Skip to content

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

Low severity GitHub Reviewed Published Aug 31, 2026 in go-vikunja/vikunja

Package

gomod code.vikunja.io/api (Go)

Affected versions

>= 0.9, <= 2.5.0

Patched versions

2.6.0

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

  1. As owner, create project P_near with task near and project P_far with task far.
  2. Share P_near with attacker at write permission (permission: 1). Do not share P_far.
  3. As owner: PUT /api/v1/tasks/{near}/relations with {"other_task_id": far, "relation_kind": "related"} -> 200.
  4. As attacker: GET /api/v1/tasks/{far} -> 403 (confirms no access).
  5. As attacker: PUT /api/v1/tasks/{near}/relations with the same body -> 403 (create path is enforced).
  6. As attacker: DELETE /api/v1/tasks/{near}/relations/related/{far} -> 200 "Successfully deleted."
  7. 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.

References

@kolaente kolaente published to go-vikunja/vikunja Aug 31, 2026
Published to the GitHub Advisory Database Oct 9, 2026
Reviewed Oct 9, 2026

Severity

Low

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements Present
Privileges Required Low
User interaction None
Vulnerable System Impact Metrics
Confidentiality None
Integrity Low
Availability None
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
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

EPSS score

Weaknesses

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. Learn more on MITRE.

Missing Authorization

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

CVE ID

No known CVE

GHSA ID

GHSA-w2ch-4xgr-22ww

Source code

Credits

Loading Checking history
See something to contribute? Suggest improvements for this vulnerability.