Medium · published October 4, 2025
KUNO CMS is a fully deployable full-stack blog application. Versions 1.3.13 and below contain validation flaws in its file upload functionality that can be exploited for stored XSS. The upload endpoint only validates file types based on Content-Type headers, lacks file content analysis and extension whitelist restrictions, allowing attackers to upload SVG files containing malicious scripts (disguised as images). When users access the uploaded resource pages, arbitrary JavaScript executes in their browsers. This issue is fixed in version 1.3.14.