CVE-2026-56736 in PhpMyfaq
Summary
by MITRE • 09/24/2026
phpMyFAQ is an open source FAQ web application. A stored cross-site scripting (XSS) vulnerability in versions prior to 4.2.0-alpha allows any unauthenticated user (or low-privileged registered user) to inject arbitrary JavaScript that executes in an administrator's browser when they review or edit a user-submitted FAQ entry. This leads to admin account takeover via session theft. The vulnerability exists because `html_entity_decode()` converts HTML entities into executable HTML after `strip_tags()` has already passed them through, and the admin template renders the content with Twig's `|raw` filter without any output sanitization. Version 4.2.0-alpha fixes the issue.
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Analysis
by VulDB Data Team • 09/24/2026
phpMyFAQ is a widely deployed open-source FAQ web application that facilitates knowledge management by allowing users to submit questions and answers for public or internal consumption. In versions prior to 4.2.0-alpha, the application contains a critical stored cross-site scripting vulnerability within its content submission and administration workflows. This flaw permits unauthenticated attackers or low-privileged registered users to inject malicious JavaScript payloads into FAQ entries. Because the data is stored in the database without proper sanitization at the point of entry, these scripts persist on the server side until they are retrieved by an administrator for review or editing purposes.
The technical root cause of this vulnerability lies in a flawed sequence of input validation and output encoding functions within the application's backend logic. Specifically, the code utilizes `strip_tags()` to remove HTML tags from user-supplied data, followed immediately by `html_entity_decode()`. This ordering is problematic because `html_entity_decode()` converts encoded characters back into their literal representations, effectively reversing any sanitization that might have been intended or allowing attackers to bypass tag stripping if they use alternative encoding techniques. Consequently, malicious scripts survive the validation process and are stored in the database as part of the FAQ entry content.
The exploitation vector is triggered when an administrator accesses the administrative interface to review or edit a user-submitted FAQ entry. The application's admin template renders this stored content using Twig with the `|raw` filter. This directive instructs the templating engine to output the data without any additional escaping, meaning that if the payload contains executable JavaScript, it will be interpreted and executed by the administrator's web browser in the context of the phpMyFAQ session. This behavior transforms a simple text storage issue into a severe security breach where client-side code runs with the privileges of the logged-in admin user.
The operational impact of this vulnerability is significant, primarily leading to complete administrative account takeover through session theft or manipulation. An attacker can craft a payload that exfiltrates the administrator's session cookies to an external server controlled by the attacker. With access to these valid session tokens, the attacker can impersonate the administrator without needing credentials. This allows for unauthorized modification of site settings, deletion of data, injection of further malicious content, or full compromise of the underlying system if administrative functions allow file uploads or configuration changes. The attack is particularly dangerous because it does not require direct interaction with the victim beyond luring them to a specific page within the admin panel, often via social engineering or by embedding links in other public-facing parts of the site.
From a classification perspective, this vulnerability aligns with CWE-79: Improper Neutralization of Input During Web Page Generation, commonly known as Cross-Site Scripting (XSS). More specifically, it is categorized under CWE-836: Use of Password Hash With Insufficient Computational Effort if session fixation or theft leads to authentication bypass, but primarily falls under the stored XSS category where malicious scripts are persistently stored. In terms of offensive security frameworks, this attack maps directly to MITRE ATT&CK technique T1059.007: Command and Scripting Interpreter: JavaScript, utilized for initial access via phishing or drive-by techniques when combined with social engineering, and potentially T1534: Internal Spearphishing if the attacker uses internal communication channels to lure admins.
To mitigate this vulnerability, organizations running phpMyFAQ versions prior to 4.2.0-alpha must upgrade immediately to version 4.2.0-alpha or later, where the developers have corrected the input validation and output encoding logic. Until an upgrade is feasible, administrators should implement strict access controls on the admin interface using multi-factor authentication to reduce the risk of session theft exploitation. Additionally, deploying a Web Application Firewall with rules capable of detecting and blocking stored XSS payloads in form submissions can provide a temporary layer of defense. It is also critical to ensure that all administrative interfaces are protected by strong network-level security policies and monitored for unusual activity indicative of session hijacking attempts.