CVE-2026-111920 in Vikunja
Summary
by MITRE • 10/17/2026
Vikunja 2.6.0 contains a broken access control flaw in getProjectAccessForUser (pkg/models/project_access.go), which resolves a user's effective project permission as the maximum over the project tree, silently overriding explicit lower-permission shares on sub-projects. A collaborator with write access on a parent project but read-only access to a child project can modify the child project's tasks and content.
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Analysis
by VulDB Data Team • 10/17/2026
The vulnerability identified in Vikunja version 2.6.0 represents a critical failure in role-based access control mechanisms, specifically within the logic that resolves effective permissions for users interacting with hierarchical project structures. The flaw resides in the getProjectAccessForUser function located in pkg/models/project_access.go. This component is responsible for determining what actions a specific user is authorized to perform on a given resource by aggregating permission data from various sources. In this instance, the implementation incorrectly calculates effective permissions by taking the maximum value across all levels of the project tree hierarchy rather than respecting explicit denials or lower-level restrictions defined at more granular scopes. This approach fundamentally violates the principle of least privilege and fails to account for the specificity of access control lists when conflicts arise between parent and child resource definitions.
From a technical perspective, the core issue is an incorrect permission resolution algorithm that prioritizes breadth over precision. When a user has write access granted at the level of a parent project, the system erroneously propagates this high-level privilege down to all sub-projects, regardless of any explicit read-only or no-access restrictions applied directly to those child projects. This silent override means that security policies defined at lower levels are effectively nullified by permissions established higher up in the hierarchy. The logic does not perform a check for explicit deny rules or more restrictive settings on specific nodes within the tree structure. Consequently, the access control model becomes inconsistent with standard expectations where granular controls should take precedence over broader group-based grants when they conflict.
The operational impact of this vulnerability is significant and directly affects data integrity and confidentiality within multi-tenant task management environments. An attacker or malicious insider who possesses write permissions on a parent project can exploit this flaw to modify, delete, or create tasks in child projects where they are explicitly granted only read-only access. This bypasses intended security boundaries, allowing unauthorized modifications to content that should be protected from such changes. In collaborative workflows, this could lead to accidental data loss if users inadvertently alter restricted items, or it could enable malicious actors to inject misleading information into sensitive sub-projects without detection by standard audit logs that might only record the action as a legitimate write operation on the parent scope.
This vulnerability aligns with Common Weakness Enumeration category CWE-269, which covers Improper Privilege Management, and more specifically reflects issues related to access control logic errors often categorized under CWE-862 Missing Authorization or CWE-732 Incorrect Permission Assignment for Critical Resource. In terms of the MITRE ATT&CK framework, this behavior facilitates lateral movement within an application's data structure by allowing a user with limited privileges on specific resources to escalate their effective rights through hierarchical traversal. It represents a classic case where permission inheritance is implemented incorrectly, leading to privilege escalation relative to the intended security policy for nested objects.
Mitigation strategies must focus on correcting the permission resolution logic in the getProjectAccessForUser function. The system should be updated to evaluate permissions starting from the most specific resource level upward, ensuring that explicit restrictions at lower levels are respected and not overridden by broader parent-level grants. Implementing a deny-override policy model is essential, where any explicit denial or restriction on a child project takes precedence over inherited allowances from its ancestors. Additionally, comprehensive unit tests should be added to verify permission resolution across various hierarchical configurations, including scenarios with conflicting permissions at different tree levels. Regular security code reviews focusing on access control lists and inheritance logic are recommended to prevent similar flaws in future development cycles.