Summary
Vikunja: CalDAV relation creation bypasses TaskRelation.CanCreate, allowing an unauthorized write into any task by known UID
Creating a task relation over CalDAV does not run the TaskRelation.CanCreate permission check that the REST API enforces. An attacker can attach a relation to any task whose UID they know, including tasks in projects they have no access to. The identical operation over REST is correctly refused with 403.
Details
persistRelations (pkg/routes/caldav/listStorageProvider.go, ~line 986) resolves the related task with an unscoped UID lookup (models.GetTaskSimpleByUUID) and calls rel.Create(s, a) directly, with no CanCreate check. pkg/caldav/parsing.go maps RELATED-TO;RELTYPE=CHILD to RelationKindSubtask. Because the CalDAV path never invokes the model's permission method, an authenticated user can create a subtask/parent relation between a task they own and an arbitrary victim task identified only by its UID.
Task UIDs are json:"-" (never exposed over REST) but are exposed over CalDAV to anyone who has ever had read access to the containing project. Revoking that access does not unlearn the UID, so the realistic attacker is a removed collaborator.
This write primitive also feeds the cross-project subtask-disclosure issue (GHSA-3hc7-r24j-rpwc): it lets an attacker create the very cross-project subtask edge that read path leaks across, removing that finding's "the attacker cannot create one to a project they can't access" precondition.
A secondary effect of the same unchecked path: the createDummy branch can Create a task unchecked when the referenced UID does not resolve.
PoC (verified at runtime against v2.5.0, commit c775a6c8)
Baseline control, REST refuses:
PUT /api/v1/tasks/{attackerTask}/relations (attacker JWT)
{"task_id":{attackerTask},"other_task_id":{victimTask},"relation_kind":"subtask"}
-> HTTP 403 Forbidden
Exploit, CalDAV succeeds:
PUT /dav/projects/{attackerProject}/{attackerTaskUID}.ics (BasicAuth attacker)
BEGIN:VCALENDAR
VERSION:2.0
BEGIN:VTODO
UID:{attackerTaskUID}
RELATED-TO;RELTYPE=CHILD:{victimTaskUID}
END:VTODO
END:VCALENDAR
-> HTTP 201
Result: a task_relations row is written with task_id={victimTask}, relation_kind=parenttask, created_by_id={attacker}, a persisted, attacker-attributable write onto a task in a project the attacker cannot access.
Impact
Broken access control (missing authorization) on relation creation. An attacker can pollute the relation set of arbitrary tasks by UID and create the cross-project edges that enable subtask disclosure. Read of the related task's contents still requires the separate disclosure path; this finding is the unauthorized write.
The application does not perform an authorization check before performing a sensitive operation. Typical impact: unauthorized access to restricted functionality or data.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Route CalDAV relation creation through TaskRelation.CanCreate, and scope the UID lookup to projects the caller can access.
Frequently Asked Questions
- What is GHSA-G38J-7V97-X298? GHSA-G38J-7V97-X298 is a medium-severity missing authorization vulnerability in code.vikunja.io/api (go), affecting versions <= 2.5.0. It is fixed in 2.6.0. The application does not perform an authorization check before performing a sensitive operation.
- Which versions of code.vikunja.io/api are affected by GHSA-G38J-7V97-X298? code.vikunja.io/api (go) versions <= 2.5.0 is affected.
- Is there a fix for GHSA-G38J-7V97-X298? Yes. GHSA-G38J-7V97-X298 is fixed in 2.6.0. Upgrade to this version or later.
- Is GHSA-G38J-7V97-X298 exploitable, and should I be worried? Whether GHSA-G38J-7V97-X298 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether GHSA-G38J-7V97-X298 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix GHSA-G38J-7V97-X298? Upgrade
code.vikunja.io/apito 2.6.0 or later.