CVE-2023-28782: Gravity Forms Deserialization Vulnerability

CVE-2023-28782 Overview

CVE-2023-28782 is a PHP Object Injection vulnerability in the Gravity Forms plugin for WordPress, developed by Rocketgenius Inc. The flaw is a Deserialization of Untrusted Data weakness [CWE-502] affecting Gravity Forms versions up to and including 2.7.3. An unauthenticated attacker can submit crafted serialized payloads over the network, triggering insecure deserialization within the plugin. Successful exploitation can lead to arbitrary code execution, data tampering, or full compromise of the underlying WordPress site.

Critical Impact

Unauthenticated PHP object injection enables remote code execution and full site compromise on vulnerable WordPress installations running Gravity Forms <= 2.7.3.

Affected Products

• Rocketgenius Gravity Forms plugin for WordPress
• Gravity Forms versions from n/a through 2.7.3
• WordPress sites using Gravity Forms with publicly reachable form endpoints

Discovery Timeline

• 2023-12-20 - CVE-2023-28782 published to NVD
• 2026-04-28 - Last updated in NVD database

Technical Details for CVE-2023-28782

Vulnerability Analysis

The vulnerability is an Insecure Deserialization issue in Gravity Forms. The plugin passes attacker-controlled input into PHP's deserialization routines without validating the source or contents of the serialized data. When PHP deserializes the payload, magic methods such as __wakeup() or __destruct() execute on reconstructed objects. If a suitable gadget chain exists in the WordPress core, the active theme, or any installed plugin, the attacker can pivot deserialization into arbitrary code execution. The attack requires no authentication and no user interaction, and it can be delivered over the network against any reachable Gravity Forms endpoint.

Root Cause

The root cause is the use of unserialize() on untrusted input within the plugin's request handling logic. PHP's native deserialization mechanism reconstructs objects of arbitrary classes and invokes their magic methods, which makes it unsafe for processing data that may originate from clients. Gravity Forms <= 2.7.3 does not enforce allow-listed classes or use a safe serialization format such as JSON for affected code paths.

Attack Vector

An unauthenticated remote attacker submits a crafted request to a Gravity Forms endpoint that triggers deserialization of a serialized PHP object. The payload references a gadget chain present in the WordPress runtime. Once instantiated, the chain executes attacker-chosen operations such as writing files, executing system commands, or modifying database records. The attack surface includes any site that exposes Gravity Forms processing to anonymous visitors.

No verified public proof-of-concept code is available. See the Patchstack Vulnerability Advisory for advisory-level technical detail.

Detection Methods for CVE-2023-28782

Indicators of Compromise

• HTTP POST requests to Gravity Forms endpoints containing serialized PHP markers such as O:, a:, or s: followed by class and property declarations.
• Unexpected new PHP files in wp-content/uploads/, wp-content/plugins/, or theme directories following form submissions.
• New or modified WordPress administrator accounts created without a corresponding admin login event.
• Outbound network connections from the PHP-FPM or web server process to unfamiliar hosts shortly after form submissions.

Detection Strategies

• Inspect web server access logs for request bodies or query strings containing serialized object signatures targeting Gravity Forms paths.
• Compare the installed Gravity Forms version against 2.7.3; any version at or below this is vulnerable.
• Use a web application firewall ruleset that flags PHP object injection patterns in request parameters.
• Run file integrity monitoring on the WordPress directory to detect unexpected PHP file additions or modifications.

Monitoring Recommendations

• Forward WordPress, PHP error, and web server logs to a centralized logging or SIEM platform for correlation.
• Alert on web server processes spawning shell interpreters such as sh, bash, or cmd.exe.
• Monitor for privilege changes within the wp_users and wp_usermeta tables.
• Track plugin and theme file modification timestamps to surface tampering after exploitation attempts.

How to Mitigate CVE-2023-28782

Immediate Actions Required

• Upgrade Gravity Forms to version 2.7.4 or later on every WordPress site where the plugin is installed.
• Audit affected sites for indicators of compromise, including unexpected admin accounts, modified plugin files, and webshells in upload directories.
• Rotate WordPress administrator passwords, API keys, and any secrets stored within the site database if compromise is suspected.
• Place a web application firewall in front of WordPress to filter PHP object injection patterns until patching is complete.

Patch Information

Rocketgenius addressed the deserialization flaw in Gravity Forms versions after 2.7.3. Administrators must update the plugin through the WordPress dashboard or by deploying the vendor-supplied package. Refer to the Patchstack Vulnerability Advisory for the fixed version and advisory details.

Workarounds

• Disable and remove the Gravity Forms plugin on sites that cannot be patched immediately.
• Restrict access to Gravity Forms submission endpoints using IP allow-lists or authentication where the business workflow allows.
• Deploy WAF rules that block requests containing PHP serialized object signatures such as O:<digits>:" in untrusted parameters.
• Run PHP with the latest stable version and disable unused extensions to reduce the available gadget chain surface.

# Example WAF/ModSecurity rule to block PHP object injection patterns
SecRule ARGS|REQUEST_BODY "@rx O:[0-9]+:\"[a-zA-Z_\\\\]+\":[0-9]+:" \
    "id:1002820,\
     phase:2,\
     deny,\
     status:403,\
     log,\
     msg:'Potential PHP Object Injection - CVE-2023-28782'"