# CVE-2025-43864: React Router DoS via cache poisoning by forcing SPA mode

Source: https://junglewise.ai/threats/cve-2025-43864-react-router-dos-via-cache-poisoning-by-forcing-spa-mode  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2025-04-24. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2025-43864 · Severity: low · CVSS 3.1 · Published 2025-04-24

React Router is a popular routing library used to build web applications. An attacker can exploit a vulnerability by adding a custom HTTP header to requests, which forces the framework into single-page application (SPA) mode and triggers an error on server-rendered applications. If the response is cached, this error gets served to all subsequent users, causing widespread service disruption and preventing legitimate users from accessing the application.

Technologies: [React-Router](https://junglewise.ai/threats/technologies/npm-react-router).

## Quick answers

**Is CVE-2025-43864 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2025-43864 being exploited in the wild.

**How severe is CVE-2025-43864?** Low severity, with a CVSS score of 3.1, published 24 April 2025.

**Which products and versions are affected?** React-Router SEMVER:introduced=7.2.0,fixed=7.5.2.

**Is there a fix for CVE-2025-43864?** Yes. React-Router: upgrade to 7.5.2 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2025-43864 attacked?** It is attacked over the network.

**Am I affected by CVE-2025-43864?** Check whether you run React-Router 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

- React-Router: upgrade to 7.5.2 or later

## Technical details

The vulnerability exists in React Router's Framework mode when a page uses a loader. By injecting the X-React-Router-SPA-Mode header into requests, an attacker can force the application to operate in SPA mode when it is configured for server-side rendering (SSR). This mismatch triggers an unhandled error that corrupts the response content. The attack vector is network-based with no authentication, privileges, or user interaction required. If a caching layer (CDN, reverse proxy, or HTTP cache) is in place, the poisoned error response becomes cached and served to all users, resulting in persistent denial of service. The vulnerability affects React Router versions 7.2.0 through 7.5.1 and is fixed in version 7.5.2.

## Affected products

- Remix React Router 7.2.0 through 7.5.1

## Identifiers

- CVE-2025-43864
- GHSA-f46r-rw29-r322

## Timeline

- 2025-04-24: disclosed: Advisory published
- 2025-04-24: patched: Fixed in React Router 7.5.2

## References

- [https://github.com/remix-run/react-router/security/advisories/GHSA-f46r-rw29-r322](https://github.com/remix-run/react-router/security/advisories/GHSA-f46r-rw29-r322)

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