CVE-2026-91973
Received Received - Intake

Authentication Bypass in Vikunja CalDAV Endpoints

Publication date: 2026-09-15

Last updated on: 2026-09-15

Assigner: VulnCheck

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.

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Meta Information

Published
2026-09-15
Last Modified
2026-09-15
Generated
2026-09-15
AI Q&A
2026-09-15
EPSS Evaluated
N/A
NVD
CVE-2026-91973
EUVD
EUVD-2026-78649

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
vikunja vikunja to 2.6.0 (exc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-307 The product does not implement sufficient measures to prevent multiple failed authentication attempts within a short time frame.

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Executive Summary

Vikunja before version 2.6.0 has an authentication bypass flaw in its CalDAV BasicAuth endpoints. These endpoints do not have rate limiting, allowing remote attackers to send unlimited credential-guessing requests to specific routes like /dav, /.well-known, and /feeds. This bypasses the instance's anti-brute-force protections and can compromise accounts that rely only on passwords.

Detection Guidance

Check for excessive failed login attempts or unusual traffic patterns targeting /dav, /.well-known, or /feeds routes. Monitor logs for repeated credential-guessing requests against Vikunja endpoints.

Impact Analysis

If you use Vikunja before 2.6.0, attackers could exploit this to gain unauthorized access to your account by guessing passwords without being blocked by rate limits. This could lead to data theft, unauthorized modifications, or loss of control over your Vikunja instance.

Compliance Impact

This vulnerability could lead to unauthorized access to sensitive data, violating confidentiality requirements in GDPR and HIPAA. Organizations using affected Vikunja versions may face compliance breaches, potential fines, and reputational damage due to inadequate access controls.

Mitigation Strategies

Upgrade Vikunja to version 2.6.0 or later. Implement rate limiting on CalDAV BasicAuth endpoints. Disable BasicAuth if possible and enforce stronger authentication methods.

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