CVE-2024-56291: PlainInventory Object Injection Flaw

CVE-2024-56291 Overview

CVE-2024-56291 is a PHP Object Injection vulnerability affecting the plainware PlainInventory z-inventory-manager WordPress plugin. The flaw stems from deserialization of untrusted data [CWE-502] in plugin versions up to and including 3.1.6. Unauthenticated attackers can supply crafted serialized payloads to trigger object instantiation within the application context. When combined with a suitable property-oriented programming (POP) chain, exploitation can lead to remote code execution, data tampering, or full site compromise.

Critical Impact

Network-reachable attackers can inject malicious PHP objects without authentication, potentially compromising confidentiality, integrity, and availability of affected WordPress sites.

Affected Products

• plainware PlainInventory z-inventory-manager WordPress plugin
• All versions from n/a through <= 3.1.6
• WordPress installations using the inventory management plugin

Discovery Timeline

• 2025-01-07 - CVE-2024-56291 published to NVD
• 2026-04-23 - Last updated in NVD database

Technical Details for CVE-2024-56291

Vulnerability Analysis

The vulnerability resides in the z-inventory-manager plugin's handling of serialized PHP data. The plugin passes attacker-controlled input to a deserialization routine without validating its origin or structure. PHP's unserialize() function reconstructs arbitrary object graphs from input strings, invoking magic methods such as __wakeup(), __destruct(), or __toString() as objects are created and destroyed.

When the plugin or its dependent libraries contain classes with exploitable magic methods, an attacker can chain them into a POP gadget. This chain can read files, write to disk, execute system commands, or invoke arbitrary methods. The EPSS score of 0.872% (75.55th percentile) reflects measurable exploitation interest for object injection flaws of this class.

Root Cause

The root cause is unsafe use of PHP deserialization on data sourced from HTTP request parameters, cookies, or stored values that an attacker can influence. The plugin fails to apply allow-list class restrictions through the allowed_classes option or to migrate to safer formats such as JSON. See the Patchstack Vulnerability Report for advisory details.

Attack Vector

An unauthenticated remote attacker sends a crafted HTTP request containing a malicious serialized PHP payload to a vulnerable plugin endpoint. The plugin deserializes the payload, instantiating attacker-defined object structures. If a usable gadget chain exists in WordPress core, the plugin, or other installed plugins, the chain triggers code execution or file system operations under the web server's privileges.

The vulnerability mechanism follows the classic PHP object injection pattern. See the security advisory referenced above for technical specifics on the affected code paths.

Detection Methods for CVE-2024-56291

Indicators of Compromise

• HTTP requests to z-inventory-manager endpoints containing serialized PHP strings such as O:, a:, or s: patterns in parameters or cookies
• Unexpected PHP files created in the WordPress wp-content/uploads/ or plugin directories following inbound traffic
• Web server processes spawning shell utilities (sh, bash, wget, curl) without legitimate administrative context
• Modifications to WordPress core files, wp-config.php, or installation of unknown administrative users

Detection Strategies

• Inspect web server access logs for POST and GET requests to plugin handlers containing URL-encoded unserialize payload markers
• Monitor PHP error logs for warnings related to __wakeup, __destruct, or class instantiation failures during request processing
• Apply WordPress security scanners that flag z-inventory-manager versions <= 3.1.6 as vulnerable

Monitoring Recommendations

• Forward web server, PHP-FPM, and WordPress audit logs to a centralized SIEM for correlation against object injection signatures
• Track outbound network connections from PHP worker processes to detect reverse shells or staging traffic
• Alert on file integrity changes within plugin, theme, and core directories using a host-based monitoring solution

How to Mitigate CVE-2024-56291

Immediate Actions Required

• Update the z-inventory-manager plugin to a version above 3.1.6 once the vendor publishes a fix
• Disable or remove the plugin if a patched version is not yet available and the functionality is non-critical
• Restrict access to WordPress admin and plugin endpoints using a web application firewall ruleset that blocks serialized PHP payloads
• Audit the WordPress installation for indicators of compromise listed above and rotate administrator credentials if signs of intrusion exist

Patch Information

No fixed version was specified in the advisory at publication time. Monitor the Patchstack Vulnerability Report and the official plugin repository for vendor updates beyond version 3.1.6.

Workarounds

• Deploy WAF rules that inspect request bodies and query strings for serialized PHP object markers (O:\d+:")
• Restrict plugin endpoint access to authenticated administrative IP addresses via web server access control
• Apply the principle of least privilege to the PHP process user to limit the impact of successful exploitation

# Example ModSecurity rule to block serialized PHP object payloads
SecRule ARGS|REQUEST_BODY|REQUEST_COOKIES "@rx O:[0-9]+:\"[a-zA-Z_]+\":[0-9]+:" \
    "id:1056291,phase:2,deny,status:403,log,\
    msg:'PHP Object Injection attempt - CVE-2024-56291'"