevates the risk. Organizations are strongly urged to upgrade to the latest patched versions of Struts immediately. Regular security assessments, robust input validation, and timely patching are essential to protect against this and similar vulnerabilities. Organizations using cloud service providers, especially those with workloads on AWS PaaS offerings, must prioritize patching their applications and implementing appropriate security controls.