CVE-2026-21881

published 2026-01-08

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…

Priority P2 67 critical 9.1 CVSS 3.1

AV N AC L PR N UI N S U C H I H A N

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

3 ranges

Vendor	Product	Version range	Fixed in
debian	kanboard	< kanboard 1.2.49+ds-1 (forky)	kanboard 1.2.49+ds-1 (forky)
kanboard	kanboard	< 1.2.49	1.2.49
kanboard	kanboard	>= 0 < 1.2.49+ds-1	1.2.49+ds-1

Detection & IOCs extracted from sources · hover to see the quote

• → Authentication bypass via spoofed HTTP header when REVERSE_PROXY_AUTH is enabled in Kanboard; monitor for requests containing reverse-proxy authentication headers (e.g., REMOTE_USER or X-Forwarded-User) originating from untrusted/non-proxy source IPs ↗
• → Flag Kanboard instances running versions 1.2.48 and below with REVERSE_PROXY_AUTH enabled as actively exploitable; prioritize upgrade to 1.2.49 ↗

• · Vulnerability is only exploitable when REVERSE_PROXY_AUTH is explicitly enabled in the Kanboard configuration; instances without this feature enabled are not affected ↗

CVSS provenance

nvd v3.1 9.1 CRITICAL CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

osv 9.1 CRITICAL

vendor_debian 9.1 CRITICAL

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