CVE-2025-8871 Overview
CVE-2025-8871 is a PHP Object Injection vulnerability in the Everest Forms (Pro) plugin for WordPress. The flaw affects all versions up to and including 1.9.7. It stems from deserialization of untrusted input in the mime_content_type() function call path. Unauthenticated attackers can inject a PHP object when a form contains a non-required signature field alongside an image upload field. The vulnerability requires PHP versions prior to 8 to be exploitable. This weakness is classified as insecure deserialization [CWE-502].
Critical Impact
No known Property-Oriented Programming (POP) chain exists in the plugin itself. Exploitation requires a POP chain from another installed plugin or theme, which could enable arbitrary file deletion, sensitive data retrieval, or code execution.
Affected Products
- Everest Forms (Pro) plugin for WordPress, versions up to and including 1.9.7
- WordPress sites running PHP versions prior to 8.0
- WordPress installations with forms containing both signature and image upload fields
Discovery Timeline
- 2025-11-05 - CVE-2025-8871 published to the National Vulnerability Database (NVD)
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-8871
Vulnerability Analysis
The vulnerability resides in the Everest Forms (Pro) plugin's handling of file uploads combined with signature form fields. When a form containing a non-required signature field and an image upload field is submitted, the plugin passes untrusted input to the mime_content_type() function in a way that triggers PHP object deserialization. Attackers who supply crafted serialized PHP data can instantiate arbitrary objects within the WordPress process.
The plugin itself contains no exploitable POP chain. The impact depends entirely on other installed plugins or themes that expose gadget chains through magic methods such as __destruct() or __wakeup(). Real-world WordPress environments commonly bundle multiple plugins, making chain discovery plausible on targeted sites.
Exploitation is limited to PHP versions before 8.0. PHP 8 changed how mime_content_type() and related file-handling functions process inputs, breaking the deserialization sink used in this attack path.
Root Cause
The root cause is insecure deserialization of user-controlled input reaching a PHP function that triggers object instantiation on serialized payloads. The plugin fails to validate or sanitize the file metadata before passing it into a code path that performs unserialize() semantics on attacker-supplied bytes.
Attack Vector
An unauthenticated remote attacker submits a crafted form request to a WordPress site running a vulnerable Everest Forms configuration. The request must target a form that includes an image upload field and an optional signature field. The attacker embeds a serialized PHP object in the upload payload. When the plugin invokes mime_content_type() on the input, PHP deserializes the attacker's object. If a POP chain exists in another installed component, the object's lifecycle methods execute attacker-controlled logic.
No authentication or user interaction is required. However, exploitation depends on multiple prerequisites, which contributes to the high attack complexity rating.
Detection Methods for CVE-2025-8871
Indicators of Compromise
- POST requests to Everest Forms submission endpoints containing serialized PHP object markers such as O: or a: in upload field values
- Unexpected file creation, deletion, or modification following form submissions on WordPress sites
- PHP error log entries referencing unserialize() failures or unexpected class instantiation from form handlers
Detection Strategies
- Inspect WordPress access logs for form submissions containing image uploads with anomalous MIME metadata or serialized payload signatures
- Audit installed Everest Forms plugin versions across managed WordPress deployments and flag any at or below 1.9.7
- Correlate form submission events with subsequent unusual PHP process behavior, file system changes, or outbound network activity
Monitoring Recommendations
- Enable verbose logging on WordPress form handlers and forward logs to a centralized SIEM for correlation
- Monitor PHP process spawning and file operations on web servers hosting WordPress
- Track plugin inventory across the WordPress fleet and alert on outdated Everest Forms installations
How to Mitigate CVE-2025-8871
Immediate Actions Required
- Update the Everest Forms (Pro) plugin to a version above 1.9.7 as soon as a patched release is available from the vendor
- Audit all forms for the vulnerable combination of signature and image upload fields and disable affected forms until patched
- Upgrade PHP to version 8.0 or later, which eliminates the exploitable deserialization path
Patch Information
Refer to the Everest Forms Changelog for the vendor's official release notes and patched version details. Additional technical context is available in the Wordfence Vulnerability Report.
Workarounds
- Remove signature form fields or set them as required to break the exploitation prerequisites
- Remove image upload fields from forms that also contain signature fields until the plugin is patched
- Deploy a Web Application Firewall (WAF) rule to block form submissions containing serialized PHP object patterns
- Uninstall unused plugins and themes to reduce the likelihood that a POP chain is available on the site
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
