CVE-2026-53666Network attack vector

Client-side network requests via unrestricted error constructors

Published Jul 27, 2026 · Updated Jul 27, 2026

Unsafe reflection in React Router 6.4.0 through 7.17.0 allows remote attackers to trigger client-side constructor execution during SSR hydration. The deserializeErrors() path reads an attacker-influenced __subType value and resolves window[__subType] as an Error constructor without restricting the name to supported error classes. Exploitation requires user interaction and narrowly written application code that lets input overwrite SSR-caught error data; only Framework Mode or Data Mode applications with manual SSR/hydration are affected, and the observed consequence is an outbound browser request.

CVSS severity6.1
Medium
EPSS probability0.30%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Unsafe reflection in React Router 6.4.0 through 7.17.0 allows remote attackers to trigger client-side constructor execution during SSR hydration. The deserializeErrors() path reads an attacker-influenced __subType value and resolves window[__subType] as an Error constructor without restricting the name to supported error classes. Exploitation requires user interaction and narrowly written application code that lets input overwrite SSR-caught error data; only Framework Mode or Data Mode applications with manual SSR/hydration are affected, and the observed consequence is an outbound browser request.

The record

CVE
CVE-2026-53666
Published
Jul 27, 2026
Updated
Jul 27, 2026
Vendor
Shopify
Product
React Router
Classifications
CWE-470
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 27, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 27, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 6.4.0, < 7.18.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Shopify · React Routerversion=>= 6.4.0, < 7.18.0

Published CVSS scores

6.1GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-470Use of Externally-Controlled Input to Select Classes or Code ('Unsafe Reflection')

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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