CVE-2026-25739 in Indico
Summary
by MITRE • 02/19/2026
Indico is an event management system that uses Flask-Multipass, a multi-backend authentication system for Flask. Versions prior to 3.3.10 are vulnerable to cross-site scripting when uploading certain file types as materials. Users should upgrade to version 3.3.10 to receive a patch. To apply the fix itself updating is sufficient, but to benefit from the strict Content Security Policy (CSP) Indico now applies by default for file downloads, update the webserver config in case one uses nginx with Indico's `STATIC_FILE_METHOD` set to `xaccelredirect`. For further directions, consult the GitHub Security advisory or Indico setup documentation. Some workarounds are available. Use the webserver config to apply a strict CSP for material download endpoints, and/or only let trustworthy users create content (including material uploads, which speakers can typically do as well) on Indico.
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Analysis
by VulDB Data Team • 02/19/2026
CVE-2026-25739 represents a cross-site scripting vulnerability affecting Indico event management systems prior to version 3.3.10, specifically within the Flask-Multipass authentication framework. This vulnerability stems from insufficient input validation during file upload processing, particularly when handling certain file types designated as materials within the system. The flaw allows malicious actors to inject malicious scripts into file metadata or content that gets rendered in user browsers, creating potential attack vectors for session hijacking, data exfiltration, or arbitrary code execution. The vulnerability aligns with CWE-79, which categorizes cross-site scripting flaws as weaknesses in input validation and output encoding. The issue manifests when users upload materials through the web interface, with the malicious scripts executing in the context of other users who view or interact with these materials.
The technical implementation of this vulnerability exploits the lack of proper sanitization in the file handling pipeline, particularly when processing file metadata or content that gets embedded in web responses. When Indico processes uploaded materials, it fails to adequately escape or validate user-supplied content before rendering it in web contexts, creating opportunities for attackers to inject malicious JavaScript code. This vulnerability specifically impacts the material upload functionality and affects users who have permissions to add or modify content, including speakers who can typically upload materials. The flaw does not require authentication to exploit, making it particularly dangerous as it can be leveraged by any user with access to the upload functionality. Attackers can craft malicious files that, when uploaded and subsequently accessed by other users, execute scripts in their browsers, potentially stealing session cookies or redirecting them to malicious sites.
The operational impact of this vulnerability extends beyond simple script execution, as it can enable attackers to establish persistent access to the system through session manipulation and data theft. When combined with other attack vectors, this XSS flaw could allow adversaries to escalate privileges, access sensitive event information, or compromise the entire Indico deployment. The vulnerability affects organizations using Indico for conference management, academic events, and other collaborative environments where users upload materials. Organizations relying on Indico for hosting events with multiple participants face significant risk as attackers can exploit this vulnerability to target any user who accesses the compromised materials. The attack surface is particularly broad given that speakers and organizers typically possess upload privileges, making the system vulnerable to insider threats as well as external attackers who gain access through other means.
The recommended mitigation strategy involves upgrading to Indico version 3.3.10, which includes proper input sanitization and output encoding mechanisms to prevent script injection. Additionally, system administrators must configure their web servers to implement strict Content Security Policies for file download endpoints, particularly when using nginx with Indico's STATIC_FILE_METHOD set to xaccelredirect. This enhancement provides an additional layer of protection by restricting the sources from which scripts can be loaded, effectively mitigating the XSS attack vector. The fix addresses the root cause by implementing proper HTML escaping of user-supplied content and by enforcing stricter validation of uploaded file metadata. Organizations should also consider implementing user access controls to limit content creation privileges, ensuring only trusted users can upload materials, and should monitor for suspicious upload activity. The vulnerability's remediation aligns with ATT&CK technique T1059.007 for script injection and T1566 for social engineering, emphasizing the importance of defensive measures against both automated and targeted attacks. System administrators should consult the GitHub Security advisory and Indico setup documentation for specific configuration guidance, particularly regarding CSP implementation and web server adjustments.