Summary
Vikunja: Write-level project members can delete admin-tier link shares through an unloaded permission check
A project member with Write permission can delete an admin-tier link share on that project. The deletion authorization check reads the permission from an object populated only with URL IDs, rather than from the stored share. Its zero value is Read, so the check falls through to project Write permission instead of requiring Admin.
Details
Affected endpoints:
DELETE /api/v1/projects/{project}/shares/{share}DELETE /api/v2/projects/{project}/shares/{share}
Older v1 releases used /lists/{list}/shares/{share} before lists were renamed to projects.
In pkg/routes/api/v2/link_sharing.go:156, the delete handler passes &models.LinkSharing{ID: in.ID, ProjectID: in.ProjectID} to handler.DoDelete. The v1 generic handler likewise binds the URL IDs without loading the stored share.
pkg/web/handler/core.go:185 calls CanDelete before Delete. LinkSharing.CanDelete delegates to canDoLinkShare in pkg/models/link_sharing_permissions.go. That helper loads the project but does not load the link share, then evaluates:
if share.Permission == PermissionAdmin {
return l.IsAdmin(s, a)
}
return l.CanWrite(s, a)
On deletion, share.Permission is its Go zero value, PermissionRead (0), even when the stored share grants PermissionAdmin (2). A Write member therefore passes authorization. LinkSharing.Delete subsequently deletes by share ID and project ID without checking the stored permission.
Create uses the requested permission and correctly rejects Write members creating admin shares. Share listing and by-ID reads are admin-gated in current main. There is no HTTP update route for link shares. Read-only members and link-share principals are rejected on deletion.
Affected versions and verification
The admin-tier check was introduced in commit 56dbb564eae83f2453efd1049f55e9d099b5d346, first included in v0.13, without loading the stored share on deletion. The affected range established by this review is >= 0.13.0, <= 2.6.0; versions before v0.13 have not been assessed here. The v2 route was added in b10768506, first included in v2.4.0.
The reporter states that both API versions were verified live against a local source build at a881ac39eecd07575a5aede8e74727c28d5fd578 on September 7, 2026. Maintainer-side source review confirmed the mechanism in that commit, release v2.6.0, and upstream main at a1a6ca48be142902f09fee62734310cb98a8c414. The live proof of concept was not independently rerun during this triage. No patched version is available at draft creation.
Proof of concept
Use two regular accounts on an instance you control. Let OWNER_TOKEN and WRITER_TOKEN be their session tokens. Create a project as the owner, grant the second account Write permission (permission: 1), and create an admin-tier share as the owner (permission: 2). Let PROJECT_ID and SHARE_ID identify that project and share.
First, verify that the Write member cannot create an admin-tier share:
curl -i -X POST "$BASE/api/v2/projects/$PROJECT_ID/shares" \
-H "Authorization: Bearer $WRITER_TOKEN" \
-H 'Content-Type: application/json' \
-d '{"permission":2}'
# Expected and reported: 403
Delete the owner's admin-tier share as the same Write member:
curl -i -X DELETE "$BASE/api/v2/projects/$PROJECT_ID/shares/$SHARE_ID" \
-H "Authorization: Bearer $WRITER_TOKEN"
# Reported: 204; expected: 403 and the share remains intact
Recreate the admin-tier share as the owner and repeat with the v1 endpoint:
curl -i -X DELETE "$BASE/api/v1/projects/$PROJECT_ID/shares/$SHARE_ID" \
-H "Authorization: Bearer $WRITER_TOKEN"
# Reported: 200 with {"message":"Successfully deleted."}; expected: 403
With the collaborator downgraded to Read, deletion returns 403. These positive and negative controls were reported as verified live by the reporter.
Related advisories
- GHSA-f95f-77jx-fcjc / CVE-2026-33700 addressed cross-project deletion. Fix
654d2c704constrained deletion byproject_idbut did not change the permission-tier check. - GHSA-qfwc-vx6f-3g6g addressed share-hash disclosure through by-ID reads.
- GHSA-8hp8-9fhr-pfm9 addressed share-hash disclosure through listing.
- GHSA-96q5-xm3p-7m84 / CVE-2026-35594 addressed tokens remaining valid after deletion. That fix does not prevent unauthorized deletion.
Credit
Reported via mail.
Impact
A Write collaborator can revoke an admin-tier access link on a project they can already write to. New consumers can no longer authenticate with that link. In versions with database-backed link-share JWT validation, deleting the share also immediately invalidates its existing sessions; the reporter observed HTTP 404 for a new hash exchange and HTTP 401 for an existing share token.
This is a bounded integrity and availability impact on external access to that project. It does not disclose data, grant Admin privileges, allow deletion of another project's shares, or permit the attacker to create a replacement admin share. The attacker must know or guess the numeric share ID; IDs are sequential.
Severity: Medium. CWE-863: Incorrect Authorization.
The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions. Typical impact: unauthorized data access or execution of privileged operations.
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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For deletion, load the stored share scoped to both the requested share ID and project ID before authorizing. Require project Admin when the stored permission is Admin, and retain the intended Write rule for ordinary read/write shares. Preserve the existing cross-project constraint.
Keep creation authorization based on the requested tier. If update support is added, check both the stored tier and the requested new tier so neither demotion nor promotion can bypass the admin check.
Add regression coverage for a Write member being forbidden to delete an admin-tier share, an Admin being allowed, intended ordinary-share deletion, rejection of Read members and link-share principals, and mismatched project/share IDs. Cover both API versions.
Frequently Asked Questions
- What is GHSA-FMMF-XQ98-G327? GHSA-FMMF-XQ98-G327 is a medium-severity incorrect authorization vulnerability in code.vikunja.io/api (go), affecting versions >= 0.13.0, <= 2.6.0. It is fixed in 2.7.0. The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions.
- Which versions of code.vikunja.io/api are affected by GHSA-FMMF-XQ98-G327? code.vikunja.io/api (go) versions >= 0.13.0, <= 2.6.0 is affected.
- Is there a fix for GHSA-FMMF-XQ98-G327? Yes. GHSA-FMMF-XQ98-G327 is fixed in 2.7.0. Upgrade to this version or later.
- Is GHSA-FMMF-XQ98-G327 exploitable, and should I be worried? Whether GHSA-FMMF-XQ98-G327 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-FMMF-XQ98-G327 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-FMMF-XQ98-G327? Upgrade
code.vikunja.io/apito 2.7.0 or later.