Vulnerability · Published Jan 8, 2026 · Assigned by GitHub_M
CVE-2026-21881Kanboard is Vulnerable to Reverse Proxy Authentication Bypass
Critical 9.1
In plain English
A critical-severity improper authentication in kanboard from kanboard. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 42% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:14 | kanboard | 1.2.49+ds-1 | DEBIAN-CVE-2026-21881 |
Affected products (as reported)
Weakness: CWE-287 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N