CVE-2026-18391 in Subscriptions Plugin
Summary
by MITRE • 08/12/2026
The WooCommerce Subscriptions WordPress plugin before 9.1.0 does not validate user input before unserializing it on stores with High-Performance Order Storage enabled, leading to a PHP Object Injection issue which unauthenticated users can escalate to Remote Code Execution via a gadget chain present in the bundled dependencies.
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Analysis
by VulDB Data Team • 08/12/2026
The vulnerability exists within the WooCommerce Subscriptions plugin version 9.1.0 and earlier, specifically affecting WordPress installations that utilize High-Performance Order Storage functionality. This represents a critical security flaw that stems from insufficient input validation mechanisms during the unserialization process of user-supplied data. The issue manifests when the plugin processes serialized data without proper sanitization, creating an avenue for malicious actors to inject crafted objects into the application's memory space.
The technical exploitation occurs through PHP Object Injection techniques where unauthenticated attackers can manipulate serialized data payloads to trigger unintended object instantiation. When High-Performance Order Storage is enabled, the plugin's deserialization logic becomes particularly vulnerable because it processes user-controllable input without adequate validation checks. This vulnerability maps directly to CWE-502 which classifies unsafe deserialization as a critical weakness in software systems. The threat landscape is further exacerbated by the presence of gadget chains within the plugin's bundled dependencies, which allows attackers to chain multiple vulnerable methods together to achieve remote code execution capabilities.
The operational impact of this vulnerability is severe and far-reaching for WordPress administrators and store owners who have not updated to version 9.1.0 or later. Unauthenticated attackers can potentially gain complete control over affected systems, enabling them to execute arbitrary code, access sensitive data, modify store configurations, and ultimately compromise the entire e-commerce platform. The attack surface expands significantly because the vulnerability affects any store using High-Performance Order Storage, which is a common configuration among modern WooCommerce installations. This weakness can be leveraged for persistent backdoor establishment, data exfiltration, and further network infiltration activities that align with ATT&CK technique T1059.007 for command and scripting interpreter.
Mitigation strategies should prioritize immediate patching to version 9.1.0 or later where the input validation has been properly implemented. Administrators should also consider disabling High-Performance Order Storage temporarily if immediate patching is not feasible, though this may impact performance. Additional protective measures include implementing web application firewalls with rules targeting suspicious serialized data patterns, monitoring for unusual deserialization activities in server logs, and conducting thorough security audits of plugin dependencies. The remediation process must include comprehensive testing to ensure that the patched version functions correctly while maintaining all existing store functionalities. Organizations should also establish automated patch management processes to prevent similar vulnerabilities from arising in the future, as this incident highlights the importance of secure coding practices and regular dependency updates within WordPress ecosystems.