CVE-2026-28083 in Flatsome Plugin
Summary
by MITRE • 02/26/2026
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability in UX-themes Flatsome flatsome allows Stored XSS.This issue affects Flatsome: from n/a through <= 3.20.1.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 02/26/2026
The vulnerability identified as CVE-2026-28083 represents a critical cross-site scripting flaw within the UX-themes Flatsome flatsome WordPress theme. This stored XSS vulnerability arises from inadequate input sanitization during web page generation processes, creating a persistent security risk that can compromise user sessions and execute malicious code in the context of affected websites. The vulnerability specifically impacts versions of the Flatsome theme ranging from the initial release through version 3.20.1, indicating a widespread exposure across multiple iterations of this popular e-commerce theme.
The technical flaw stems from the theme's failure to properly neutralize user-supplied input before incorporating it into dynamically generated web pages. When malicious actors exploit this weakness, they can inject malicious scripts into web pages that are subsequently stored on the server and executed whenever legitimate users access those pages. This stored nature of the vulnerability means that the malicious payload persists even after the initial injection, making it particularly dangerous as it can affect multiple users over extended periods. The vulnerability maps directly to CWE-79 - Improper Neutralization of Input During Web Page Generation, which classifies this as a classic XSS attack vector where user input is improperly handled during HTML generation.
The operational impact of this vulnerability extends beyond simple script execution, as it can enable attackers to perform session hijacking, steal sensitive user credentials, manipulate website content, and potentially escalate privileges within the affected WordPress environment. Given that Flatsome is a widely used theme for WooCommerce stores, the potential attack surface is substantial, with numerous e-commerce websites potentially at risk. The stored nature of the vulnerability means that even if users are aware of the threat, they may continue to be exposed as long as the malicious content remains in the system. This vulnerability aligns with ATT&CK technique T1531 - Account Access Removal and T1059.001 - Command and Scripting Interpreter, as it enables attackers to establish persistent access and execute malicious commands through compromised user sessions.
Mitigation strategies should prioritize immediate theme updates to versions that address this vulnerability, as provided by the vendor. Administrators should implement comprehensive input validation and output encoding mechanisms to prevent similar issues in custom code implementations. Additionally, implementing Content Security Policy headers can provide an additional layer of protection against XSS attacks, while regular security audits and penetration testing should be conducted to identify potential injection points. Network monitoring solutions should be configured to detect anomalous script execution patterns, and user education regarding suspicious website behavior remains crucial for early detection of exploitation attempts. The vulnerability underscores the importance of maintaining up-to-date third-party components and implementing robust security controls throughout the application development lifecycle to prevent such persistent threats from compromising user security.