CVE-2026-62103: Everest Forms PHP Object Injection Flaw

CVE-2026-62103 Overview

CVE-2026-62103 is an unauthenticated PHP Object Injection vulnerability in the Everest Forms WordPress plugin, affecting versions up to and including 3.6.0. The flaw is classified under [CWE-502] Deserialization of Untrusted Data. Attackers can send crafted input over the network without authentication or user interaction, triggering unsafe deserialization inside the plugin.

When combined with a suitable gadget chain from WordPress core or another installed plugin, this class of vulnerability enables arbitrary code execution, file operations, or data tampering on the target site.

Critical Impact
Unauthenticated attackers can inject serialized PHP objects into vulnerable Everest Forms installations, potentially leading to remote code execution and full site compromise.

Affected Products

Everest Forms WordPress plugin versions <= 3.6.0
WordPress sites with the Everest Forms plugin installed and network-reachable
Multi-site WordPress deployments where the plugin is network-activated

Discovery Timeline

2026-09-11 - CVE-2026-62103 published to the National Vulnerability Database (NVD)
2026-09-11 - Last updated in NVD database

Technical Details for CVE-2026-62103

Vulnerability Analysis

The vulnerability stems from unsafe handling of serialized PHP data within Everest Forms <= 3.6.0. PHP Object Injection occurs when user-controllable input is passed to unserialize() or an equivalent deserialization routine without validation. The plugin exposes this sink on a code path reachable by unauthenticated requests.

During deserialization, PHP reconstructs objects and triggers magic methods such as __wakeup(), __destruct(), or __toString(). If a class defined in WordPress core, Everest Forms, or another loaded plugin contains exploitable logic in one of these methods, an attacker can build a POP (Property-Oriented Programming) chain to abuse it.

The attack requires no privileges and no user interaction. Exploitation depends on the presence of a usable gadget chain in the target environment, which is common on typical WordPress installations that load multiple plugins and themes.

Root Cause

The root cause is deserialization of untrusted data [CWE-502]. The plugin accepts attacker-controlled serialized input and reconstructs PHP objects from it without integrity checks or an allowlist of expected classes. This design lets attacker-supplied class instances re-enter the application state.

Attack Vector

An unauthenticated remote attacker sends a crafted HTTP request containing a serialized PHP payload to a vulnerable Everest Forms endpoint. The plugin deserializes the payload, instantiating attacker-chosen classes and invoking their magic methods. Depending on the available gadget chain, this can lead to arbitrary file write, arbitrary file read, SQL manipulation, or remote code execution.

For technical specifics on the vulnerable code path, see the Patchstack Everest Forms vulnerability entry.

Detection Methods for CVE-2026-62103

Indicators of Compromise

HTTP requests to Everest Forms endpoints containing serialized PHP markers such as O:, a:, or s: followed by class or property definitions
Unexpected files created under wp-content/uploads/ or theme directories following form submissions
New or modified PHP files in the WordPress installation, especially webshells or files with obfuscated content
Outbound network connections from the web server process to attacker-controlled infrastructure

Detection Strategies

Inspect web server and WAF logs for POST bodies to Everest Forms endpoints containing serialized object patterns
Monitor PHP error logs for __wakeup, __destruct, or unserialize warnings originating from Everest Forms code paths
Baseline plugin file integrity and alert on modifications to WordPress core, Everest Forms, or other plugin files
Correlate form submission events with subsequent process execution or file system changes on the host

Monitoring Recommendations

Deploy runtime monitoring on WordPress hosts to detect anomalous child processes spawned from PHP-FPM or Apache workers
Enable audit logging for administrative actions, user creation, and option changes within WordPress
Aggregate web, PHP, and host telemetry into a central data lake to support cross-source hunting for exploitation chains

How to Mitigate CVE-2026-62103

Immediate Actions Required

Update Everest Forms to a version later than 3.6.0 that addresses this vulnerability as identified in the vendor advisory
Audit WordPress installations for indicators of exploitation, including unexpected admin users, modified files, and unfamiliar scheduled tasks
Restrict access to WordPress form submission endpoints using a web application firewall until patching is complete
Rotate WordPress secrets in wp-config.php and reset administrator credentials if compromise is suspected

Patch Information

Refer to the Patchstack advisory for Everest Forms for the fixed version and remediation guidance. Apply the vendor-supplied update through the WordPress plugin manager or via managed hosting update workflows.

Workarounds

Temporarily deactivate the Everest Forms plugin on affected sites until the patch is applied
Deploy WAF rules that block requests containing serialized PHP object signatures on plugin endpoints
Restrict PHP disable_functions and file permissions to reduce the impact of a successful gadget chain execution

bash

# Example WAF rule concept: block serialized PHP object patterns in POST bodies
# ModSecurity rule (illustrative)
SecRule REQUEST_URI "@contains /wp-admin/admin-ajax.php" \
  "chain,phase:2,deny,status:403,id:1002026,msg:'Potential PHP Object Injection - CVE-2026-62103'"
  SecRule REQUEST_BODY "@rx O:[0-9]+:\"[A-Za-z_\\\\]+\":[0-9]+:" \
    "t:none,t:urlDecodeUni"