CVE-2026-9520: Blitz Cross-Site Scripting Vulnerability

LOW
Advisory Identifier: GHSA-h2p9-cr4h-px24
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CVSS 4.3
CWE-79
Published
Advisory Summary

CVE-2026-9520 is a LOW (CVSS 4.3) cross-site scripting vulnerability (CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')) affecting Blitz libraries in the npm ecosystem. The issue involves blitz has a cross-site scripting issue. Remediation is available in the latest vendor maintenance releases.

CVE-2026-9520 at a Glance

CVE Identifier CVE-2026-9520
GHSA Identifier GHSA-h2p9-cr4h-px24
Severity LOW
CVSS v3.1 Base Score 4.3
CWE Classification CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Affected Product Blitz
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 4.3

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:R/S:U/C:N/I:L/A:N).

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

How to Fix CVE-2026-9520

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

blitz fixed: Latest secure release 
npm install blitz@Latest secure release
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 blitz

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-9520, inspect your project dependencies using npm:

npm ls blitz

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

Note: The npm ls blitz 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-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting'), where the product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. In Blitz, 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 weakness has been identified in blitz-js blitz up to 3.0.2 on GitHub. This impacts an unknown function of the file packages/generator/templates/app/src/app/auth/components/LoginForm.tsx of the component Sign-in. This manipulation of the argument Next causes cross site scripting. It is possible to initiate the attack remotely. The exploit has been made available to the public and could be used for attacks. The vendor was contacted early about this disclosure but did not respond in any way.

CVE-2026-9520 Affected Blitz Versions

1 component(s)
Product / Package Ecosystem Affected Versions Fixed Version
blitz
npm/blitz
npm
≤ 3.0.2

References

NVD — CVE-2026-9520 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-9520
Blitz Source Repository REPOSITORY
https://gist.github.com/TrebledJ/164c7ca6c8208b63e6937bc11984720b
Blitz Source Repository REPOSITORY
https://github.com/blitz-js/blitz
vuldb.com/submit/814378 WEB
https://vuldb.com/submit/814378
vuldb.com/vuln/365540 WEB
https://vuldb.com/vuln/365540
vuldb.com/vuln/365540/cti WEB
https://vuldb.com/vuln/365540/cti

Frequently Asked Questions

What is CVE-2026-9520?
CVE-2026-9520 is a security vulnerability in Blitz involving Blitz has a Cross-site Scripting issue under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting').
Which Blitz versions are affected?
Affected versions include releases prior to current release patches across affected packages: blitz.
What version fixes CVE-2026-9520?
Upgrading to current release patches (or the latest patched release for your respective branch) resolves the vulnerability.
Is blitz affected?
Yes, blitz is affected in releases prior to Latest secure release. Upgrade your dependency to Latest secure release or later.
What is the CVSS score of CVE-2026-9520?
CVE-2026-9520 has a CVSS v3.1 base score of 4.3 (LOW) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N.
What CWE is associated with CVE-2026-9520?
CVE-2026-9520 is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.).
How can I check npm dependencies for CVE-2026-9520?
Run the dependency tree command: 'npm ls blitz'. 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-h2p9-cr4h-px24",
  "modified" : "2026-06-30T17:39:56Z",
  "published" : "2026-05-26T13:30:53Z",
  "aliases" : [ "CVE-2026-9520" ],
  "summary" : "Blitz has a Cross-site Scripting issue",
  "details" : "A weakness has been identified in blitz-js blitz up to 3.0.2 on GitHub. This impacts an unknown function of the file packages/generator/templates/app/src/app/auth/components/LoginForm.tsx of the component Sign-in. This manipulation of the argument Next causes cross site scripting. It is possible to initiate the attack remotely. The exploit has been made available to the public and could be used for attacks. The vendor was contacted early about this disclosure but did not respond in any way.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "blitz"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "3.0.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-9520"
  }, {
    "type" : "WEB",
    "url" : "https://gist.github.com/TrebledJ/164c7ca6c8208b63e6937bc11984720b"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/blitz-js/blitz"
  }, {
    "type" : "WEB",
    "url" : "https://vuldb.com/submit/814378"
  }, {
    "type" : "WEB",
    "url" : "https://vuldb.com/vuln/365540"
  }, {
    "type" : "WEB",
    "url" : "https://vuldb.com/vuln/365540/cti"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-30T17:39:56Z",
    "nvd_published_at" : "2026-05-26T02:16:40Z"
  }
}