CVE-2026-109206 in Community Edition
Summary
by MITRE • 10/12/2026
LogicalDOC Community Edition through 9.3 contains a username enumeration vulnerability that allows unauthenticated attackers to identify valid accounts because the AvatarServlet (/avatar) performs no session validation. Attackers can supply usernames or numeric IDs in the userId parameter and compare 1x1 transparent images against real avatars to enumerate users and retrieve profile pictures.
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Analysis
by VulDB Data Team • 10/12/2026
The LogicalDOC Community Edition, specifically versions up through 9.3, suffers from a critical information disclosure vulnerability rooted in improper session validation within its AvatarServlet component. This flaw allows unauthenticated attackers to perform username enumeration by exploiting the application's avatar retrieval mechanism. The core technical issue lies in the lack of authentication or authorization checks when processing requests directed at the /avatar endpoint. Because this servlet does not verify whether the requesting user has an active, valid session or appropriate permissions to access specific resources, it treats all incoming requests for avatar data as legitimate regardless of their origin. This architectural oversight creates a direct pathway for malicious actors to probe the system and extract sensitive identity information without needing prior credentials.
The operational mechanics of this vulnerability involve manipulating the userId parameter within HTTP requests sent to the AvatarServlet. Attackers can supply arbitrary usernames or numeric user identifiers in this field, prompting the server to attempt retrieving the corresponding profile picture. The exploitation technique relies on a visual comparison method where attackers request avatars for various potential users and analyze the response data. Specifically, they compare 1x1 transparent images against actual avatar files. If the system returns an image that is not the default placeholder or empty state, it indicates that a valid account exists with that specific identifier. This side-channel approach effectively transforms a simple file retrieval function into a powerful user enumeration tool, allowing attackers to map out the organization's internal user base and identify active accounts for further targeting.
The impact of this vulnerability extends beyond mere identity exposure. By successfully enumerating valid usernames, adversaries can significantly lower the barrier for subsequent attacks such as credential stuffing or brute-force password guessing campaigns. Knowing which accounts are active allows attackers to focus their efforts on high-value targets rather than wasting resources on non-existent users. Furthermore, retrieving profile pictures may provide additional contextual intelligence about the organization's structure and personnel, aiding in social engineering initiatives. This vulnerability aligns with CWE-203, which describes observable discrepancy that can be exploited for information disclosure, as well as CWE-613 regarding insufficient session expiration or management practices that fail to protect sensitive endpoints from unauthorized access.
From a threat intelligence perspective, this behavior is consistent with techniques documented in the MITRE ATT&CK framework under Information Gathering, specifically T1087 Account Discovery and potentially T1592 Gather Victim Host Information if used to map organizational structures. The lack of session validation on public-facing or semi-public endpoints represents a fundamental security design flaw that violates basic principles of secure software development. To mitigate this risk, developers must implement strict access control checks within the AvatarServlet to ensure that only authenticated and authorized users can retrieve avatar data based on their own identity or explicit permission grants. Additionally, implementing rate limiting and monitoring for unusual patterns in request frequency can help detect and block automated enumeration attempts before they yield significant intelligence gains.