GHSA-w2ch-4xgr-22ww GO-2026-6754

Vikunja: Task relation deletion does not check read access to the other task, allowing cross-project relation removal

Low Go

Severity: 0.0 / 10; Low · CVSS 4.0
Exploit chance (EPSS): —; No score published
Known exploited: No; Not in CISA's catalog
Weakness: CWE-285 Improper Authorization; CWE-862 Missing Authorization
Fix: 2.6.0; Upgrade code.vikunja.io/api to this version or later

Description

Summary

Deleting a task relation only requires write access on the base task. Unlike relation creation, it does not verify that the caller can read the other task. A user with write access to one project can therefore delete relations whose other end lives in a project they have no access to. Since the delete removes both the forward and inverse rows, the relation also disappears for the other project's members.

Details

TaskRelation.CanCreate (pkg/models/task_relation_permissions.go:32-52) requires write access on TaskID and read access on OtherTaskID.

TaskRelation.CanDelete (pkg/models/task_relation_permissions.go:25-29) only checks Task{ID: rel.TaskID}.CanUpdate(s, a); OtherTaskID is never authorized.

TaskRelation.Delete (pkg/models/task_relation.go:314-354) then deletes both the (task_id, other_task_id, kind) row and its inverse, so the relation is removed from the far task as well.

Affects DELETE /api/v1/tasks/{id}/relations/{kind}/{otherTaskId} and the equivalent v2 endpoint.

Impact

Low, integrity only. An authenticated user holding write permission on a shared project can remove task relations that link into projects they cannot read. No data is disclosed and no privilege is gained; the attacker cannot recreate the relation. The far project's owner sees the relation vanish without indication of who removed it.

Preconditions: the attacker has write access to a project containing a task that is already related to a task in a project they cannot access.

Proof of Concept

As owner, create project P_near with task near and project P_far with task far.
Share P_near with attacker at write permission (permission: 1). Do not share P_far.
As owner: PUT /api/v1/tasks/{near}/relations with {"other_task_id": far, "relation_kind": "related"} -> 200.
As attacker: GET /api/v1/tasks/{far} -> 403 (confirms no access).
As attacker: PUT /api/v1/tasks/{near}/relations with the same body -> 403 (create path is enforced).
As attacker: DELETE /api/v1/tasks/{near}/relations/related/{far} -> 200 "Successfully deleted."
As owner: GET /api/v1/tasks/{far} -> related_tasks is now empty.

Reproduced against vikunja/vikunja:2.5.0.

Recommended Fix

Make CanDelete mirror CanCreate: after checking CanUpdate on the base task, also require CanRead on OtherTaskID.

Affected versions

Go

Package	Vulnerable	Fixed in
code.vikunja.io/api	`>= 0.9, < 2.6.0`	`2.6.0`
code.vikunja.io/api	`all versions`	No fix yet

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

code.vikunja.io/api Go → `2.6.0`

go

go get code.vikunja.io/api@v2.6.0 && go mod tidy

Severity breakdown

CVSS 4.0 0.0

CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N

Attack vector: Network
Attack complexity: Low
Attack requirements: Present
Privileges required: Low
User interaction: None
Confidentiality (vulnerable system): None
Integrity (vulnerable system): Low
Availability (vulnerable system): None
Confidentiality (subsequent systems): None
Integrity (subsequent systems): None
Availability (subsequent systems): None

Weakness

CWE-285: Improper Authorization

The product does not perform or incorrectly performs an authorization check when an actor attempts to access a resource or perform an action.

How to prevent it

Architecture and Design: Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) to enforce the roles at the appropriate boundaries. Note that this approach may not protect against horizontal authorization, i.e., it will not protect a user from attacking others with the same role.
Architecture and Design: Ensure that you perform access control checks related to your business logic. These checks may be different than the access control checks that you apply to more generic resources such as files, connections, processes, memory, and database records. For example, a database may restrict access for medical records to a specific database user, but each record might only be intended to be accessible to the patient and the patient's doctor.
Architecture and Design: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, consider using authorization frameworks such as the JAAS Authorization Framework [REF-233] and the OWASP ESAPI Access Control feature [REF-45].
Architecture and Design: For web applications, make sure that the access control mechanism is enforced correctly at the server side on every page. Users should not be able to access any unauthorized functionality or information by simply requesting direct access to that page. One way to do this is to ensure that all pages containing sensitive information are not cached, and that all such pages restrict access to requests that are accompanied by an active and authenticated session token associated with a user who has the required permissions to access that page.
System Configuration, Installation: Use the access control capabilities of your operating system and server environment and define your access control lists accordingly. Use a "default deny" policy when defining these ACLs.

CWE-862: Missing Authorization

The product does not perform an authorization check when an actor attempts to access a resource or perform an action.

How to prevent it

Architecture and Design: Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) [REF-229] to enforce the roles at the appropriate boundaries. Note that this approach may not protect against horizontal authorization, i.e., it will not protect a user from attacking others with the same role.
Architecture and Design: Ensure that access control checks are performed related to the business logic. These checks may be different than the access control checks that are applied to more generic resources such as files, connections, processes, memory, and database records. For example, a database may restrict access for medical records to a specific database user, but each record might only be intended to be accessible to the patient and the patient's doctor [REF-7].
Architecture and Design: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, consider using authorization frameworks such as the JAAS Authorization Framework [REF-233] and the OWASP ESAPI Access Control feature [REF-45].
Architecture and Design: For web applications, make sure that the access control mechanism is enforced correctly at the server side on every page. Users should not be able to access any unauthorized functionality or information by simply requesting direct access to that page. One way to do this is to ensure that all pages containing sensitive information are not cached, and that all such pages restrict access to requests that are accompanied by an active and authenticated session token associated with a user who has the required permissions to access that page.
System Configuration, Installation: Use the access control capabilities of your operating system and server environment and define your access control lists accordingly. Use a "default deny" policy when defining these ACLs.

References

Packages

github.com/go-vikunja/vikunja

Timeline

Oct 9, 2026 Published
Oct 19, 2026 Last updated by the source

Advisory	Severity	Why it's related
GHSA-m687-p538-r5hp Vikunja: Permissive Cross-domain Security Policy trusts every localhost origin which should not be trusted	Medium	Also affects code.vikunja.io/api
GHSA-fmmf-xq98-g327 Vikunja: Write-level project members can delete admin-tier link shares through an unloaded permission check	Medium	Also affects code.vikunja.io/api
GHSA-pjr3-86v4-5p7w Vikunja: Explicit lower-permission share on a sub-project is silently overridden by an inherited parent permission (broken access control / privilege-management regression in v2.6.0)	Medium	Also affects code.vikunja.io/api
GHSA-hjx8-qv73-f7cm Vikunja: Webhooks and link shares survive every revocation path, so a removed collaborator keeps a live feed	High	Also affects code.vikunja.io/api
GHSA-fprf-r6rv-xg99 Vikunja: Saved filter creation with an empty filter string recalculates task positions across all tenants	Medium	Also affects code.vikunja.io/api
GHSA-4hv6-xc92-j86g Vikunja: WebSocket authentication ignores server-side session state, so revoked sessions keep receiving live pushes	High	Also affects code.vikunja.io/api
GHSA-8wvg-r2j4-3737 Vikunja: Assignee email addresses disclosed to read-only project members via the task assignees endpoint	Medium	Also affects code.vikunja.io/api
GHSA-3hc7-r24j-rpwc Vikunja: Cross-project task disclosure through subtask expansion	Medium	Also affects code.vikunja.io/api

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