Is this vulnerability remotely exploitable?

Yes. An attacker who can send HTTP requests to the affected Koa application can exploit the issue by crafting malicious Host headers, assuming the application uses `ctx.hostname` in a vulnerable way.

Does exploitation require authentication or special privileges?

Typically no. Host headers are part of the HTTP request and can usually be controlled by any remote client. Authentication is only required if the vulnerable code path (for example, password reset or email verification) is gated behind authenticated flows, but the header itself remains attacker-controlled.

What is the safest general fix pattern?

The safest pattern is to stop treating `ctx.hostname` as authoritative. Use a trusted, configured application base URL for all security-sensitive link generation, apply strict hostname validation and allowlisting where host-based logic is unavoidable, and ensure malformed Host headers are rejected at the edge.

Severity:

HIGH RISK

(7.5)

Improper Host Header Validation (CWE-20) in Koa ctx.hostname API

CVE-2026-27959

Published:

Feb 25, 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

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Vulnerability Type

Category:

Improper Input Validation

CWE:

CWE-20

Impact:

Host Header Injection leading to spoofed URLs, poisoned links, and security control bypass

Severity:

HIGH RISK

(7.5)

CVSS Version:

3.1

Vulnerability Type

Category:

Improper Input Validation

CWE:

CWE-20

Impact:

Host Header Injection leading to spoofed URLs, poisoned links, and security control bypass

Severity:

HIGH RISK

(7.5)

CVSS Version:

3.1

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Improper Host Header Validation (CWE-20) in Koa ctx.hostname API

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

(9.9)

Command Injection in MCP Stdio Configuration Validation (CWE-78) in WeKnora

CRITICAL RISK

CRITICAL

(9.9)

SQL Injection via PostgreSQL Array/Row Expressions (CWE-89) in WeKnora Query Engine

Vulnerability Type

Vulnerability Type

Vulnerability Type

Catch This CVE While Code Is Being Written

Ship clean & secure code faster

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