CVE-2026-102927 in HedgeDoc
Summary
by MITRE • 11/05/2026
HedgeDoc is an open source, real-time collaborative markdown notes application. Prior to 1.11.1, the WebSocket permission handler allows a note owner to store strings outside the supported freely, editable, limited, locked, protected, and private permission values. The viewing and editing checks handle only known values and can otherwise fall through to permissive behavior, making a note readable or writable more broadly than intended. SQLite deployments can persist the invalid value because the database column does not strictly enforce the set, while MySQL and PostgreSQL reject the database update but can leave the in-memory note state inconsistent for connected users until reload or cache eviction. Exploitation requires the note owner to intentionally submit an invalid permission value, and the owner could already choose a legitimate permissive setting, which limits the practical security impact. This issue is fixed in version 1.11.1.
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Analysis
by VulDB Data Team • 11/05/2026
HedgeDoc is an open-source platform designed for real-time collaborative markdown note-taking, relying on strict permission models to control access and modification rights among users. The application defines a specific set of valid permission states including freely editable, limited, locked, protected, and private configurations. These values are intended to enforce granular access controls that dictate who can view or edit content within a shared document. However, prior to version 1.11.1, the WebSocket permission handler contained a logic flaw that allowed note owners to store string values outside this defined set of supported permissions. This vulnerability stems from insufficient input validation at the application layer when processing permission updates via WebSocket connections, enabling the persistence or in-memory storage of arbitrary strings rather than restricting inputs to the enumerated valid states.
The technical core of this issue lies in how viewing and editing checks are implemented within the HedgeDoc architecture. These security controls were designed to handle only known, predefined values explicitly listed in the codebase. When an invalid permission string was submitted by a note owner, the conditional logic failed to reject it or map it to a secure default state. Instead, the system allowed execution to fall through to permissive behavior. This means that if the stored value did not match any of the restricted categories such as locked or private, the application defaulted to allowing broader access than intended. Consequently, notes could become readable or writable by users who should have been denied access based on the owner's original intent, effectively bypassing the configured security boundaries through a logic error rather than a traditional buffer overflow or injection attack.
The operational impact of this vulnerability varies depending on the underlying database management system in use. In deployments utilizing SQLite, the invalid permission value could be persisted directly to the database because the column definition lacked strict enforcement mechanisms such as check constraints that would reject non-conforming values. This resulted in a persistent state where all connected users might perceive the note under incorrect access rules until an explicit correction was made. Conversely, MySQL and PostgreSQL deployments typically enforce stricter schema integrity or transactional consistency at the database level, causing them to reject invalid updates during the write operation. However, even in these robust environments, the application could leave the in-memory state of connected users inconsistent with the actual database record. This discrepancy means that until a user reloads their session or cache eviction occurs, they may continue operating under false assumptions about access rights, potentially leading to unauthorized data exposure or modification during that window of inconsistency.
From an exploitation perspective, this vulnerability requires the note owner to intentionally submit an invalid permission value through the WebSocket interface. It is not possible for external attackers to trigger this condition without first gaining ownership privileges over a specific document. Furthermore, because a note owner already possesses the ability to choose legitimate permissive settings such as freely editable or public access, the practical security impact of exploiting this flaw is significantly limited. The vulnerability essentially allows an attacker who has compromised or been granted owner rights to bypass certain granular restrictions by using non-standard values that slip through validation checks. While this represents a deviation from secure coding principles and introduces ambiguity into the permission model, it does not grant privileges beyond what could be achieved through legitimate configuration choices available in earlier versions.
To mitigate this risk, organizations running HedgeDoc must upgrade to version 1.11.1 or later where the WebSocket permission handler has been patched to strictly validate input against the allowed set of values. For environments that cannot immediately patch, administrators should ensure that database schemas include strict check constraints on permission columns to prevent invalid states from being persisted regardless of application-layer validation failures. Additionally, implementing robust cache eviction policies and session refresh mechanisms can help reduce the window of inconsistency in memory-based state discrepancies particularly for MySQL and PostgreSQL deployments. Security teams should also review access control lists within HedgeDoc instances to ensure that no sensitive documents rely solely on implicit trust assumptions rather than explicit restrictive configurations. This incident highlights the importance of enforcing strict input validation at both the application logic layer and the database schema level to prevent privilege escalation through configuration manipulation. The vulnerability aligns with CWE-20 Improper Input Validation as it involves failing to verify that user-supplied data conforms to expected formats or values, leading to unintended system behavior. It also relates to ATT&CK technique T1534 Internal Spearphishing in the context of social engineering if an attacker tricks a legitimate owner into submitting malicious configurations, although direct exploitation is limited by the requirement for existing ownership privileges.