CVE-2026-6594: @brikcss/merge Deep Merge Is Vulnerable To Vulnerability

MODERATE
Advisory Identifier: GHSA-3jc6-6r48-v6qf
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CVSS 7.3
CWE-1321 CWE-94
Published
Advisory Summary

CVE-2026-6594 is a MODERATE (CVSS 7.3) deep merge is vulnerable to vulnerability (CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')) affecting @brikcss/merge libraries in the npm ecosystem. The issue involves deep merge is vulnerable to prototype pollution through lack of sanitization. Remediation is available in the latest vendor maintenance releases.

CVE-2026-6594 at a Glance

CVE Identifier CVE-2026-6594
GHSA Identifier GHSA-3jc6-6r48-v6qf
Severity MODERATE
CVSS v3.1 Base Score 7.3
CWE Classification CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
Affected Product @brikcss/merge
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 7.3

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

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 Low (C:L)
Integrity Low (I:L)
Availability Low (A:L)

How to Fix CVE-2026-6594

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

@brikcss/merge fixed: Latest secure release 
npm install @brikcss/merge@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 @brikcss/merge

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-6594, inspect your project dependencies using npm:

npm ls @brikcss/merge

Analyze the terminal output to locate any version of @brikcss/merge 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 @brikcss/merge 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-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution'), where the product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype. In @brikcss/merge, 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 Prototype Pollution vulnerability was determined in brikcss merge up to 1.3.0. Executing a manipulation of the argument __proto__/constructor.prototype/prototype can lead to improperly controlled modification of object prototype attributes. The attack may be performed from remote. The vendor was contacted early about this disclosure but did not respond in any way.

CVE-2026-6594 Affected @brikcss/merge Versions

1 component(s)
Product / Package Ecosystem Affected Versions Fixed Version
@brikcss/merge
npm/@brikcss/merge
npm
≤ 1.3.1

References

NVD — CVE-2026-6594 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-6594
@brikcss/merge Source Repository REPOSITORY
https://github.com/brikcss/merge
@brikcss/merge Source Repository REPOSITORY
https://github.com/sudo-secure/security-research/blob/main/brikcss-merge/prototype-pollution/PoC.md
vuldb.com/submit/791805 WEB
https://vuldb.com/submit/791805
vuldb.com/vuln/358229 WEB
https://vuldb.com/vuln/358229
vuldb.com/vuln/358229/cti WEB
https://vuldb.com/vuln/358229/cti

Frequently Asked Questions

What is CVE-2026-6594?
CVE-2026-6594 is a security vulnerability in @brikcss/merge involving Deep Merge is Vulnerable to Prototype Pollution Through Lack of Sanitization under CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution').
Which @brikcss/merge versions are affected?
Affected versions include releases prior to current release patches across affected packages: @brikcss/merge.
What version fixes CVE-2026-6594?
Upgrading to current release patches (or the latest patched release for your respective branch) resolves the vulnerability.
Is @brikcss/merge affected?
Yes, @brikcss/merge 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-2026-6594?
CVE-2026-6594 has a CVSS v3.1 base score of 7.3 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L.
What CWE is associated with CVE-2026-6594?
CVE-2026-6594 is classified under CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution') (The product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype.).
How can I check npm dependencies for CVE-2026-6594?
Run the dependency tree command: 'npm ls @brikcss/merge'. 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-3jc6-6r48-v6qf",
  "modified" : "2026-04-23T14:23:26Z",
  "published" : "2026-04-20T03:34:41Z",
  "aliases" : [ "CVE-2026-6594" ],
  "summary" : "Deep Merge is Vulnerable to Prototype Pollution Through Lack of Sanitization",
  "details" : "A Prototype Pollution vulnerability was determined in brikcss merge up to 1.3.0. Executing a manipulation of the argument __proto__/constructor.prototype/prototype can lead to improperly controlled modification of object prototype attributes. The attack may be performed from remote. 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:N/S:U/C:L/I:L/A:L"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@brikcss/merge"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "1.3.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-6594"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/brikcss/merge"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/sudo-secure/security-research/blob/main/brikcss-merge/prototype-pollution/PoC.md"
  }, {
    "type" : "WEB",
    "url" : "https://vuldb.com/submit/791805"
  }, {
    "type" : "WEB",
    "url" : "https://vuldb.com/vuln/358229"
  }, {
    "type" : "WEB",
    "url" : "https://vuldb.com/vuln/358229/cti"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1321", "CWE-94" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-23T14:23:26Z",
    "nvd_published_at" : "2026-04-20T02:16:15Z"
  }
}