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CVE-2026-21881

Kanboard authentication bypass

9.1 CRITICALPublic exploitEPSS 0.49%
  1. Published8 Jan 2026

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.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityNone
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Affected products

Kanboard< 1.2.49

Remediation

Fixed in
Kanboard≥ 1.2.49

References

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Frequently asked

Is CVE-2026-21881 being actively exploited?

CVE-2026-21881 is not in the CISA KEV catalog. A public exploit reference exists, so treat it as exploitable. Its EPSS exploit probability is 0.49%.

How severe is CVE-2026-21881?

CVE-2026-21881 has a CVSS 3.1 base score of 9.1, rated critical. EPSS estimates a 0.49% probability of exploitation.

Which products are affected by CVE-2026-21881?

Affected products include Kanboard.

How do I fix CVE-2026-21881?

Upgrade affected software to a fixed version, for example Kanboard 1.2.49 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-21881 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.