CVE-2026-112867 in H5P Plugin
Summary
by MITRE • 10/22/2026
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability in H5P H5P h5p allows Stored XSS.This issue affects H5P: from n/a through 1.17.9.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 10/22/2026
The identified vulnerability represents a classic instance of Improper Neutralization of Input During Web Page Generation, commonly known as Cross-site Scripting or XSS. Specifically, this is classified under CWE-80 and manifests as a Stored XSS flaw within the H5P content management framework. Unlike reflected XSS attacks where malicious scripts are executed via manipulated URLs in real-time, stored vulnerabilities involve the persistence of malicious input on the target server. In the context of H5P, which serves interactive educational content such as quizzes, presentations, and multimedia interactions, this flaw allows an attacker to inject executable JavaScript code that is subsequently saved within the platform's database or file storage systems. This means the payload does not need to be manually triggered by a victim through a link; instead, it remains dormant until another user accesses the compromised H5P content, at which point the browser automatically executes the injected script in the context of the vulnerable application.
The technical root cause lies in insufficient validation and sanitization mechanisms when processing input data that is destined for rendering within web pages. When users or administrators create or edit H5P packages, the system fails to adequately strip out or encode potentially dangerous characters such as angle brackets, quotes, and ampersands before storing them. Consequently, when this content is retrieved and displayed in a user's browser, the malicious script becomes part of the Document Object Model (DOM). Because modern browsers execute scripts embedded within HTML structures by default unless strict Content Security Policies are enforced, the injected code runs with the same privileges as legitimate application scripts. This typically includes access to session cookies, local storage tokens, and other sensitive authentication credentials associated with the user's current session on the H5P platform.
The operational impact of this vulnerability is severe due to its persistent nature and broad potential reach within educational or corporate training environments where H5P is frequently deployed. An attacker who successfully exploits this flaw can achieve full account compromise for any user viewing the affected content, including administrators with elevated privileges if they view the malicious package. This leads directly to data exfiltration, session hijacking, and potentially further lateral movement within the network infrastructure hosting the platform. From a threat intelligence perspective, this aligns with MITRE ATT&CK technique T1059.007 (JavaScript), which describes how attackers use JavaScript for execution during initial access or persistence phases. The ability to store malicious payloads means that even after the initial exploit is discovered and patched, previously infected content may continue to compromise users until it is manually removed or sanitized from the database, creating a long-tail risk profile for organizations relying on this software.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. The primary defense involves upgrading H5P to version 1.18.0 or later, where developers have implemented stricter input validation and output encoding routines to neutralize special characters before they are rendered in the browser context. For organizations unable to upgrade immediately due to compatibility constraints with existing content packages, implementing a Web Application Firewall (WAF) can provide temporary protection by filtering out known XSS payloads at the network perimeter. Additionally, enforcing strict Content Security Policy headers that restrict script execution sources and disable inline scripts can significantly reduce the impact of any successful injection attempts. Regular security audits focusing on input handling in user-generated content modules are also recommended to ensure that future updates or custom integrations do not reintroduce similar weaknesses into the application lifecycle.