CVE-2026-107394 in Indico
Summary
by MITRE • 10/08/2026
Indico is an event management system that uses Flask-Multipass, a multi-backend authentication system for Flask. Prior to 3.3.13, the previous fix for CVE-2026-25738 did not cover an edge case, allowing an event organizer to submit a crafted URL that points to a prohibited local target but is accepted as valid by Indico. The organizer can read data returned by the target through affected Indico features. This issue is fixed in version 3.3.13.
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Analysis
by VulDB Data Team • 10/08/2026
Indico, a widely deployed open-source event management platform built on the Flask web framework, relies heavily on external authentication backends to manage user access and identity verification. The system utilizes Flask-Multipass as its multi-backend authentication library, which facilitates integration with various identity providers such as LDAP, OAuth2, SAML, and others. This architecture allows organizations to centralize their authentication processes while maintaining flexibility in how users are verified against different directory services or external systems. However, the complexity introduced by supporting multiple authentication backends creates potential attack surfaces if input validation is not rigorously enforced across all integration points.
A critical vulnerability was identified within Indico versions prior to 3.3.13, specifically related to an incomplete remediation of a previously disclosed issue designated as CVE-2026-25738. While earlier patches attempted to address security flaws involving URL handling and authentication redirects, they failed to account for specific edge cases where crafted URLs could bypass existing validation logic. This oversight allowed an authenticated event organizer to submit specially constructed URLs that pointed toward prohibited local targets or internal services. The vulnerability stems from insufficient sanitization of user-supplied input during the processing of these URLs, enabling the application to interpret maliciously formatted strings as legitimate authentication endpoints or redirect destinations.
The operational impact of this flaw is significant for organizations using Indico in multi-tenant environments where event organizers have elevated privileges within their respective events but should not possess access to internal infrastructure data. By exploiting this edge case, an attacker can leverage the application's own features to read sensitive data returned by local targets that are normally inaccessible from external networks or untrusted contexts. This effectively transforms a standard authentication feature into a mechanism for server-side request forgery-like behavior, allowing unauthorized disclosure of information stored on internal servers or services reachable only through localhost interfaces. The ability to exfiltrate this data compromises the confidentiality guarantees expected in secure event management deployments.
This vulnerability aligns with CWE-20 Improper Input Validation and CWE-918 Server-Side Request Forgery (SSRF) as it involves failing to properly validate user-controlled input before processing it through internal network resources. From a tactical perspective, this behavior corresponds to ATT&CK technique T1557 Adversary-in-the-Middle or potentially T1046 Network Service Discovery depending on the specific exploitation method used to probe local services. The flaw highlights the risks associated with complex authentication integrations where trust boundaries between external users and internal systems are not strictly enforced at every point of interaction.
To mitigate this risk, organizations must upgrade Indico to version 3.3.13 or later immediately upon availability. This release includes comprehensive fixes for the edge cases that were missed in previous patches, ensuring that all URL inputs undergo rigorous validation against a strict allowlist of permitted domains and protocols. Administrators should also review their current configurations to ensure no legacy authentication backends remain enabled if they are not actively used, thereby reducing the overall attack surface. Additionally implementing network-level controls such as firewall rules or reverse proxy configurations can further restrict access to internal services from application servers, providing defense-in-depth against similar SSRF-style vulnerabilities in other applications running on the same infrastructure.