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Full vulnerability report · 2026
CVE-2026-53666High confidence

React Router: Arbitrary Constructor Injection via deserializeErrors() in React Router SSR Hydration

remix-run · react-router

Official source article: GitHub GHSA-337J-9HXR-RHXG ↗. Check the applicable product and release in the original source.

6.1MediumCVSS 3.1
Recommended action
Patch only the product branches with a verified fix

Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority. Verified remediation exists for at least one product or source, but 155 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Fix availability varies by product
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityMediumOperational priority:Medium, unchanged from published severity.unchanged

Evidence used

  • No CISA KEV confirmation is currently recorded.
  • EPSS is 0.42% for the current model date.

Compensating controls

  • Validate the affected product branch and deploy the verified fixed release.
  • Restrict the affected network interface to trusted sources where business-safe.
  • Monitor vendor guidance and exploitation sources for a material change.

Verification

  1. Confirm that the asset runs remix-run react-router and falls inside the recorded affected range.
  2. Verify the installed build against the product-specific fixed version after deployment.
  3. Validate exposure, authentication requirements and compensating controls in the actual environment.
  4. Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Mitigation target: As exposure requiresRemediation target: Within 365 days

This automated reassessment organises public evidence. It does not know asset exposure, business impact or control effectiveness and does not replace CVSS or a human risk decision.

Cross-source reconciliation

Remediation availability differs by product scope

Verified remediation exists for at least one product or source, but 155 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Open-source package ranges2 source-attributed ranges

These OSV and GitHub advisory ranges apply only to the named package and ecosystem. A listed fixed version is not a universal product patch or proof that an update is installed.

Ecosystem and packageAffected rangeFirst fixed versionEvidence
npmreact-router>= 6.4.0, < 7.18.07.18.0GitHub advisory ↗upstream repository advisory · 23 Jul 2026
npmreact-routerSEMVER: introduced 6.4.0; fixed 7.18.07.18.0OSV record ↗aggregator derived · 10 Sep 2026
Direct vendor intelligence

Authoritative vendor CSAF and VEX advisories

Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.

1 current
CVE-2026-53666 · CSAF 2.0 · revision 3 · finalRed Hat Product Securityreact-router: React Router: Information disclosure via client-side constructor execution
155 known affected

The vendor explicitly identifies these products as affected by this CVE.

  • cryostat-openshift-console-plugin-npm as a component of Cryostat 4
  • grafana-infinity-datasource-npm as a component of Cryostat 4
  • react-router as a component of Cryostat 4
  • exploit-intelligence-tech-preview/agent-client-rhel9 as a component of Exploit Intelligence
  • gatekeeper/gatekeeper-rhel9 as a component of Gatekeeper 3
  • mta/mta-ui-rhel8 as a component of Migration Toolkit for Applications 8
  • mta/mta-ui-rhel9 as a component of Migration Toolkit for Applications 8
  • rhmtc/openshift-migration-ui-rhel8 as a component of Migration Toolkit for Containers
  • migration-toolkit-virtualization/mtv-console-plugin-rhel9 as a component of Migration Toolkit for Virtualization
  • multicluster-engine/console-mce-rhel9 as a component of Multicluster Engine for Kubernetes
  • network-observability/network-observability-console-plugin-pf4-rhel9 as a component of Network Observability Operator
  • network-observability/network-observability-console-plugin-pf5-rhel9 as a component of Network Observability Operator
Summary
A flaw was found in React Router. If an application is configured to allow attacker-supplied input to modify errors during server-side rendering (SSR), a remote attacker could trigger unexpected code execution on the client. This execution could lead to an outbound network request, potentially resulting in limited information disclosure or unintended network activity. This vulnerability specifically affects applications utilizing Framework Mode and Data Mode with manual SSR/hydration.
Remediation
To mitigate this issue, ensure that custom application code does not permit attacker-controlled input to modify error objects during server-side rendering (SSR) when using React Router in Framework or Data Modes. Review and harden application-layer error handling to prevent such overwrites. Applications not requiring Framework or Data Mode SSR should consider utilizing Declarative Mode, which is unaffected.
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2026-49628

No EUVD known-exploited evidence

ENISA has published the identifier mapping but no EUVD description has been stored yet.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
Not supplied in the stored EUVD record
Advisory evidence
No linked advisory details stored yet
Recommended actionPatch only the product branches with a verified fix

Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority. Verified remediation exists for at least one product or source, but 155 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Fix availability varies by product
01

What, why and how

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.

What

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.

Why

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.

How

An attacker operating through a network path may attempt exploitation without authentication after a user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

What

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.

Why

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.

How

An attacker operating through a network path may attempt exploitation without authentication after a user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path
a network path → Use of Externally-Controlled Input to Select Classes or Code ('Unsafe Reflection') → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
Required interaction required
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Changed: exploitation can affect a different security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-470 ↗

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

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRNonePrivileges required: The attacker does not need an account or existing privileges.UIRequiredUser interaction: Another user must perform an action for exploitation to succeed.SChangedScope: The attack can affect a component governed by a different security authority.CLowConfidentiality impact: A successful attack can cause a limited loss.ILowIntegrity impact: A successful attack can cause a limited loss.ANoneAvailability impact: No direct loss is represented by this metric.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkUnauthenticatedCWE-470
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

Cyber Security Agency of Singapore · English · CSA-SB-20260729Security Bulletin 29 Jul 2026

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 29 Jul 2026, published on 29 July 2026. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
CERT-FR · French · CERTFR-2026-AVI-1233Multiples vulnérabilités dans les produits IBM

ord?id=CVE-2026-47057 Référence CVE CVE-2026-47058 https://www.cve.org/CVERecord?id=CVE-2026-47058 Référence CVE CVE-2026-47059 https://www.cve.org/CVERecord?id=CVE-2026-47059 Référence CVE CVE-2026-47063 https://www.cve.org/CVERecord?id=CVE-2026-47063 Référence CVE CVE-2026-4873 https://www.cve.org/CVERecord?id=CVE-2026-4873 Référence CVE CVE-2026-48779 https://www.cve.org/CVERecord?id=CVE-2026-48779 Référence CVE CVE-2026-49356 https://www.cve.org/CVERecord?id=CVE-2026-49356 Référence CVE CVE-2026-49875 https://www.cve.org/CVERecord?id=CVE-2026-49875 Référence CVE CVE-2026-53550 https://www.cve.org/CVERecord?id=CVE-2026-53550 Référence CVE CVE-2026-53666 https://www.cve.org/CVERecord?id=CVE-2026-53666 Référence CVE CVE-2026-53668 https://www.cve.org/CVERecord?id=CVE-2026-53668 Référence CVE CVE-2026-53669 https://www.cve.org/CVERecord?id=CVE-2026-53669 Référence CVE CVE-2026-55602 https://www.cve.org/CVERecord?id=CVE-2026-55602 Référence CVE CVE-2026-55603 https://www.cve.org/CVERecord?id=CVE-2026-55603 Référence CVE CVE-2026-58059 https://www.cve.org/CVERecord?id=CVE-2026-58059 Référence CVE CVE-2026-58060 https://www.cve.org/CVERecord?id=CVE-2026-58060 Référence CVE CVE-2026-58061 https://www.cve.org/CVERecord?id=CVE-2026-58061 Référence CVE CVE-2026-58062 https://www.cve.org/CVERecord?id=

Official advisory ↗
CERT-FR · French · CERTFR-2026-AVI-1165Multiples vulnérabilités dans les produits IBM

d?id=CVE-2026-50162 Référence CVE CVE-2026-50163 https://www.cve.org/CVERecord?id=CVE-2026-50163 Référence CVE CVE-2026-50169 https://www.cve.org/CVERecord?id=CVE-2026-50169 Référence CVE CVE-2026-50184 https://www.cve.org/CVERecord?id=CVE-2026-50184 Référence CVE CVE-2026-50557 https://www.cve.org/CVERecord?id=CVE-2026-50557 Référence CVE CVE-2026-50560 https://www.cve.org/CVERecord?id=CVE-2026-50560 Référence CVE CVE-2026-50645 https://www.cve.org/CVERecord?id=CVE-2026-50645 Référence CVE CVE-2026-52746 https://www.cve.org/CVERecord?id=CVE-2026-52746 Référence CVE CVE-2026-53434 https://www.cve.org/CVERecord?id=CVE-2026-53434 Référence CVE CVE-2026-53666 https://www.cve.org/CVERecord?id=CVE-2026-53666 Référence CVE CVE-2026-53668 https://www.cve.org/CVERecord?id=CVE-2026-53668 Référence CVE CVE-2026-53669 https://www.cve.org/CVERecord?id=CVE-2026-53669 Référence CVE CVE-2026-54171 https://www.cve.org/CVERecord?id=CVE-2026-54171 Référence CVE CVE-2026-54225 https://www.cve.org/CVERecord?id=CVE-2026-54225 Référence CVE CVE-2026-54264 https://www.cve.org/CVERecord?id=CVE-2026-54264 Référence CVE CVE-2026-54265 https://www.cve.org/CVERecord?id=CVE-2026-54265 Référence CVE CVE-2026-54284 https://www.cve.org/CVERecord?id=CVE-2026-54284 Référence CVE CVE-2026-54297 https://www.cve.org/CVERecord?id=

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2026-026756ShopifyのReact Routerにおけるクラスまたはコードを選択する外部から制御された入力の使用に関する脆弱性

React RouterはReact用のルーターです。バージョン6.4.0から7.17.0の間では、アプリケーションコードが攻撃者から提供された入力によってSSRプロセスで捕捉されたエラーの特定部分を上書きできるように記述されていた場合、攻撃者はクライアント上で予期しないコンストラクターを実行させることが可能でした。これにより、外向きのネットワーク要求がトリガーされる可能性があります。ただし、これは非常に特異かつ可能性の低いアプリケーション層コードでのみ発生する問題です。宣言型モードを使用しているアプリケーションには影響しません。影響を受けるのは手動でSSRやハイドレーションを行うフレームワークモードおよびデータモードのアプリケーションのみです。この問題はバージョン7.18.0で修正されました。

Official advisory ↗
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Fix availability varies by product
Affected
Fixed
7.18.0.
Action
Use the product-specific evidence above. Patch only products with a verified fixed release, and keep every affected or under-investigation state without a matching fix in the remediation queue.
Workaround
To mitigate this issue, ensure that custom application code does not permit attacker-controlled input to modify error objects during server-side rendering (SSR) when using React Router in Framework or Data Modes. Review and harden application-layer error handling to prevent such overwrites. Applications not requiring Framework or Data Mode SSR should consider utilizing Declarative Mode, which is unaffected.
04

Evidence and provenance

Published 27 Jul 2026 · Last source change 28 Jul 2026, 15:19 UTC · CWE-470 · Use of Externally-Controlled Input to Select Classes or Code ('Unsafe Reflection')

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2026-49628
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD enriched

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates ↗
  1. Affected versionsThe structured affected or fixed version information changed.
    Before
    cryostat-openshift-console-plugin-npm as a component of Cryostat 4; grafana-infinity-datasource-npm as a component of Cryostat 4; react-router as a component of Cryostat 4; exploit-intelligence-tech-preview/agent-client-rhel9 as a component of Exploit Intelligence; gatekeeper/gatekeeper-rhel9 as a component of Gatekeeper 3; mta/mta-ui-rhel8 as a component of Migration Toolkit for Applications 8; mta/mta-ui-rhel9 as a component of Migration Toolkit for Applications 8; rhmtc/openshift-migration-ui-rhel8 as a component of Migration Toolkit for Containers; migration-toolkit-virtualization/mtv-console-plugin-rhel9 as a component of Migration Toolkit for Virtualization; multicluster-engine/console-mce-rhel9 as a component of Multicluster Engine for Kubernetes; network-observability/network-observability-console-plugin-pf4-rhel9 as a component of Network Observability Operator; network-observability/network-observability-console-plugin-pf5-rhel9 as a component of Network Observability Operator; network-observability/network-observability-console-plugin-rhel9 as a component of Network Observability Operator; workload-availability/node-healthcheck-must-gather-rhel9 as a component of Node HealthCheck Operator; workload-availability/node-healthcheck-operator-bundle as a component of Node HealthCheck Operator; workload-availability/node-healthcheck-rhel9-operator as a component of Node HealthCheck Operator; openshift-lightspeed/lightspeed-agentic-console-rhel9 as a component of OpenShift Lightspeed; openshift-lightspeed/lightspeed-console-plugin-419-rhel9 as a component of OpenShift Lightspeed; openshift-lightspeed/lightspeed-console-plugin-pf5-rhel9 as a component of OpenShift Lightspeed; openshift-lightspeed/lightspeed-console-plugin-rhel9 as a component of OpenShift Lightspeed; openshift-pipelines/pipelines-console-plugin-pf5-rhel9 as a component of OpenShift Pipelines; openshift-pipelines/pipelines-console-plugin-rhel8 as a component of OpenShift Pipelines; openshift-pipelines/pipelines-console-plugin-rhel9 as a component of OpenShift Pipelines; openshift-pipelines/pipelines-hub-ui-rhel8 as a component of OpenShift Pipelines; openshift-pipelines/pipelines-hub-ui-rhel9 as a component of OpenShift Pipelines; openshift-service-mesh/kiali-operator-bundle as a component of OpenShift Service Mesh 3; openshift-service-mesh/kiali-ossmc-rhel9 as a component of OpenShift Service Mesh 3; openshift-service-mesh/kiali-rhel9 as a component of OpenShift Service Mesh 3; openshift-service-mesh/kiali-rhel9-operator as a component of OpenShift Service Mesh 3; rhacm2/console-rhel9 as a component of Red Hat Advanced Cluster Management for Kubernetes 2; and 126 more
    After
    cryostat-openshift-console-plugin-npm as a component of Cryostat 4; grafana-infinity-datasource-npm as a component of Cryostat 4; react-router as a component of Cryostat 4; exploit-intelligence-tech-preview/agent-client-rhel9 as a component of Exploit Intelligence; gatekeeper/gatekeeper-rhel9 as a component of Gatekeeper 3; mta/mta-ui-rhel8 as a component of Migration Toolkit for Applications 8; mta/mta-ui-rhel9 as a component of Migration Toolkit for Applications 8; rhmtc/openshift-migration-ui-rhel8 as a component of Migration Toolkit for Containers; migration-toolkit-virtualization/mtv-console-plugin-rhel9 as a component of Migration Toolkit for Virtualization; multicluster-engine/console-mce-rhel9 as a component of Multicluster Engine for Kubernetes; network-observability/network-observability-console-plugin-pf4-rhel9 as a component of Network Observability Operator; network-observability/network-observability-console-plugin-pf5-rhel9 as a component of Network Observability Operator; network-observability/network-observability-console-plugin-rhel9 as a component of Network Observability Operator; workload-availability/node-healthcheck-must-gather-rhel9 as a component of Node HealthCheck Operator; workload-availability/node-healthcheck-operator-bundle as a component of Node HealthCheck Operator; workload-availability/node-healthcheck-rhel9-operator as a component of Node HealthCheck Operator; openshift-lightspeed/lightspeed-agentic-console-rhel9 as a component of OpenShift Lightspeed; openshift-lightspeed/lightspeed-console-plugin-419-rhel9 as a component of OpenShift Lightspeed; openshift-lightspeed/lightspeed-console-plugin-pf5-rhel9 as a component of OpenShift Lightspeed; openshift-lightspeed/lightspeed-console-plugin-rhel9 as a component of OpenShift Lightspeed; openshift-pipelines/pipelines-console-plugin-pf5-rhel9 as a component of OpenShift Pipelines; openshift-pipelines/pipelines-console-plugin-rhel8 as a component of OpenShift Pipelines; openshift-pipelines/pipelines-console-plugin-rhel9 as a component of OpenShift Pipelines; openshift-pipelines/pipelines-hub-ui-rhel8 as a component of OpenShift Pipelines; openshift-pipelines/pipelines-hub-ui-rhel9 as a component of OpenShift Pipelines; openshift-service-mesh/kiali-operator-bundle as a component of OpenShift Service Mesh 3; openshift-service-mesh/kiali-ossmc-rhel9 as a component of OpenShift Service Mesh 3; openshift-service-mesh/kiali-rhel9 as a component of OpenShift Service Mesh 3; openshift-service-mesh/kiali-rhel9-operator as a component of OpenShift Service Mesh 3; rhacm2/console-rhel9 as a component of Red Hat Advanced Cluster Management for Kubernetes 2; and 125 more
    Red Hat Product Security ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release or patch reference recorded
ENISA EUVD · EUVD-2026-49628↗Vendor CSAF · Red Hat Product Security↗Patch or update reference↗Patch or update reference↗CVE authority or vendor reference · GitHub GHSA-337J-9HXR-RHXG↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2026-53666 · cve.blacktree.nl