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
Published · last modified .
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.
EPSS exploit prediction
EPSS: 0.005 (39.9th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 40th percentile — 39.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.005 · change: +0.000
Affected products
- Kanboard — versions < 1.2.49
Weakness classification (CWE)
References
- github.com/kanboard/kanboard/security/advisories/GHSA-wwpf-3j4p-739w (Exploit, Vendor Advisory)
- github.com/kanboard/kanboard/commit/7af6143e2ad25b5c15549cca8af4341c7ac4e2fc (Patch)
- github.com/kanboard/kanboard/releases/tag/v1.2.49 (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.