Plugin-navn	Type of Vulnerability	CVE Number	Hastighed	CVE Publish Date	Source URL
Avancerede brugerdefinerede felter	Remote Code Inclusion (RCI)	CVE-2014-4114	Høj	2025-08-05	View Source

Critical Remote Code Execution Vulnerability Discovered in Advanced Custom Fields Plugin (<= 3.5.1) – What WordPress Site Owners Must Know

The WordPress ecosystem thrives on plugins that extend its functionality, offering everything from simple tweaks to complex integrations. However, with great power comes great responsibility—particularly on the security front. Recently, a significant vulnerability has been uncovered in the widely-used Advanced Custom Fields (ACF) plugin, versions up to and including 3.5.1, exposing millions of websites to remote code execution (RCE) risks through remote file inclusion.

As a dedicated WordPress security and firewall provider, we are committed to helping WordPress site owners understand this threat, its implications, and the critical steps they must take to protect their sites effectively.

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Understanding the Vulnerability: Remote Code Execution via Remote File Inclusion in ACF (<= 3.5.1)

At its core, this vulnerability allows a remote attacker to execute arbitrary code on an affected WordPress site by exploiting the remote file inclusion (RFI) flaw in the Advanced Custom Fields plugin. Remote file inclusion is when an unauthorized actor tricks the system into loading and executing malicious code hosted on an external location. This can pave the way for complete site takeover—allowing attackers to install backdoors, steal sensitive data, deface the site, or use the website as a launchpad for further attacks.

• Sårbare versioner: All ACF plugin versions up to and including 3.5.1.
• Fixed In: Version 3.5.2 and later.
• Programrettelsesprioritet: Medium (but to be treated as critical due to the nature of RCE).
• CVSS-score: 3.8 (Medium severity, noting real-world impact may vary but should not be underestimated).
• Classification: Remote Code Execution (RCE), which ranks as one of the most severe security vulnerabilities for any web property.

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Why Remote Code Execution Should Alarm Every WordPress Administrator

Many WordPress users might underestimate medium-rated vulnerabilities, yet Remote Code Execution stands apart as an exceptionally dangerous type of security flaw because:

1. Complete Server Control: Attackers can execute any command, load malicious code, and modify site files arbitrarily.
2. Backdoor Creation: Once access is gained, malicious actors can install persistent backdoors, making eradication challenging.
3. Datatyveri: Sensitive customer and site data can be exfiltrated silently.
4. Distribution of Malware: The infected website can be turned into a spam or malware distribution hub.
5. Reputation Damage & SEO Blacklisting: Search engines may blacklist compromised sites, adversely affecting traffic and revenue.

The exploitation of this flaw is not theoretical—such vulnerabilities are actively sought and abused by automated scanning bots and threat actors targeting unpatched WordPress sites globally.

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How Does This Vulnerability Exploit Work in the ACF Plugin?

Without diving too deeply into code, attackers leverage the plugin’s failure to adequately validate and sanitize user-supplied input that references external files. This results in the inclusion of remote files, which contain malicious PHP code, executing under the context of the WordPress server.

This exploitation technique bypasses many traditional security controls because:

• It abuses plugin logic assumed safe by site administrators.
• Triggers execution at the WordPress application level, not at lower network layers.
• Can be initiated via simple HTTP requests, requiring no authentication or privileged access.

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Who Is at Risk?

• Sites using Advanced Custom Fields plugin at version 3.5.1 or below: If your site employs this plugin and hasn’t been updated, your site is directly vulnerable.
• Multi-site WordPress installations: Risk gets heightened because a breach in one site can potentially impact others in the network.
• Sites without a strong WAF or virtual patching: Without a protective web application firewall or rapid virtual patching, automated attacks can succeed near instantly after vulnerability disclosure.
• Sites relying solely on plugin updates without proactive monitoring: Attackers exploit the window between vulnerability publication and patching.

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Steps to Mitigate and Secure Your WordPress Site Against This Vulnerability

1. Update the Plugin Immediately

The absolute first line of defense is upgrading ACF to version 3.5.2 or later. This patch addresses the remote file inclusion issue and closes the attack vector.

• Naviger til dit WordPress-dashboard.
• Gå til Plugins > Installerede plugins.
• Locate Avancerede brugerdefinerede felter, then update to the latest version.

Note: Always back up your website before performing updates.

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2. Enable Automatic Updates for Vulnerable Plugins

Keeping plugins current can be challenging, especially for busy site owners. Enabling automatic updates ensures critical patches like this one are applied swiftly without manual intervention.

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3. Employ a Robust WordPress Web Application Firewall (WAF)

A WAF plays a crucial role by:

• Blocking exploit payloads targeting plugin vulnerabilities.
• Detecting abnormal file inclusion or execution attempts.
• Providing virtual patching—an immediate firewall-based patch for vulnerabilities even before official plugin updates are applied.

Without a firewall, sites remain exposed for longer periods after vulnerability disclosures, increasing exploitation risk.

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4. Conduct Regular Malware Scanning and Security Audits

Since RCE attacks often leave backdoors or malware behind:

• Perform thorough malware scans frequently.
• Utilize tools specialized in scanning WordPress environments.
• Schedule security audits to assess broader site health.

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5. Harden Your WordPress Environment

Complement plugin updates with best practices like:

• Disabling PHP execution in writable directories (uploads, cache).
• Securing wp-config.php and other core files.
• Utilizing least privilege principles for users and roles.
• Ensuring your hosting environment is secure and up to date.

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What If Your Site Has Already Been Compromised?

If you suspect exploitation of this vulnerability has already occurred (e.g., unexpected admin accounts, suspicious files, or unusual traffic patterns), do the following:

• Contact your hosting provider immediately for server-side malware scanning and restoration assistance.
• Engage a professional WordPress incident response service to clean and secure your site thoroughly.
• Reset all admin user passwords and review user activity.
• Review logs for suspicious activity and remove unauthorized code or users.
• Avoid relying only on plugin-level malware scanners because advanced threats often evade or disable these tools.

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The Bigger Picture: Why Attackers Target WordPress Sites Like Yours

Attackers rely on opportunistic scanning techniques to find vulnerable plugins or themes. Once a vulnerability is public (like this ACF one), automated bots ramp up exploit attempts rapidly, targeting:

• Websites with unpatched or outdated plugins.
• Sites lacking sufficient security controls.
• High traffic or business-critical websites for maximum impact.

No site is “too small” or “too niche” to be a target. The volume of WordPress websites makes every vulnerable installation a potential jackpot for cybercriminals.

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Leveraging Virtual Patching to Defend Your Site Between Updates

One of the most effective mitigation measures is virtuel patching, which secures your site via firewall rules preventing attacks that target known vulnerabilities before an official plugin update is applied.

Benefits of virtual patching:

• Provides immediate protection on disclosure of vulnerability.
• Does not delay site uptime or require manual updates.
• Minimizes risk exposure window.
• Works alongside existing security tools and hosting environments.

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Advanced Security Monitoring: Staying One Step Ahead

Security never rests. Proactively monitor your WordPress sites for emerging vulnerabilities, suspicious behaviors, and unusual access patterns. Integrating real-time threat intelligence, combined with automated mitigation, is essential to defending modern websites.

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Introducing WP-Firewall: Essential Protection Starts With Us

At WP-firewall, we understand the urgent need to act decisively on vulnerabilities like this. Our Grundlæggende gratis plan offers WordPress site owners essential defense tools to safeguard against critical threats:

• Managed firewall rules that adapt to emerging vulnerabilities.
• Unlimited bandwidth and Web Application Firewall (WAF) protection.
• Automated malware scanner identifying infected files and risky behaviors.
• Mitigation of OWASP Top 10 risks, including injection flaws like Remote Code Execution.

Getting started is fast, easy, and free—so you can fortify your website without delay.

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Why Every WordPress Owner Should Consider Our Security Plans

Beyond the free tier, our Standard Plan adds automatic malware removal and IP blacklisting/whitelisting capabilities for more granular control.

Vores Pro Plan unlocks monthly security reports, auto vulnerability virtual patching, and access to premium add-ons including:

• Dedicated account management.
• WordPress optimization services.
• Managed WordPress and security support tokens.

Building a layered defense with WP-Firewall significantly reduces your risk exposure and ensures your WordPress site stays resilient in an ever-evolving threat landscape.

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Summary: Take Proactive Steps Today to Secure WordPress Sites Using ACF

Key Points	Handling påkrævet
ACF plugin versions <= 3.5.1	Update immediately to version 3.5.2 or newer.
Remote Code Execution risk	Treat as critical; don’t delay patching.
Vulnerability type	Remote File Inclusion enabling rogue PHP execution
Risk of automated exploitation	High – attackers scan widely for these flaws.
Afbødning	Use managed firewall, virtual patching, and malware scanning
Compromised site?	Engage professional cleanup and hosting support

Security is a continuous journey, not a one-time fix. Stay vigilant, patch fast, and utilize protective tools designed with WordPress security expertise.

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Strengthen Your WordPress Security Foundation with WP-Firewall’s Free Plan

Take control of your website’s security today by joining thousands of WordPress users who rely on WP-Firewall to keep their sites safe and performant. Our no-cost Basic Plan equips you with the essential tools needed to:

• Proactively block attacks targeting vulnerable plugins like ACF.
• Scan for malware risks without burdening your server.
• Mitigate the top 10 most pervasive WordPress security threats.

Secure your WordPress website now with WP-Firewall’s free protection and experience peace of mind knowing your site is guarded by state-of-the-art defense mechanisms built specifically for WordPress.

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Afsluttende tanker

In the dynamic WordPress landscape, security challenges evolve constantly. The recent RCE vulnerability in the Advanced Custom Fields plugin is a stark reminder why site owners must remain proactive and informed.

• Don’t wait for an incident—update your plugins promptly.
• Implement a robust security posture that includes firewalls, scanning, and monitoring.
• Choose solutions that offer rapid protection, including virtual patching capabilities.

By taking these responsible actions, you ensure the longevity, safety, and trustworthiness of your WordPress site for visitors, customers, and your online reputation.

Stay safe, update early, and keep your WordPress sites solid.

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Written by: A WordPress Security Expert at WP-Firewall
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