CVE-2026-78175 in Tutor LMS
Summary
by MITRE • 09/12/2026
The Tutor LMS – eLearning and online course solution plugin for WordPress is vulnerable to PHP Object Injection in all versions up to, and including, 4.0.7 via the `withdraw_method_field` parameter of the `tutor_save_withdraw_account` AJAX handler. This is due to the handler lacking any capability or role check, relying solely on a nonce, while also passing attacker-supplied values through `esc_sql()`, which replaces every `%` character with a 66-byte HMAC placeholder token before the data is serialized and stored via `update_user_meta()`; when the meta is later retrieved, the placeholder is collapsed back to a single `%`, leaving serialized string length declarations 65 bytes greater than the actual content, and because array keys originate from entirely unescaped POST field names, `unserialize()` over-reads into attacker-controlled bytes, allowing injection of an arbitrary serialized object stream. This makes it possible for authenticated attackers, with subscriber-level access and above, to achieve remote code execution on the server by triggering the `GuzzleHttp\Cookie\FileCookieJar` POP chain, reachable via the `spl_autoload_register` loader in `TUTOR\RestAPI` which loads the plugin's own bundled PayPal Composer autoloader, writing attacker-controlled content to an attacker-specified filename. This has an unauthenticated pathway when user registration is enabled, which is common for students and teachers to register, and it requires the monetization feature to be enabled.
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Analysis
by VulDB Data Team • 09/12/2026
The Tutor LMS plugin for WordPress contains a critical PHP Object Injection vulnerability affecting all versions up to 4.0.7. This flaw resides within the `tutor_save_withdraw_account` AJAX handler, which processes the `withdraw_method_field` parameter without implementing any capability or role verification checks. The security model relies exclusively on nonce validation, which is insufficient against authenticated attackers who possess subscriber-level access or higher privileges. The core technical failure stems from improper data handling during serialization and storage operations. Specifically, the input values are passed through `esc_sql()`, a function designed for SQL escaping rather than general string sanitization in this context. This process replaces every percent sign with a 66-byte HMAC placeholder token before the data is serialized and stored via `update_user_meta`.
When the compromised metadata is later retrieved from the database, the system collapses these long placeholders back into single percent characters. This transformation results in serialized strings where length declarations are exactly sixty-five bytes greater than the actual content size. Because array keys originate directly from unescaped POST field names, this discrepancy causes `unserialize()` to over-read beyond the intended data boundaries. The parser continues reading into adjacent memory or subsequent attacker-controlled bytes within the request payload, allowing for the injection of an arbitrary serialized object stream. This mechanism effectively bypasses standard serialization safeguards and enables attackers to craft malicious payloads that exploit PHP's magic methods during deserialization.
The operational impact is severe, as this vulnerability allows authenticated users with minimal privileges to achieve remote code execution on the target server. Attackers can leverage a specific Proof of Concept chain involving `GuzzleHttp\Cookie\FileCookieJar`. This class serves as an entry point for exploitation because it interacts with file systems in ways that can be manipulated through deserialization side effects. The exploit is facilitated by the presence of `spl_autoload_register` within the `TUTOR\RestAPI` namespace, which loads a bundled PayPal Composer autoloader. By controlling the serialized object graph, an attacker can force the application to write malicious content to a file path specified entirely by the attacker. This capability effectively grants full control over server-side files, leading to complete system compromise.
An unauthenticated attack vector exists under specific configuration conditions where user registration is enabled, which is common for platforms allowing students and teachers to create accounts independently. In such scenarios, an external actor can register a new account with subscriber-level access and subsequently exploit the vulnerability without needing pre-existing credentials beyond those obtained through public registration. Additionally, successful exploitation requires that the monetization feature be enabled within the WordPress installation, as this activates the relevant withdrawal handlers and associated libraries containing the vulnerable code paths.
Mitigation strategies must address both immediate remediation and long-term security posture improvements. The primary defense is to upgrade the Tutor LMS plugin to a version later than 4.0.7 where these issues have been patched by the developers. Until an update is applied, administrators should consider disabling user registration if feasible or restricting access to the monetization features until patches are deployed. From a defensive engineering perspective, this vulnerability highlights the dangers of relying solely on nonces for authorization and using SQL escaping functions for general input sanitization in serialization contexts. Security architectures should enforce strict role-based access control checks before processing sensitive AJAX requests. Furthermore, developers must avoid passing user-controlled data directly into `unserialize()` without rigorous validation or use alternative data formats like JSON that do not support arbitrary object instantiation. Adhering to secure coding standards such as CWE-502 for deserialization of untrusted data and implementing input validation aligned with OWASP guidelines can prevent similar exploitation vectors in future development cycles.