CVE-2026-53666: CWE-470: Use of Externally-Controlled Input to Select Classes or Code ('Unsafe Reflection') in remix-run react-router
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.
AI Analysis
Technical Summary
CVE-2026-53666 describes an unsafe reflection vulnerability (CWE-470) in remix-run's react-router versions 6.4.0 through 7.17.0. If application code allows attacker-supplied input to overwrite certain error aspects during SSR, an attacker can cause unexpected constructor execution on the client side, resulting in outbound network requests. This vulnerability only affects applications using Framework Mode or Data Mode with manual SSR/hydration, not those using Declarative Mode. The vulnerability is resolved in react-router version 7.18.0.
Potential Impact
An attacker can exploit this vulnerability to trigger unexpected client-side constructor execution, causing outbound network requests. This could lead to information disclosure or other client-side impacts. The impact is limited to applications using Framework Mode or Data Mode with manual SSR/hydration and is not exploitable in Declarative Mode applications.
Mitigation Recommendations
Upgrade react-router to version 7.18.0 or later, where this vulnerability is fixed. If upgrading is not immediately possible, avoid using Framework Mode or Data Mode with manual SSR/hydration in a way that allows attacker-controlled input to overwrite error aspects. Applications using Declarative Mode are not affected and require no action.
CVE-2026-53666: CWE-470: Use of Externally-Controlled Input to Select Classes or Code ('Unsafe Reflection') in remix-run react-router
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 v3.1
Score 6.1medium
Affected software
remix-run
react-router
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-53666 describes an unsafe reflection vulnerability (CWE-470) in remix-run's react-router versions 6.4.0 through 7.17.0. If application code allows attacker-supplied input to overwrite certain error aspects during SSR, an attacker can cause unexpected constructor execution on the client side, resulting in outbound network requests. This vulnerability only affects applications using Framework Mode or Data Mode with manual SSR/hydration, not those using Declarative Mode. The vulnerability is resolved in react-router version 7.18.0.
Potential Impact
An attacker can exploit this vulnerability to trigger unexpected client-side constructor execution, causing outbound network requests. This could lead to information disclosure or other client-side impacts. The impact is limited to applications using Framework Mode or Data Mode with manual SSR/hydration and is not exploitable in Declarative Mode applications.
Mitigation Recommendations
Upgrade react-router to version 7.18.0 or later, where this vulnerability is fixed. If upgrading is not immediately possible, avoid using Framework Mode or Data Mode with manual SSR/hydration in a way that allows attacker-controlled input to overwrite error aspects. Applications using Declarative Mode are not affected and require no action.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-06-09T20:50:36.877Z
- Cvss Version
- 3.1
- State
- PUBLISHED
Threat ID: 6a67cc2f9c2644c7f8dbb228
Added to database: 07/27/2026, 21:22:55 UTC
Last enriched: 07/29/2026, 23:46:52 UTC
Last updated: 09/10/2026, 20:01:52 UTC
Views: 100
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