How severe is CVE-2026-21881?

CVE-2026-21881 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.

Is CVE-2026-21881 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (35th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-21881?

CVE-2026-21881 affects Kanboard. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-21881?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

Does CVE-2026-21881 have an EU (EUVD) identifier?

Yes. CVE-2026-21881 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-1668.

When was CVE-2026-21881 published?

CVE-2026-21881 was published on 2026-01-08 and last updated on 2026-06-17.

CVE-2026-21881

CVE-2026-21881 is a critical-severity vulnerability in Kanboard with a CVSS 3.x base score of 9.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-287.

Key facts

Severity: Critical (CVSS 3.x base score 9.1)
EPSS exploit prediction: 0% (35th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-1668
Weakness: CWE-287
Affected product: Kanboard
Published: 2026-01-08
Last modified: 2026-06-17

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.

Frequently asked questions

What is 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.
How severe is CVE-2026-21881?: CVE-2026-21881 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.
Is CVE-2026-21881 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (35th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-21881?: CVE-2026-21881 affects Kanboard. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-21881?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
Does CVE-2026-21881 have an EU (EUVD) identifier?: Yes. CVE-2026-21881 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-1668.
When was CVE-2026-21881 published?: CVE-2026-21881 was published on 2026-01-08 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:kanboard:kanboard:*:*:*:*:*:*:*:*

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