# CVE-2025-62595: Koa open redirect via protocol-relative URLs in back redirect

Source: https://junglewise.ai/threats/cve-2025-62595-koa-open-redirect-via-protocol-relative-urls-in-back-redirect  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2025-10-21. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2025-62595 · Severity: medium · CVSS 4.3 · Published 2025-10-21

Koa is a popular Node.js web framework that handles HTTP requests and responses for web applications. The framework's back redirect feature contains a flaw that allows attackers to craft malicious referer headers to redirect users to attacker-controlled websites. An attacker could use this to execute phishing attacks or steal user credentials by making users visit fake login pages.

Technologies: [koa (npm)](https://junglewise.ai/threats/technologies/npm-koa). Vendors: [npm](https://junglewise.ai/threats/vendors/npm).

## Quick answers

**Is CVE-2025-62595 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2025-62595 being exploited in the wild.

**How severe is CVE-2025-62595?** Medium severity, with a CVSS score of 4.3, published 21 October 2025.

**Which products and versions are affected?** koa (npm) SEMVER:introduced=3.0.1,fixed=3.0.3.

**Is there a fix for CVE-2025-62595?** Yes. koa (npm): upgrade to 3.0.3 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2025-62595 attacked?** It is attacked over the network.

**Am I affected by CVE-2025-62595?** Check whether you run koa (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- koa (npm): upgrade to 3.0.3 or later

  ```sh
  npm install koa@3.0.3
  ```


## Technical details

The vulnerability is an open redirect (CWE-601) in Koa's response.redirect() implementation, specifically in the back redirect logic in response.js line 326. The code checks if a referrer URL starts with "/" to treat it as a safe relative path, but protocol-relative URLs like "//evil.com" also start with "/" and are passed through unchecked. When a browser receives "Location: //evil.com", it interprets this as a redirect to https://evil.com, bypassing the intended same-origin protection. An attacker can craft a request with "Referer: //attacker.com" to trigger a cross-origin redirect. User interaction is required (the user must click a crafted link). Patches are available in Koa 2.16.3 and 3.0.3.

## Affected products

- Koa Koa 2.16.2 through 2.16.2; 3.0.1 through 3.0.2

## Identifiers

- CVE-2025-62595
- GHSA-g8mr-fgfg-5qpc

## Timeline

- 2025-10-21: disclosed: Advisory published
- 2025-10-21: patched: Patches released in versions 2.16.3 and 3.0.3

## References

- [https://github.com/koajs/koa/security/advisories/GHSA-g8mr-fgfg-5qpc](https://github.com/koajs/koa/security/advisories/GHSA-g8mr-fgfg-5qpc)

## Related threats

- [Koa Host header injection in ctx.hostname API](https://junglewise.ai/threats/cve-2026-27959-koa-host-header-injection-in-ctx-hostname-api)
- [Koa open redirect via referrer header](https://junglewise.ai/threats/cve-2025-8129-koa-open-redirect-via-referrer-header)