Vikunja: Link-share principal-type confusion enables cross-account team removal, bot takeover, and roster disclosure

{
  "id": "a7027153b7f3838d8fc7d4bc114e101f051bf133d43d1ee79374acef628ecb2f",
  "url": "https://osv.dev/vulnerability/GHSA-32r8-5843-4qw2",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Vikunja: Link-share principal-type confusion enables cross-account team removal, bot takeover, and roster disclosure",
    "summary": "## Summary Vikunja's `web.Auth` interface (`pkg/web/web.go`, single method `GetID() int64`) is satisfied by BOTH `*user.User` and `*models.LinkSharing`. A link-share's `GetID()` returns the **raw positive** `share.ID` (`pkg/models/link_sharing.go:83-85`), which lives in the same positive autoincrement ID space as `users.id`. The safe negated form `getUserID() = share.ID * -1` (`link_sharing.go:126-128`) exists but is NOT used at three permission sinks. As a result, a link-share principal with id `N` — which should have zero authority over teams or bot users — is treated as the *user* whose `users.id == N` at three permission checks that lack the `a.(*LinkSharing)` guard their sibling methods have. This is the same principal-type-confusion class as CVE-2026-68581 (GHSA-vvcv-vpph-h844), but at three code paths that advisory/fix never touched. ## Root Cause `web.Auth` is a one-method interface (`GetID() int64`). `*LinkSharing.GetID()` returns the raw positive share id. Three permission methods compare this raw id directly and omit the link-share type guard used elsewhere in the same files: 1. **`TeamMember.CanDelete`** (`pkg/models/team_members_permissions.go:31-40`): the self-removal fast path `if u.ID == a.GetID() { return true }` (:36) executes **before** `IsAdmin`. `IsAdmin` (:48-51) is the ONLY place that rejects link shares (`if _, is := a.(*LinkSharing); is { return false }`, :50) — and it is never reached when the fast path returns true. 2. **`BotUser.isOwner`** (`pkg/mo",
    "evidence": "osv:GHSA-32r8-5843-4qw2",
    "products": [
      {
        "name": {
          "value": "code.vikunja.io/api",
          "evidence": "/affected/0/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "2.5.0",
            "evidence": "/affected/0/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "GHSA-32r8-5843-4qw2",
      "aliases": [
        "CVE-2026-76216",
        "GHSA-32r8-5843-4qw2",
        "GO-2026-6711"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "type": "SEMVER",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "2.5.0"
                }
              ]
            }
          ],
          "package": {
            "name": "code.vikunja.io/api",
            "purl": "pkg:golang/code.vikunja.io/api",
            "ecosystem": "Go"
          },
          "database_specific": {
            "source": "https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/10/GHSA-32r8-5843-4qw2/GHSA-32r8-5843-4qw2.json"
          }
        }
      ],
      "modified": "2026-10-27T15:30:05.146149430Z",
      "provider": "osv",
      "references": [
        "https://github.com/go-vikunja/vikunja/security/advisories/GHSA-32r8-5843-4qw2",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-76216",
        "https://github.com/go-vikunja/vikunja/commit/a717d64d5658708ba390f18dd697f5e567e68aac",
        "https://github.com/go-vikunja/vikunja",
        "https://github.com/go-vikunja/vikunja/releases/tag/v2.5.0",
        "https://www.vulncheck.com/advisories/vikunja-through-principal-type-confusion-via-linksharing"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-639",
          "CWE-843",
          "CWE-863"
        ],
        "severity": "HIGH",
        "github_reviewed": true,
        "nvd_published_at": null,
        "github_reviewed_at": "2026-10-09T20:43:40Z"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-76216",
        "evidence": "/aliases"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/database_specific/severity"
  },
  "source_id": "core-osv",
  "document_id": 462572,
  "published_at": "2026-10-09T20:43:40+00:00"
}