CVE-2020-26286 in HedgeDoc
Summary
by MITRE • 12/29/2020
HedgeDoc is a collaborative platform for writing and sharing markdown. In HedgeDoc before version 1.7.1 an unauthenticated attacker can upload arbitrary files to the upload storage backend including HTML, JS and PHP files. The problem is patched in HedgeDoc 1.7.1. You should however verify that your uploaded file storage only contains files that are allowed, as uploaded files might still be served. As workaround it's possible to block the `/uploadimage` endpoint on your instance using your reverse proxy. And/or restrict MIME-types and file names served from your upload file storage.
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Analysis
by VulDB Data Team • 05/09/2026
The vulnerability in HedgeDoc prior to version 1.7.1 represents a critical security flaw that allows unauthenticated attackers to upload arbitrary files to the platform's storage backend. This issue stems from insufficient validation mechanisms within the file upload functionality, creating an environment where malicious actors can bypass authentication requirements and directly interact with the upload storage system. The vulnerability specifically affects the `/uploadimage` endpoint which lacks proper access controls and file type restrictions, enabling attackers to submit potentially harmful file types including html javascript and php scripts.
From a technical perspective this represents a classic insecure file upload vulnerability that maps to CWE-434 which describes the improper restriction of uploads to a restricted directory. The flaw allows attackers to bypass normal file validation procedures and store malicious content directly in the platform's storage backend. This creates multiple attack vectors as the uploaded files remain accessible through the platform's serving mechanisms, potentially allowing for cross-site scripting attacks, server-side request forgery, or other malicious activities depending on the file types uploaded. The vulnerability is particularly dangerous because it operates without authentication requirements, making it accessible to anyone with network access to the HedgeDoc instance.
The operational impact of this vulnerability extends beyond simple file storage compromise. Attackers can leverage this flaw to execute arbitrary code on the server, potentially leading to complete system compromise. When combined with the fact that uploaded files remain accessible through the platform, this creates a persistent threat vector that could allow attackers to maintain access or launch further attacks against the platform and its users. The vulnerability affects all versions prior to 1.7.1 and represents a significant risk for organizations relying on HedgeDoc for collaborative documentation, as it could lead to data breaches, service disruption, or unauthorized access to sensitive information.
The patch implemented in HedgeDoc version 1.7.1 addresses the core issue by introducing proper authentication checks and enhanced file validation mechanisms. However, security practitioners must implement additional defensive measures to ensure complete protection. Organizations should conduct thorough audits of their existing upload storage directories to identify and remove any potentially malicious files that may have been uploaded during the vulnerable period. The recommended workaround of blocking the `/uploadimage` endpoint through reverse proxy configuration provides an effective immediate mitigation strategy. Additionally implementing strict MIME-type validation and filename filtering on the upload storage serves as a secondary defense layer that prevents malicious files from being stored or served. These measures align with ATT&CK technique T1195 which covers content injection attacks and emphasize the importance of proper input validation and access controls in preventing unauthorized file operations.