CVE-2026-4316 in IsMyGym
Summary
by MITRE • 10/26/2026
Reflected Cross-Site Scripting (XSS) in Gym Management Software IsMyGym by Zuinq Studio affecting the reservation endpoint where the 'ret' parameter is reflected in the HTTP response without any proper sanitization. Successfull explotation of this vulnerability could allow an attacker to inject arbitrary JavaScript code executed in the context of the victim’s browser.
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Analysis
by VulDB Data Team • 10/26/2026
The identified vulnerability represents a classic instance of Reflected Cross-Site Scripting within the IsMyGym application developed by Zuinq Studio, specifically targeting the reservation management endpoint. This security flaw arises from inadequate input validation and output encoding mechanisms when processing user-supplied data via the 'ret' parameter. In this architectural pattern, malicious script payloads are embedded directly into HTTP requests, typically through URL manipulation or form submissions, and subsequently reflected back in the server's response without being sanitized or encoded by the application logic. This lack of sanitization allows the browser to interpret the injected content as executable code rather than plain text data, fundamentally breaking the isolation between user input and application output that is critical for web security.
From a technical perspective, the exploitation vector relies on the victim interacting with a specially crafted URL or form submission where the 'ret' parameter contains malicious JavaScript. When the server processes this request, it fails to escape special characters such as angle brackets, quotes, or ampersands before including the input in the HTML response body. Consequently, when the victim's browser renders the page, it executes the injected script within the security context of the IsMyGym domain. This environment is particularly dangerous because scripts executed in this context possess full access to cookies, session tokens, local storage, and other sensitive data associated with the user’s active session on the platform. The vulnerability aligns closely with CWE-79, which categorizes improper neutralization of input during web page generation as a primary weakness leading to cross-site scripting attacks.
The operational impact of successfully exploiting this reflected XSS vulnerability is severe, primarily facilitating account takeover and unauthorized access to sensitive gym management data. An attacker can leverage the executed script to steal session cookies or authentication tokens, effectively impersonating legitimate users without needing their passwords. Beyond credential theft, the attack vector enables phishing campaigns where attackers can inject deceptive login forms that harvest credentials from unsuspecting victims. Furthermore, if the application handles administrative functions for gyms and members, an attacker could manipulate reservation data, delete records, or alter membership statuses by executing commands on behalf of authenticated administrators. This compromise undermines the integrity and confidentiality of the entire system, potentially leading to significant financial loss and reputational damage for both the software provider and its clients.
In terms of threat modeling, this vulnerability maps directly to MITRE ATT&CK technique T1059.007, which covers JavaScript-based command execution within a browser environment. The attack lifecycle typically involves reconnaissance to identify vulnerable endpoints, weaponization by crafting malicious payloads often hosted on external servers or embedded in URLs via URL encoding techniques like XSSER, and delivery through social engineering tactics such as phishing emails containing links to the compromised reservation page. Once delivered, the exploitation phase triggers the execution of the payload, followed by actions on objectives such as credential harvesting or data exfiltration. The reflected nature of this XSS means that each attack requires individualized targeting via a unique link, making large-scale automated scanning less effective but increasing the success rate against targeted individuals who trust the source of the link.
To mitigate this vulnerability and prevent future occurrences, developers must implement strict input validation and output encoding strategies across all endpoints handling user data. Specifically, the 'ret' parameter should be validated to ensure it contains only expected character sets such as alphanumeric characters or specific allowed symbols, rejecting any input containing HTML tags or JavaScript event handlers. More importantly, when rendering this data in HTTP responses, developers must apply context-aware output encoding appropriate for the location within the HTML document, ensuring that special characters are converted into their corresponding HTML entities before being sent to the client browser. Implementing a Content Security Policy (CSP) header can also serve as an effective defense-in-depth measure by restricting the sources from which scripts can be loaded and executed, thereby neutralizing many XSS payloads even if they bypass input filters. Regular security testing using both static application security testing tools and dynamic analysis during development cycles is essential to identify such flaws before deployment in production environments.