CVE-2021-41809 in Server
Summary
by MITRE • 01/18/2022
SSRF vulnerability in M-Files Server products with versions before 22.1.11017.1, in a preview function allowed making queries from the server with certain document types referencing external entities.
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Analysis
by VulDB Data Team • 02/23/2026
The CVE-2021-41809 vulnerability represents a critical server-side request forgery flaw discovered in M-Files Server products affecting versions prior to 22.1.11017.1. This vulnerability specifically targets the preview function within the document management system, creating a pathway for malicious actors to exploit the server's ability to make external network requests. The flaw stems from insufficient input validation and sanitization mechanisms that allow unauthorized entities to manipulate the preview functionality to access internal network resources or external systems that should otherwise remain isolated from the server environment.
The technical implementation of this vulnerability involves the preview function's handling of document metadata and references, particularly when processing certain document types that contain external resource pointers. When the server attempts to generate previews for documents containing these references, it fails to properly validate or restrict the external entities that can be accessed, enabling attackers to craft malicious requests that bypass normal network security controls. This behavior aligns with CWE-918, which describes server-side request forgery vulnerabilities where applications fetch resources from external systems based on user-supplied input without adequate validation. The vulnerability's exploitation requires minimal privileges since it operates within the server's own context, making it particularly dangerous as it can leverage the server's network access rights to probe internal systems.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides attackers with potential access to internal network resources, sensitive data repositories, and other systems within the server's network scope. Attackers can potentially enumerate internal services, access databases, or even escalate their access to other systems within the network perimeter by exploiting the preview function's external reference handling. This threat model aligns with several ATT&CK techniques including T1071.004 for application layer protocol usage and T1046 for network service scanning, as the vulnerability enables reconnaissance activities that would normally be restricted by network segmentation and firewall rules. The server's role as a central document management platform amplifies the potential damage since it often contains sensitive business documents and may have access to various internal systems through its operational requirements.
Mitigation strategies for CVE-2021-41809 should focus on immediate patching of affected M-Files Server versions to 22.1.11017.1 or later, which includes fixed validation mechanisms for the preview function's external reference handling. Organizations should implement network segmentation controls to limit the server's access to external resources and establish strict firewall rules that prevent unauthorized outbound connections from the server environment. Additional protective measures include implementing web application firewalls to monitor and filter requests to the preview functionality, conducting thorough code reviews of document processing functions, and establishing network monitoring protocols to detect unusual outbound connections from the server. Security teams should also consider implementing principle of least privilege controls for the server's network access rights, ensuring that the server can only access necessary external resources for legitimate document preview operations while blocking access to internal network segments. The vulnerability demonstrates the importance of validating all external references in server-side applications and implementing proper input sanitization mechanisms to prevent unauthorized resource access patterns.