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Kanboard CVE-2026-21881

CRITICAL
Improper Authentication (CWE-287)
2026-01-08 security-advisories@github.com
Authentication Bypass Kanboard
9.1
CVSS 3.1 · GitHub Advisory
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Severity by source

GitHub Advisory PRIMARY
9.1 CRITICAL
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Primary rating from GitHub Advisory · only source for this CVE.

CVSS VectorGitHub Advisory

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

Lifecycle Timeline

4
Analysis Generated
Mar 12, 2026 - 21:54 vuln.today
PoC Detected
Jan 20, 2026 - 15:57 vuln.today
Public exploit code
Patch released
Jan 20, 2026 - 15:57 nvd
Patch available
CVE Published
Jan 08, 2026 - 02:15 nvd
CRITICAL 9.1

DescriptionGitHub Advisory

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.

AnalysisAI

Kanboard project management (through 1.2.48) has an authentication bypass when REVERSE_PROXY_AUTH is enabled. The application trusts HTTP headers for authentication without verifying the request came from the reverse proxy. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Send crafted HTTP request with spoofed user header
Exploit
Application trusts header without proxy validation
Execution
Attacker authenticated as arbitrary user
Impact
Access admin functions and data
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Vulnerability AssessmentAI

Exploitation REVERSE_PROXY_AUTH configuration option must be enabled in Kanboard versions 1.2.48 and below. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment CVSS 9.1 (Critical). … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker sends a request directly to Kanboard (bypassing the reverse proxy) with the header X-Forwarded-User: admin. Kanboard accepts this as authenticated admin access, granting full project management control.
Remediation Update to the patched version. … Detailed patch versions, workarounds, and compensating controls in full report.
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Recommended ActionAI

Within 24 hours: Identify all affected systems and apply vendor patches immediately. …

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CVE-2026-21881 vulnerability details – vuln.today
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