TypiCMS Core, a multilingual content management system built on Laravel, suffers from a stored cross-site scripting (XSS) vulnerability identified as CVE-2026-27621. This vulnerability affects versions prior to 16.1.7 and resides in the file upload module, specifically in handling SVG files. While the system performs MIME type validation to ensure only SVG files are uploaded, it fails to sanitize the SVG content itself. SVG files can embed JavaScript, and an attacker can craft an SVG payload containing malicious scripts. When a user with permission to view or manage uploaded files, such as an administrator, accesses the malicious SVG through the application, the embedded JavaScript executes in their browser context. This can lead to session hijacking or other client-side attacks. Additionally, a bug in the SVG parsing logic causes a 500 internal server error if the SVG lacks a viewBox attribute; however, this does not mitigate the vulnerability since attackers can include a valid viewBox attribute in their payload. The vulnerability requires the attacker to have file upload permissions and some user interaction (viewing the file) to trigger the exploit. The CVSS 4.0 vector indicates network attack vector, low attack complexity, no privileges required beyond file upload permissions, user interaction required, and high impact on confidentiality. The vulnerability was publicly disclosed on February 25, 2026, and fixed in TypiCMS Core version 16.1.7. No known exploits have been reported in the wild to date.

This vulnerability poses a significant risk to organizations using TypiCMS Core versions prior to 16.1.7, especially those allowing multiple users to upload files and administrators or privileged users to view uploaded content. Successful exploitation can lead to session hijacking, unauthorized actions performed under the victim's credentials, and potential compromise of sensitive administrative functions. Since the attack vector is stored XSS, the malicious payload persists and can affect multiple users over time. This can undermine the integrity and confidentiality of the CMS environment, potentially leading to data breaches or unauthorized content manipulation. The vulnerability could also be leveraged as a foothold for further attacks within the organization's network. Although exploitation requires file upload permissions and user interaction, these conditions are common in CMS environments, increasing the practical risk. The 500 error bug does not mitigate the threat, as attackers can bypass it easily. Organizations relying on TypiCMS for content management, especially those with public-facing administrative interfaces, are at risk of reputational damage, data loss, and operational disruption if this vulnerability is exploited.

Organizations should immediately upgrade TypiCMS Core to version 16.1.7 or later, where this vulnerability is patched. Until the upgrade is applied, administrators should restrict file upload permissions to trusted users only and monitor uploaded SVG files for suspicious content. Implementing additional server-side SVG sanitization tools that remove scripts and potentially dangerous elements can reduce risk. Web application firewalls (WAFs) with rules targeting SVG-based XSS payloads may provide temporary protection. Educate users, especially administrators, to be cautious when opening uploaded SVG files and consider disabling SVG uploads if not strictly necessary. Regularly audit file upload modules and logs for unusual activity. Employ Content Security Policy (CSP) headers to limit script execution contexts and reduce the impact of XSS attacks. Finally, conduct penetration testing focused on file upload functionalities to detect similar vulnerabilities proactively.