Auth bypass in Kanboard
CVE-2026-21881
Kanboard is project management software focused on Kanban methodology. Versions 1.2.48 and below is vulnerable to a critical authentication bypass when REVERSE_PROXY_AUTH is enabled. The application blindly trusts HTTP headers for user authentication without verifying the request originated from a trusted reverse proxy. An attacker can impersonate any user, including administrators, by simply sending a spoofed HTTP header. This issue is fixed in version 1.2.49.
Vulnerability class: Broken Authentication
EPSS: 0.004 (35.5th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 9.1 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N.
Affected products
- Kanboard — versions < 1.2.49
Weakness classification (CWE)
References
- security-advisories@github.com (x_refsource_CONFIRM, Exploit, Vendor Advisory)
- security-advisories@github.com (Patch, x_refsource_MISC)
- security-advisories@github.com (x_refsource_MISC, Release Notes)
Frequently asked questions
- What is CVE-2026-21881?
- CVE-2026-21881 is a critical-severity vulnerability in Kanboard, classified under Improper Authentication. CVSS score: 9.1/10. Published 2026-01-08.
- How severe is CVE-2026-21881?
- Critical severity. CVSS v3 base score is 9.1 out of 10.