# CVE-2026-91973

## Summary

- **CVE ID:** CVE-2026-91973
- **Severity:** HIGH
- **CVSS Score:** 8.7 (CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N)
- **CWE:** CWE-307
- **Published:** Sep 15, 2026
- **Last Modified:** Sep 15, 2026

## Description

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.

## Affected Products

- go-vikunja — vikunja (0)
- go-vikunja — vikunja (2.6.0)

## References

- [CNA](https://github.com/go-vikunja/vikunja/security/advisories/GHSA-m469-88xx-8rx2)
- [CNA](https://www.vulncheck.com/advisories/vikunja-before-2.6.0-authentication-bypass-via-caldav-basicauth)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.61%
- **EPSS Percentile:** 47.6

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-18._