CVE-2026-66146 in GMS
Summary
by MITRE • 08/11/2026
Multiple Cross-Site Scripting (XSS) vulnerabilities were identified in GMS 9.5.1 (Build 9510.1044) and earlier versions that allow a remote attacker to execute javascript script in a user's browser.
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Analysis
by VulDB Data Team • 08/11/2026
Multiple cross-site scripting vulnerabilities in GMS 9.5.1 and earlier versions represent a critical security flaw that enables remote attackers to inject malicious javascript code into user browsers through improperly sanitized input fields. These vulnerabilities fall under CWE-79 which specifically addresses cross-site scripting attacks where web applications fail to properly validate or escape user-supplied data before rendering it in web pages. The affected system processes user input without adequate sanitization mechanisms, creating an attack surface where malicious actors can craft payloads that execute arbitrary javascript code within the context of a victim's browser session.
The technical implementation of these vulnerabilities stems from insufficient input validation and output encoding practices within the GMS application framework. Attackers can exploit these weaknesses by submitting crafted malicious data through various input vectors including form fields, URL parameters, or API endpoints that do not properly filter or escape special characters. When the application subsequently renders this unvalidated data without proper context-aware escaping, the injected javascript executes in the victim's browser with the privileges of the authenticated user. This creates a persistent threat where attackers can steal session cookies, perform unauthorized actions on behalf of users, or redirect victims to malicious sites.
The operational impact of these vulnerabilities extends beyond simple script execution to encompass comprehensive session hijacking and privilege escalation capabilities. According to ATT&CK framework techniques T1539 and T1078, successful exploitation allows attackers to maintain persistent access through stolen credentials and establish footholds within the target environment. The remote nature of these attacks means that threat actors can compromise users from anywhere in the world without requiring physical access to the system infrastructure. Additionally, since these vulnerabilities affect the core application functionality, they can potentially impact multiple users simultaneously, amplifying the scope of potential damage.
Mitigation strategies should focus on implementing comprehensive input validation and output encoding controls throughout the application stack. Organizations must deploy proper Content Security Policy headers to limit script execution sources and implement strict input sanitization routines that filter or escape dangerous characters before any data processing occurs. The principle of least privilege should be enforced through proper session management practices, including secure cookie attributes and regular session token rotation. Security patches and updates should be applied immediately upon availability, with network segmentation and monitoring solutions deployed to detect anomalous traffic patterns indicative of exploitation attempts. Regular security testing including automated scanning and manual penetration testing should be conducted to identify similar vulnerabilities in related components and prevent future incidents that align with ATT&CK techniques targeting web application security weaknesses.