4.3

CVSS Score

3.1

-

CVSS Score

Basic Information

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CVE-2025-62595

CVE-2025-62595: Koa Vulnerable to Open Redirect via Trailing Double-Slash (//) in back Redirect Logic

Koa is expressive middleware for Node.js using ES2017 async functions. In versions 2.16.2 to before 2.16.3 and 3.0.1 to before 3.0.3, a bypass to CVE-2025-8129 was discovered in the Koa.js framework affecting its back redirect functionality. In certain circumstances, an attacker can manipulate the Referer header to force a user’s browser to navigate to an external, potentially malicious website. This occurs because the implementation incorrectly treats some specially crafted URLs as safe relative paths. Exploiting this vulnerability could allow attackers to perform phishing, social engineering, or other redirect-based attacks on users of affected applications. This issue has been patched in version 3.0.3.

(GitHub Advisory)

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CVE-2025-62595

CVE-2025-62595:

4.3

CVSS Score

3.1

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
koa	npm	>= 3.0.1, < 3.0.3	3.0.3
koa	npm	>= 2.16.2, < 2.16.3	2.16.3

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability analysis began by examining the provided commit 769fd75cc6b30d72493b370b5a3ae2332ca03c5b, which was identified as the patch for the open redirect issue in Koa. The commit modified lib/response.js. The key change was the removal of a code block within the back function. This removed block checked if the Referrer header started with / and, if so, performed a redirect, assuming it was a safe relative path. The vulnerability description and the test case added in __tests__/response/back.test.js confirm that this logic was flawed because protocol-relative URLs (e.g., //evil.com) also start with / but are interpreted by browsers as external URLs. By removing this check, the patch ensures that all referrer URLs are properly parsed and their origin is validated against the application's host, thus closing the open redirect vulnerability. The vulnerable function is therefore back in lib/response.js, as it contained the logic that processed the malicious Referrer header and triggered the unsafe redirect.

Vulnerable functions

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WAF Protection Rules

WAF Rule

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Reasoning

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