CVE-2026-1466 is a cross-site scripting vulnerability classified under CWE-79 affecting the Jirafeau project, an open-source file sharing platform. Jirafeau attempts to prevent browser previews of potentially dangerous text files by restricting previews to certain MIME types, specifically those starting with 'image' (excluding 'image/svg+xml'), video, and audio. However, the vulnerability arises because an attacker can craft HTTP requests with manipulated or invalid MIME types such as 'image.' (note the trailing dot), which bypass the MIME type validation. When the browser attempts to preview such files, it performs MIME sniffing to determine the actual content type. This sniffing can lead to the browser detecting the file as SVG, which may contain embedded JavaScript, thus enabling execution of malicious scripts in the victim's browser context. This can lead to theft of sensitive information, session hijacking, or other malicious actions compromising confidentiality and integrity. The vulnerability does not affect availability and does not require authentication, but user interaction is necessary to trigger the preview and exploit the vulnerability. The recommended mitigation is to disable MIME sniffing by setting the HTTP header 'X-Content-Type-Options: nosniff' and to improve MIME type validation to reject malformed or suspicious MIME types. Currently, no public exploits are known in the wild, and no patches are linked yet. The CVSS v3.1 score is 6.1 (medium severity) reflecting the network attack vector, low complexity, no privileges required, user interaction required, and partial impact on confidentiality and integrity.

For European organizations, this vulnerability poses a moderate risk primarily to confidentiality and integrity of data accessed through Jirafeau instances. Attackers could exploit this flaw to execute malicious scripts in users' browsers, potentially leading to session hijacking, credential theft, or unauthorized actions performed on behalf of the user. Since Jirafeau is used for file sharing, sensitive corporate or personal data could be exposed or manipulated. The vulnerability requires user interaction, so phishing or social engineering could be used to lure victims into previewing malicious files. The impact is heightened in sectors relying on secure file sharing, such as finance, healthcare, and government. Given the cross-site scripting nature, the vulnerability could also facilitate further attacks like drive-by downloads or spreading malware. However, the lack of known exploits and the medium severity score suggest the threat is moderate but should not be ignored. Organizations using Jirafeau or similar platforms should assess exposure and prioritize mitigation to prevent potential data breaches or reputational damage.

Organizations should immediately verify if they are running vulnerable versions of Jirafeau and apply any available patches once released. In the absence of patches, administrators should configure their web servers or reverse proxies to include the HTTP header 'X-Content-Type-Options: nosniff' to disable MIME sniffing, preventing browsers from interpreting files as executable scripts based on content. Additionally, enhance MIME type validation logic to reject malformed or suspicious MIME types such as those ending with a dot or containing invalid characters. User education is critical to reduce the risk of social engineering attacks that could trick users into previewing malicious files. Monitoring and logging preview requests can help detect suspicious activity. Where possible, restrict file preview functionality to trusted users or disable it entirely if not required. Employ Content Security Policy (CSP) headers to limit script execution contexts and reduce the impact of potential XSS attacks. Regular security assessments and penetration testing focusing on file upload and preview features will help identify similar weaknesses.