Critical ACF Extended Flaw (CVE-2025-13486, CVSS 9.8) Allows Unauthenticated RCE on 100K WordPress Sites

Estimated reading time: 8 minutes

Key takeaways:

  • A critical RCE vulnerability (CVE-2025-13486) affects the Advanced Custom Fields: Extended plugin.
  • Unauthenticated attackers can execute arbitrary code on over 100,000 WordPress sites.
  • Immediate updating to version 0.9.2 or later is crucial for mitigation.
  • Monitoring for suspicious activity and implementing a WAF are also recommended.
  • PurpleOps services can help organizations protect against this and similar vulnerabilities.

Table of contents:

  1. Unauthenticated RCE Vulnerability in ACF Extended: CVE-2025-13486
  2. Impact and Exploitation
  3. Remediation and Mitigation
  4. Technical Details and Analysis
  5. Practical Takeaways and Actionable Advice
  6. How This Relates to PurpleOps Services
  7. FAQ

A critical security vulnerability, identified as CVE-2025-13486 with a CVSS score of 9.8, has been discovered in the Advanced Custom Fields: Extended plugin for WordPress. This flaw allows unauthenticated attackers to execute arbitrary code remotely on over 100,000 websites. This blog post breaks down the vulnerability, its potential impact, and recommended steps to mitigate the risk.

Unauthenticated RCE Vulnerability in ACF Extended: CVE-2025-13486

The Advanced Custom Fields: Extended plugin is a popular WordPress utility used on a large number of websites. The cyber threat intelligence platform community has been actively monitoring this situation, and this vulnerability poses a significant risk due to the potential for unauthenticated remote code execution (RCE). This means an attacker can gain complete control over a website without needing any login credentials.

Security researcher dudekmar discovered the vulnerability and reported it through the Wordfence Bug Bounty Program, earning a substantial reward for the discovery given its severity. The core issue lies within the prepare_form() function of the plugin’s acfe_module_form_front_render class, which is responsible for rendering forms on the frontend of websites.

The vulnerability stems from the plugin’s insecure handling of user input during the form rendering process. The code uses the PHP function call_user_func_array, which executes a callback function with an array of parameters. The problem is that the data used in this function, including the function to be called, is directly supplied by the user without proper validation.

According to the technical analysis, the form[render] parameter retrieved from user input defines the function used to render the form, and the data passed to the function comes from the form parameter, also supplied via user input. The lack of input validation on the function call allows attackers to call arbitrary PHP functions. This makes arbitrary code injection possible, leading to the RCE vulnerability.

Impact and Exploitation

The implications of CVE-2025-13486 are severe. Because it’s an unauthenticated RCE flaw, attackers don’t need to log in to exploit it. This significantly lowers the barrier to entry and increases the potential for widespread attacks.

A prime example of how this vulnerability could be exploited is through privilege escalation. An attacker could use the wp_insert_user() function to create a new administrator user. Once administrative access is established, the attacker effectively owns the site. This level of access allows for complete site compromise through webshells and other malicious techniques. This level of breach detection is critical for mitigating damage after such an attack.

The ability to inject arbitrary code can lead to various malicious activities, including:

  • Data theft: Accessing and exfiltrating sensitive information stored on the website’s database.
  • Malware distribution: Uploading and distributing malware to website visitors.
  • Website defacement: Altering the website’s content to display malicious or unwanted information.
  • Backdoor installation: Creating persistent backdoors to maintain unauthorized access to the website.
  • Denial of Service (DoS): Disrupting the website’s availability by overwhelming it with traffic.

This vulnerability can be a gateway for real-time ransomware intelligence gathering as attackers can easily deploy ransomware on compromised servers.

Remediation and Mitigation

The developers of the Advanced Custom Fields: Extended plugin have addressed the vulnerability by completely removing the user input and call_user_func_array() function-based render part from the prepare_form() function.

Website administrators using the Advanced Custom Fields: Extended plugin are strongly advised to take the following actions:

  1. Update Immediately: Verify the installed version of the plugin and update to the latest patched version (0.9.2 or later) as soon as possible. This is the primary step to eliminate the vulnerability.
  2. Monitor for Suspicious Activity: Keep an eye on website logs for any unusual activity that might indicate a compromise. This includes unexpected file modifications, new user accounts, or unusual traffic patterns. Employing a dark web monitoring service can help detect if your website credentials have been compromised and are being sold or discussed on the dark web.
  3. Review User Accounts: Check for any newly created or unauthorized user accounts, especially those with administrative privileges.
  4. Implement a Web Application Firewall (WAF): A WAF can help to filter out malicious traffic and prevent exploitation attempts.
  5. Regular Security Audits: Conduct regular security audits and penetration testing to identify and address potential vulnerabilities before they can be exploited. Considering supply-chain risk monitoring is also important, as vulnerabilities in third-party plugins can pose a threat.

Technical Details and Analysis

The vulnerability’s core lies in the insecure use of the call_user_func_array() function. This function is powerful, allowing developers to call functions dynamically based on user input. However, when used without proper input validation, it can become a dangerous attack vector.

In this case, the form[render] parameter dictates which function is called, and the form parameter provides the arguments to that function. Because there are no restrictions on the function that can be called, an attacker can specify any PHP function available on the server, including those that allow for arbitrary code execution.

For example, an attacker could use the system() function to execute operating system commands directly on the server. This would give them complete control over the server and allow them to perform any action they desire. This illustrates the importance of underground forum intelligence in understanding how attackers might exploit vulnerabilities like this.

The fix implemented by the developers effectively removes the vulnerable code by eliminating the reliance on user-supplied input for the function call. This prevents attackers from injecting arbitrary code and mitigates the risk of RCE.

Practical Takeaways and Actionable Advice

For Technical Readers:

  • Code Review: Review code for instances of call_user_func_array() and other dynamic function calls. Ensure all input is properly validated and sanitized.
  • Input Validation: Implement strict input validation to prevent malicious code from being injected through user-supplied data.
  • Principle of Least Privilege: Apply the principle of least privilege to limit the permissions of user accounts and prevent attackers from gaining administrative access.
  • Web Application Firewall (WAF): Implement a WAF with updated rules to detect and block exploit attempts targeting this and other vulnerabilities. Regularly update WAF rules.
  • Vulnerability Scanning: Use automated vulnerability scanners to identify potential security flaws in your WordPress installation and plugins. Integrate this into your CI/CD pipeline.

For Non-Technical Readers (Business Leaders):

  • Prioritize Updates: Ensure your website administrators prioritize applying security updates and patches promptly.
  • Security Awareness Training: Provide security awareness training to employees to help them identify and avoid phishing attacks and other social engineering tactics.
  • Incident Response Plan: Develop and maintain an incident response plan to effectively handle security breaches and minimize damage.
  • Regular Backups: Maintain regular backups of your website and database to facilitate recovery in case of a compromise.
  • Security Assessment: Engage a cybersecurity firm to conduct a comprehensive security assessment of your website and identify potential vulnerabilities.

How This Relates to PurpleOps Services

PurpleOps provides a range of services that can help organizations protect themselves from vulnerabilities like CVE-2025-13486. Our offerings include:

  • Cyber Threat Intelligence: PurpleOps provides comprehensive cyber threat intelligence services, including monitoring of underground forums and the dark web, to identify emerging threats and vulnerabilities. We provide a live ransomware API to stay ahead of ransomware attacks.
  • Vulnerability Management: We offer vulnerability scanning and assessment services to identify and prioritize security flaws in your systems.
  • Penetration Testing: Our penetration testing services simulate real-world attacks to identify and exploit vulnerabilities in your website and applications. This can include targeted red team operations to test your defenses.
  • Managed Security Services: PurpleOps provides managed security services, including breach detection, WAF management, and incident response, to help organizations maintain a strong security posture.
  • Supply Chain Security: We offer services to assess and manage the security risks associated with your third-party vendors and suppliers.
  • Dark Web Monitoring: Leveraging advanced techniques for telegram threat monitoring, we scan the dark web for mentions of your organization, compromised credentials, and leaked data. Brand leak alerting ensures you are immediately notified of any sensitive information being exposed.

By leveraging PurpleOps services, organizations can proactively identify and address vulnerabilities, strengthen their security posture, and minimize the risk of successful cyberattacks. Consider our solutions for supply-chain information security to protect your entire ecosystem.

To learn more about how PurpleOps can help you protect your organization from cyber threats, explore our platform or contact us for more information about our PurpleOps Solutions.

FAQ

Q: What is CVE-2025-13486?
A: CVE-2025-13486 is a critical remote code execution (RCE) vulnerability in the Advanced Custom Fields: Extended plugin for WordPress.

Q: What is the impact of this vulnerability?
A: This vulnerability allows unauthenticated attackers to execute arbitrary code remotely on affected websites, potentially leading to data theft, malware distribution, and complete site compromise.

Q: How can I protect my website from this vulnerability?
A: Update the Advanced Custom Fields: Extended plugin to version 0.9.2 or later, monitor for suspicious activity, review user accounts, implement a Web Application Firewall (WAF), and conduct regular security audits.