CVE-2026-91981

Vikunja before 2.6.0 fails to properly restrict access to the link-share hash field in single-share read endpoints, allowing read-only members to obtain the share's secret credential. Attackers can exchange the disclosed hash for a link-share JWT at the share's permission level to escalate privileges and perform unauthorized writes or administrative actions.

Vikunja before 2.6.0 fails to validate that user-supplied project_view_id in task-position requests belongs to the task's project. Authenticated attackers can insert task position rows into arbitrary other tenant project views via POST or PUT task-position endpoints.

Vikunja before 2.6.0 contains an API token scope bypass vulnerability in task read endpoints where authorization fails to inspect query string parameters. Attackers with limited token scopes can use the expand parameter to access restricted data like comments, reactions, and time entries without proper permission verification.

Vikunja before 2.6.0 continues to expose the raw TOTP shared secret after enrollment through the GET /api/v1/user/settings/totp and /api/v1/user/settings/totp/qrcode endpoints without re-authentication. Attackers with a valid access token can read the secret, import it into their own authenticator, and generate valid codes indefinitely to defeat the second factor and enable account takeover.

vikunja before 2.6.0 fails to validate team access when attaching teams to projects, allowing authenticated users to enumerate all teams and members. Attackers can attach arbitrary team IDs via the project teams endpoint to retrieve complete team rosters including member names and admin flags for unauthorized teams.

Vikunja before 2.6.0 fails to limit archive expansion during data import, allowing authenticated users to cause denial of service. Attackers can upload highly compressed files that expand to tens of gigabytes in memory and disk, exhausting server resources and crashing the instance.

Vikunja before 2.6.0 contains an authentication bypass vulnerability in CalDAV BasicAuth endpoints that lack rate limiting protection. Remote unauthenticated attackers can issue unbounded credential-guessing requests against /dav, /.well-known, and /feeds routes to bypass the instance's anti-brute-force controls and compromise password-only accounts.

Vikunja versions before 2.6.0 fail to apply rate limiting to /api/v2 public authentication endpoints including login, register, password-reset, and OAuth token routes. Remote unauthenticated attackers can perform unbounded credential guessing, account enumeration, and password-reset flooding attacks without throttling restrictions.

Vikunja before 2.6.0 fails to apply pixel decode limits to avatar and project-background upload endpoints, allowing authenticated users to upload crafted images that decode to excessive pixel counts. Attackers can upload small images with extreme aspect ratios that consume significant CPU and memory during processing, causing denial of service through repeated or concurrent uploads.

Vikunja versions before 2.6.0 contain a resource exhaustion vulnerability in the Planka migrator that fails to enforce aggregate memory budgets during migration jobs. Authenticated attackers can submit migration requests pointing to attacker-controlled servers advertising numerous size-compliant attachments, exhausting worker memory and causing denial of service for all users.