Everest Forms (Pro) <= 1.9.7 - Unauthenticated PHP Object Injection via PHAR Deserialization in Form Signature
Strategic Overview
- Status
- Patched in 1.9.8
- Affected Plugin
- Everest Forms Pro
- Affected Version
<= 1.9.7- CVSS
- 5.6Medium
- Weakness type
- CWE-502 · Deserialization of Untrusted Data
- CVE
CVE-2025-8871
At a glance
CVE-2025-8871 is a medium-severity Deserialization of Untrusted Data vulnerability in the Everest Forms Pro WordPress plugin, affecting versions <= 1.9.7. It carries a CVSS score of 5.6 (reachable over the network). Exploitation requires no authentication. The issue is fixed in version 1.9.8; sites on affected versions should update now. Disclosed November 2025, reported by Alex Thomas.
Vulnerability Overview
The Everest Forms (Pro) plugin for WordPress is vulnerable to PHP Object Injection in all versions up to, and including, 1.9.7 via deserialization of untrusted input in the mime_content_type() function. This makes it possible for unauthenticated attackers to inject a PHP Object. This vulnerability may be exploited by unauthenticated attackers when a form is present on the site with a non-required signature form field along with an image upload field. No known POP chain is present in the vulnerable software, which means this vulnerability has no impact unless another plugin or theme containing a POP chain is installed on the site. If a POP chain is present via an additional plugin or theme installed on the target system, it may allow the attacker to perform actions like delete arbitrary files, retrieve sensitive data, or execute code depending on the POP chain present. This vulnerability is only exploitable in PHP versions prior to 8.
Technical Analysis
The vector marks this flaw as remotely reachable over the network, and no privileges on the target site, and no interaction from a victim user.
CWE-502: Deserialization of Untrusted Data
Everest Forms Pro <= 1.9.7 carries this weakness at mime_content_type(), and reaching it takes no account at all. Deserialization of untrusted data means the application reconstructs objects from input a caller controls, letting the attacker choose which classes get instantiated and what their properties hold.
A workable chain turns deserialization into file writes, deletions or code execution, depending on what the loaded classes do in their magic methods. For Everest Forms Pro the fix is 1.9.8: builds <= 1.9.7 are affected, anything from 1.9.8 onward is not.
Remediation
Update to version 1.9.8, or a newer patched version
How does WordSec protect against this?
Requests carrying this pattern arrive without a session, so nothing upstream of the firewall gets a chance to reject them: WordSec's web application firewall inspects request payloads before WordPress loads them. Classes like this one can leave something behind, so the staged malware scanner is the second half: it looks for dropped files and modified code rather than for the request that created them. None of that substitutes for the fix: Everest Forms Pro 1.9.8 closes this, and updating the plugin is the step that ends it.
- Firewall
- Scanner
- Login Security
External References
Related records
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