Can this vulnerability be exploited remotely over the internet?

Yes, if the Kanboard instance is reachable over the network and `REVERSE_PROXY_AUTH` is enabled without strict network or reverse-proxy controls, an attacker can send crafted HTTP requests from anywhere they can reach the service.

Does an attacker need valid credentials to exploit this issue?

No. The attacker does not need existing credentials; they only need the ability to send HTTP requests with spoofed authentication headers, which Kanboard then misinterprets as a legitimate login.

What is the safest general fix pattern for this kind of vulnerability?

The safest pattern is to ensure that authentication decisions are based on data that the application can fully trust. This often means validating tokens or credentials directly, or strictly verifying that any header-based identity information comes from a known, trusted reverse proxy and cannot be set by end users.

Severity:

CRITICAL RISK

(9.1)

Authentication Bypass via Untrusted Reverse Proxy Headers (CWE-287) in Kanboard

CVE-2026-21881

Published:

Jan 7, 2026

Status:

Analyzed

Summary

Affected Context

Exploit Preconditions

Why This Happens

Potential Impact

General Mitigation Guidance

How Teams Detect Issues Like This

Frequently Asked Questions

Source

NDV

Recent Vulnerabilities

CWE-306

CRITICAL RISK

CRITICAL

(9.8)

Missing Authentication for Forgot-Password Email Change API (CWE-306)

Account Takeover / Loss of Account Control

February 17, 2026

CWE-77;CWE-78

HIGH RISK

HIGH

(7.3)

OS Command Injection (CWE-78) in node-sonos-http-api TTS Provider for macOS

Remote Code Execution on the Server Host

February 17, 2026

Vulnerability Type

Category:

Authentication Bypass

CWE:

CWE-287

Impact:

Full Account Takeover and Privilege Escalation

Severity:

CRITICAL RISK

(9.1)

CVSS Version:

3.1

Vulnerability Type

Category:

Authentication Bypass

CWE:

CWE-287

Impact:

Full Account Takeover and Privilege Escalation

Severity:

CRITICAL RISK

(9.1)

CVSS Version:

3.1

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355 Bryant St. San Francisco, CA 94107, USA

Ask AI for summary of CodeAnt

Authentication Bypass via Untrusted Reverse Proxy Headers (CWE-287) in Kanboard

Summary

Affected Context

Exploit Preconditions

Why This Happens

Potential Impact

General Mitigation Guidance

How Teams Detect Issues Like This

Frequently Asked Questions

Source

Recent Vulnerabilities

CRITICAL RISK

CRITICAL

(9.8)

Missing Authentication for Forgot-Password Email Change API (CWE-306)

HIGH RISK

HIGH

(7.3)

OS Command Injection (CWE-78) in node-sonos-http-api TTS Provider for macOS

Vulnerability Type

Vulnerability Type

Vulnerability Type

Vulnerability Type

Catch This CVE While Code Is Being Written

Ship clean & secure code faster

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