CVE-2026-21881 Kanboard is Vulnerable to Reverse Proxy Authentication Bypass
Attackers can impersonate any user, including administrators, by spoofing HTTP headers when reverse proxy authentication is enabled.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-21881?
CVE-2026-21881 is a critical authentication bypass vulnerability in kanboard, published on 8 Jan 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Weakness: CWE-287
Which versions are affected by CVE-2026-21881?
It affects 1 product.
Products include Kanboard Kanboard.
How do I fix CVE-2026-21881?
No fix has been published for CVE-2026-21881 yet. Limit exposure of the affected software until one is available.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-21881 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-21881 exists.
Other vulnerabilities in kanboard
- CVE-2025-55010 Kanboard Authenticated Admin Remote Code Execution via Unsafe Deserialization of Events
- CVE-2024-51747 Arbitrary File Read and Delete in kanboard
- CVE-2024-51748 Remote code execution through language setting in kanboard
- CVE-2017-12850 Business logic in n/a
- CVE-2017-12851 Business logic in n/a
Sources
Also known as GHSA-wwpf-3j4p-739w.