CVE-2026-81338 in MasterStudy LMS Plugin
Summary
by MITRE • 09/23/2026
The MasterStudy LMS WordPress Plugin WordPress plugin before 3.7.50 does not properly sanitise and restrict HTML in user-submitted content before storing it and rendering it to other users, allowing users with subscriber-level accounts and above to perform stored HTML injection, such as embedding iframes, that can be leveraged for phishing and content spoofing against other users viewing the content.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 09/23/2026
The vulnerability identified in MasterStudy LMS WordPress Plugin versions prior to 3.7.50 represents a critical failure in input validation and output encoding mechanisms within the application's user-generated content handling processes. This flaw allows authenticated attackers with subscriber-level accounts or higher to inject malicious HTML code into stored data, which is subsequently rendered without proper sanitization when viewed by other users. The core technical deficiency lies in the plugin's inability to properly filter restrictive tags such as iframes before persisting them to the database and failing to encode these elements during rendering. This lack of strict content security policy enforcement creates a persistent vector for attack that does not require immediate user interaction beyond initial submission, distinguishing it from reflected variants by maintaining its malicious payload in the system's storage layer until accessed by victims.
From an operational perspective, this stored HTML injection vulnerability significantly expands the attack surface available to lower-privileged users within the WordPress ecosystem. By embedding iframes or other executable content structures, attackers can craft sophisticated phishing pages that mimic legitimate educational interfaces or external services trusted by the victim community. The impact extends beyond simple defacement; it enables credential harvesting, session hijacking through malicious scripts embedded in injected frames, and potential malware distribution depending on the specific payload constructed by the attacker. Since the vulnerability affects content visible to other users, a single compromised account can potentially expose multiple victims across different sessions without requiring further exploitation steps after the initial injection.
This flaw aligns with Common Weakness Enumeration CWE-79, which classifies improper neutralization of input during web page generation as Cross-site Scripting (XSS). Specifically, it falls under stored XSS where malicious scripts are permanently stored on target servers such as in a database or message board and subsequently executed when users request information from the server. In terms of adversary tactics, this vulnerability supports techniques categorized under ATT&CK ID T1059, specifically Command and Scripting Interpreter variants that leverage HTML-based execution contexts to perform unauthorized actions against end-users. The ability to inject iframes also relates to CWE-829 for inclusion of functionality from outside the boundary, allowing external domains to execute within the context of the trusted application domain.
Mitigation strategies must prioritize immediate version upgrades to 3.7.50 or later where these sanitization controls have been reinforced by the vendor. Administrators should also implement strict Content Security Policy headers that restrict frame sourcing and script execution from unauthorized origins, providing a defense-in-depth layer even if future vulnerabilities arise in similar plugins. Additionally, enforcing role-based access control to limit who can submit rich HTML content reduces the initial attack surface. Regular security audits focusing on input validation logic for all user-facing forms are essential to ensure that only expected data types and structures are accepted by the application backend.