# Koa open redirect via Referrer header

Source: https://junglewise.ai/threats/koa-open-redirect-via-referrer-header-0a2cc61b  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2025-07-25. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

Severity: low · CVSS 3.1 · Published 2025-07-25

Koa is a popular Node.js web framework used to build web applications and APIs. A vulnerability in Koa's redirect functionality allows an attacker to redirect users to arbitrary external websites by crafting a request with a malicious Referrer header. An attacker could exploit this to conduct phishing attacks, credential theft, or spread malware by tricking users into visiting attacker-controlled sites.

Technologies: [Koajs Koa](https://junglewise.ai/threats/technologies/koa). Vendors: [Koajs](https://junglewise.ai/threats/vendors/koajs).

## Quick answers

**Is This vulnerability exploited in the wild?** No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.

**How severe is This vulnerability?** Low severity, with a CVSS score of 3.1, published 25 July 2025.

**Which products and versions are affected?** Koajs Koa up to 3.0.0.

**Is there a fix for This vulnerability?** A patch was published on 2025: Fixed in version 3.0.1 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is This vulnerability attacked?** It is attacked over the network, in a software library.

**Am I affected?** Check whether you run Koajs Koa 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.

## Technical details

The vulnerability is an open redirect (CWE-601) in the `back()` method of Koa's HTTP response handler (lib/response.js). The method uses the user-controlled Referrer header to determine the redirect target without validation, allowing an attacker to specify an arbitrary URL. The attack is network-accessible and requires minimal preconditions: an attacker sends a request with a malicious Referrer header to a route using `ctx.redirect('back')`. The vulnerability affects Koa versions up to 3.0.0 and is fixed in version 3.0.1.

## Affected products

- KoaJS Koa up to 3.0.0

## Timeline

- 2025-07-08: disclosed
- 2025-07-25: advisory
- 2025-07-29: other: Advisory withdrawn as duplicate of GHSA-jgmv-j7ww-jx2x
- 2025: patched: Fixed in version 3.0.1

## References

- [https://github.com/koajs/koa/issues/1892](https://github.com/koajs/koa/issues/1892)

## Related threats

- [Koajs Cross-Site Scripting in ctx.redirect()](https://junglewise.ai/threats/cve-2025-32379-koajs-cross-site-scripting-in-ctx-redirect)
- [Koa inefficient regular expression in header parsing](https://junglewise.ai/threats/cve-2025-25200-koa-inefficient-regular-expression-in-header-parsing)