CVE-2026-53666

Received Received - Intake

React Router Constructor Execution via SSR Error Handling

Publication date: 2026-07-27

Last updated on: 2026-07-27

Assigner: GitHub, Inc.

Description

React Router is a router for React. In versions 6.4.0 through 7.17.0, if application code was written in a way that allows attacker-supplied input to overwrite certain aspects of errors caught by the SSR process, then it was possible for an attacker to trigger unexpected constructor execution on the client, which would in turn trigger an outbound network request. This is only possible with very specific (and unlikely) application-layer code. Note that this does not impact an application if it is using Declarative Mode. It only impacts Framework Mode and Data Mode applications that perform manual SSR/hydration. This issue has been fixed in version 7.18.0.

CVSS Scores

EPSS Scores

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Meta Information

Published

2026-07-27

Last Modified

2026-07-27

Generated

2026-07-28

AI Q&A

2026-07-28

EPSS Evaluated

N/A

NVD

CVE-2026-53666

Affected Vendors & Products

Vendor	Product	Version / Range
react_router	react_router	From 6.4.0 (inc) to 7.17.0 (inc)
react_router	react_router	7.18.0

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-470	The product uses external input with reflection to select which classes or code to use, but it does not sufficiently prevent the input from selecting improper classes or code.

Attack-Flow Graph

Executive Summary

This vulnerability affects React Router versions 6.4.0 through 7.17.0. If attacker-controlled input overwrites certain error aspects during server-side rendering (SSR), it could trigger unexpected constructor execution on the client. This leads to an outbound network request. Only specific application code patterns are vulnerable, and it does not impact Declarative Mode. Framework Mode and Data Mode apps using manual SSR/hydration are affected.

Detection Guidance

Detection requires checking if your React Router version is between 6.4.0 and 7.17.0. Run: npm list react-router or yarn list react-router. If the version falls in this range, the system is potentially vulnerable.

Impact Analysis

An attacker could exploit this to make unauthorized outbound network requests from your application. This may lead to data exfiltration or interaction with malicious servers. The impact is limited to specific code patterns and only affects certain React Router modes.

Compliance Impact

This vulnerability could potentially violate compliance requirements by enabling unauthorized data transmission. GDPR and HIPAA require protecting data integrity and confidentiality. Exploitation may lead to unauthorized network requests, risking data breaches or leaks.

Mitigation Strategies

Upgrade React Router to version 7.18.0 or later immediately. This can be done via npm update react-router or yarn upgrade react-router. Verify the update with the same commands used for detection.

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