CVE-2026-1466 is a cross-site scripting vulnerability identified in the Jirafeau project, a web-based file sharing application. The vulnerability stems from the application's mechanism to prevent browser preview of potentially dangerous file types such as SVG and HTML, which can contain executable JavaScript. Jirafeau attempts to restrict previews to files with MIME types starting with image (excluding image/svg+xml), video, or audio. However, an attacker can craft an HTTP request with an invalid MIME type, for example, 'image.', which bypasses the MIME type check. When the browser attempts to preview the file, it performs MIME sniffing to detect the actual content type, potentially recognizing it as SVG or HTML and executing embedded JavaScript code. This leads to an XSS attack vector where malicious scripts run in the context of the victim's browser session. To mitigate this, the application should disable MIME sniffing by sending the HTTP header 'X-Content-Type-Options: nosniff', instructing browsers not to override the declared content type. The vulnerability has a CVSS 3.1 score of 6.1 (medium severity), with an attack vector of network, low attack complexity, no privileges required, but requiring user interaction to trigger. The impact affects confidentiality and integrity but not availability. There are no known exploits in the wild, and no patches are currently linked, indicating the need for proactive mitigation by administrators.

For European organizations, this vulnerability poses a risk primarily to confidentiality and integrity of user sessions and data accessed via Jirafeau instances. Attackers could execute malicious scripts in users' browsers, potentially stealing session tokens, cookies, or performing actions on behalf of the user. This could lead to unauthorized data access or manipulation within the file sharing environment. Since Jirafeau is used for sharing files, exploitation could also facilitate the delivery of further malware or phishing attempts. The impact is heightened in sectors where sensitive or regulated data is shared, such as finance, healthcare, or government agencies. The requirement for user interaction (previewing a file) limits the scope but does not eliminate risk, especially in environments with frequent file sharing. Additionally, the cross-site scripting could be leveraged in targeted attacks against European organizations using Jirafeau, especially if combined with social engineering. The lack of known exploits suggests a window for mitigation before widespread abuse occurs.

European organizations should immediately verify that their Jirafeau deployments send the HTTP header 'X-Content-Type-Options: nosniff' to prevent browsers from MIME sniffing and executing malicious scripts. Administrators should audit and enforce strict MIME type validation on uploaded files, rejecting or sanitizing files with ambiguous or invalid MIME types. Implementing Content Security Policy (CSP) headers can further reduce the risk by restricting script execution contexts. User education to avoid previewing suspicious files can reduce exploitation likelihood. Monitoring web server logs for unusual MIME types or preview requests can help detect attempted exploitation. If possible, upgrade to a Jirafeau version that addresses this vulnerability once available. Network-level controls such as web application firewalls (WAFs) can be configured to detect and block malformed MIME type requests. Finally, organizations should review their file sharing policies to limit exposure and ensure secure handling of file previews.