CVE-2026-91983: Vikunja before 2.6.0 API Token Scope Bypass via expand Parameter

Severity: medium (CVSS 4.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-09-15 · updated 2026-09-16
Weakness: CWE-863

Description

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.

Affected products

go-vikunja vikunja: from 1.0.0 before 2.6.0 — fixed in 2.6.0

How to fix

Upgrade to a fixed version: go-vikunja vikunja 2.6.0. Check the vendor advisory for mitigations.

References

https://github.com/go-vikunja/vikunja/security/advisories/GHSA-9rg3-v78m-26q8
https://www.vulncheck.com/advisories/vikunja-before-2.6.0-api-token-scope-bypass-via-expand-parameter
https://github.com/go-vikunja/vikunja/security/advisories/GHSA-9rg3-v78m-26q8

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