CVE-2026-34077: React router Denial of Service Vulnerability

HIGH
Advisory Identifier: GHSA-rxv8-25v2-qmq8
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CVSS 7.5
CWE-770
Published
Advisory Summary

CVE-2026-34077 is a HIGH (CVSS 7.5) denial of service vulnerability (CWE-770: Allocation of Resources Without Limits or Throttling) affecting React router libraries in the npm ecosystem. The issue involves react router vulnerable to denial of service via reflected user input in single-fetch. Remediation is available by upgrading affected packages to version 7.14.0, 3.0.0.

CVE-2026-34077 at a Glance

CVE Identifier CVE-2026-34077
GHSA Identifier GHSA-rxv8-25v2-qmq8
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-770: Allocation of Resources Without Limits or Throttling
Affected Product React router
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 7.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity None (I:N)
Availability High (A:H)

How to Fix CVE-2026-34077

To remediate this vulnerability, upgrade all affected React router dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

react-router fixed: 7.14.0 
npm install react-router@7.14.0
turbo-stream fixed: 3.0.0 
npm install turbo-stream@3.0.0
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

npm ls react-router

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-34077, inspect your project dependencies using npm:

npm ls react-router

Analyze the terminal output to locate any version of React router in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 7.14.0), your application is affected.

Note: The npm ls react-router command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-770: Allocation of Resources Without Limits or Throttling, where the product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated. In React router, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

A DoS vulnerability exists in the React Router v7 [Framework Mode](https://reactrouter.com/start/modes#framework), as well as Remix v2.9.0+ with [Single Fetch](https://v2.remix.run/docs/guides/single-fetch) enabled. In some scenarios the underlying serialization algorithm can become a bottleneck when encoding specific types of data into server responses. Please upgrade to React Router v7.14.0 or later. > [!NOTE] > This does not impact your React Router application if you are using [Declarative Mode](https://reactrouter.com/start/modes#declarative) (`<BrowserRouter>`) or [Data Mode](https://reactrouter.com/start/modes#data) (`createBrowserRouter`/`<RouterProvider>`).

CVE-2026-34077 Affected React router Versions

2 component(s)
Fixed Versions:
7.14.03.0.0
Product / Package Ecosystem Affected Versions Fixed Version
react-router
npm/react-router
npm
≥ 7.0.0
< 7.14.0
7.14.0
turbo-stream
npm/turbo-stream
npm
< 3.0.0
3.0.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/remix-run/react-router/security/advisories/GHSA-rxv8-25v2-qmq8
NVD — CVE-2026-34077 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-34077
Security Fix Commit FIX COMMIT
https://github.com/remix-run/react-router/commit/59811921d3c7d599077b8cadccdcd65a233165e0
React router Source Repository REPOSITORY
https://github.com/jacob-ebey/turbo-stream/blob/v2.4.1/src/flatten.ts#L175-L177
React router Source Repository REPOSITORY
https://github.com/jacob-ebey/turbo-stream/blob/v2.4.1/src/unflatten.ts#L185-L189
React router Source Repository REPOSITORY
https://github.com/remix-run/react-router

Frequently Asked Questions

What is CVE-2026-34077?
CVE-2026-34077 is a security vulnerability in React router involving React Router vulnerable to Denial of Service via reflected user input in single-fetch under CWE-770: Allocation of Resources Without Limits or Throttling.
Which React router versions are affected?
Affected versions include releases prior to 7.14.0, 3.0.0 across affected packages: react-router, turbo-stream.
What version fixes CVE-2026-34077?
Upgrading to 7.14.0, 3.0.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is react-router affected?
Yes, react-router is affected in releases prior to 7.14.0. Upgrade your dependency to 7.14.0 or later.
Is turbo-stream affected?
Yes, turbo-stream is affected in releases prior to 3.0.0. Upgrade your dependency to 3.0.0 or later.
What is the CVSS score of CVE-2026-34077?
CVE-2026-34077 has a CVSS v3.1 base score of 7.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
What CWE is associated with CVE-2026-34077?
CVE-2026-34077 is classified under CWE-770: Allocation of Resources Without Limits or Throttling (The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.).
How can I check npm dependencies for CVE-2026-34077?
Run the dependency tree command: 'npm ls react-router'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-rxv8-25v2-qmq8",
  "modified" : "2026-06-04T15:23:51Z",
  "published" : "2026-06-04T15:23:51Z",
  "aliases" : [ "CVE-2026-34077" ],
  "summary" : "React Router vulnerable to Denial of Service via reflected user input in single-fetch",
  "details" : "A DoS vulnerability exists in the React Router v7 [Framework Mode](https://reactrouter.com/start/modes#framework), as well as Remix v2.9.0+ with [Single Fetch](https://v2.remix.run/docs/guides/single-fetch) enabled. In some scenarios the underlying serialization algorithm can become a bottleneck when encoding specific types of data into server responses.  Please upgrade to React Router v7.14.0 or later.\n\n> [!NOTE]\n> This does not impact your React Router application if you are using [Declarative Mode](https://reactrouter.com/start/modes#declarative) (`<BrowserRouter>`) or [Data Mode](https://reactrouter.com/start/modes#data) (`createBrowserRouter`/`<RouterProvider>`).",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "react-router"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "7.0.0"
      }, {
        "fixed" : "7.14.0"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "turbo-stream"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "3.0.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/remix-run/react-router/security/advisories/GHSA-rxv8-25v2-qmq8"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-34077"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/remix-run/react-router/commit/59811921d3c7d599077b8cadccdcd65a233165e0"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/jacob-ebey/turbo-stream/blob/v2.4.1/src/flatten.ts#L175-L177"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/jacob-ebey/turbo-stream/blob/v2.4.1/src/unflatten.ts#L185-L189"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/remix-run/react-router"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-770" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-04T15:23:51Z",
    "nvd_published_at" : "2026-06-02T20:16:34Z"
  }
}