CVE-2017-18583 in post-pay-counter Plugin
Summary
by MITRE
The post-pay-counter plugin before 2.731 for WordPress has PHP Object Injection.
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Analysis
by VulDB Data Team • 12/01/2023
The post-pay-counter plugin for WordPress contains a critical PHP Object Injection vulnerability that affects versions prior to 2.731. This vulnerability resides within the plugin's handling of user-supplied data, specifically in how it processes serialized PHP objects through the wp_ajax_nopriv_ hook. The flaw allows attackers to inject malicious PHP objects into the application's execution flow through unvalidated input parameters, potentially enabling arbitrary code execution on the target WordPress site. The vulnerability is particularly dangerous because it operates within the WordPress admin-ajax.php endpoint, which is commonly used for handling asynchronous requests and is often accessible without authentication. This makes the attack surface significantly broader than typical plugin vulnerabilities that require administrative privileges.
The technical implementation of this vulnerability stems from the plugin's failure to properly validate and sanitize input data before deserializing PHP objects. When a user submits data through the affected endpoint, the plugin directly passes this data to PHP's unserialize() function without adequate security checks. According to CWE-502, this represents a direct violation of secure coding practices for deserialization operations, where untrusted data is processed without proper sanitization. The vulnerability allows an attacker to craft malicious serialized objects that, when deserialized, execute arbitrary PHP code on the server. This type of injection is particularly effective because it leverages the inherent capabilities of PHP's object serialization system, which can trigger magic methods like __wakeup() or __destruct() during the deserialization process, providing multiple attack vectors for code execution.
The operational impact of this vulnerability extends beyond simple code execution, as it enables attackers to perform a wide range of malicious activities including data exfiltration, privilege escalation, and persistent backdoor installation. An attacker who successfully exploits this vulnerability can gain full control over the compromised WordPress installation, potentially leading to complete server compromise and further lateral movement within the network. The attack can be executed through simple HTTP requests that include malicious serialized data in the POST parameters, making it relatively easy to exploit. According to ATT&CK framework's T1505.003 technique, this vulnerability aligns with the exploitation of web application vulnerabilities for code injection, while also supporting T1078.004 for account manipulation through compromised credentials that may be obtained through the exploitation. The vulnerability affects all WordPress installations running the affected plugin version, regardless of the underlying server configuration or security measures in place, making it particularly dangerous for widespread deployment.
Mitigation strategies for this vulnerability require immediate action including updating the post-pay-counter plugin to version 2.731 or later, which includes proper input validation and sanitization measures. Organizations should also implement network-level protections such as web application firewalls that can detect and block malicious serialized object patterns in HTTP requests. Additionally, the principle of least privilege should be enforced by limiting access to the wp-admin-ajax.php endpoint and monitoring for unusual patterns in AJAX requests. Security monitoring should include detection of suspicious serialized data patterns in application logs, while regular security audits should verify that no other plugins or themes contain similar deserialization vulnerabilities. The vulnerability also highlights the importance of input validation at multiple levels, as proper sanitization of user inputs before any deserialization operations can prevent exploitation. Organizations should also consider implementing automated patch management systems to ensure timely updates of all WordPress plugins and themes, as this vulnerability demonstrates the critical need for maintaining current security versions.