CVE-2026-73643: js-yaml Denial of Service Vulnerability

HIGH
Advisory Identifier: GHSA-pm4m-ph32-ghv5
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CVSS 7.5
CWE-407
Published
Advisory Summary

CVE-2026-73643 is a HIGH (CVSS 7.5) denial of service vulnerability (CWE-407: Inefficient Algorithmic Complexity) affecting js-yaml libraries in the npm ecosystem. The issue involves exponential parsing time in flow collections leads to denial of service. Remediation is available by upgrading affected packages to version 5.2.2.

CVE-2026-73643 at a Glance

CVE Identifier CVE-2026-73643
GHSA Identifier GHSA-pm4m-ph32-ghv5
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-407: Inefficient Algorithmic Complexity
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-2026-73643

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: 5.2.2 
npm install js-yaml@5.2.2
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-2026-73643, 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 5.2.2), 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-407: Inefficient Algorithmic Complexity, where an algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached. 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 Parsing a small YAML document can take exponential time. An application that calls `load()` or `loadAll()` on untrusted input can be hung by a payload under 200 bytes. ### Details When an entry in a flow sequence turns out to be a `key: value` pair, the parser rewinds and parses that entry a second time as the key. If the key is itself a nested flow sequence of the same shape, every level is parsed twice, so the total work is O(2^n) in the nesting depth. The default `maxDepth` of 100 does not help, because the time is already unmanageable at about 30 to 40 levels. Root cause, potentially the: `readFlowCollection` in [parser.ts](https://github.com/nodeca/js-yaml/blob/master/src/parser/parser.ts), the `restoreState` followed by a second `parseNode` further down. ### PoC ```javascript const yaml = require('js-yaml') const n = 30 yaml.load('[ '.repeat(n) + '1' + ' ]: 0'.repeat(n)) ``` With default options: 22 levels takes about 1 second, 26 levels about 17 seconds, 30 levels over 2 minutes. The input stays under 200 bytes and grows linearly with `n`. ### Impact Denial of service. A single small request can keep one CPU busy for minutes or longer and blocks the Node event loop, so one request can stall the whole process. No anchors, aliases, merges, tags, or non default options are required, and it reproduces on the default schema.

CVE-2026-73643 Affected js-yaml Versions

1 component(s)
Fixed Versions:
5.2.2
Product / Package Ecosystem Affected Versions Fixed Version
js-yaml
npm/js-yaml
npm
≥ 5.0.0
< 5.2.2
5.2.2

References

GitHub Advisory / Wiki ADVISORY
https://github.com/nodeca/js-yaml/security/advisories/GHSA-pm4m-ph32-ghv5
Security Fix Commit FIX COMMIT
https://github.com/nodeca/js-yaml/commit/3e5240f9cbe645ce5afb58524954a13c8539c853
js-yaml Source Repository REPOSITORY
https://github.com/nodeca/js-yaml
js-yaml Release RELEASE
https://github.com/nodeca/js-yaml/releases/tag/5.2.2

Frequently Asked Questions

What is CVE-2026-73643?
CVE-2026-73643 is a security vulnerability in js-yaml involving Exponential parsing time in flow collections leads to denial of service under CWE-407: Inefficient Algorithmic Complexity.
Which js-yaml versions are affected?
Affected versions include releases prior to 5.2.2 across affected packages: js-yaml.
What version fixes CVE-2026-73643?
Upgrading to 5.2.2 (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 5.2.2. Upgrade your dependency to 5.2.2 or later.
What is the CVSS score of CVE-2026-73643?
CVE-2026-73643 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-2026-73643?
CVE-2026-73643 is classified under CWE-407: Inefficient Algorithmic Complexity (An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached.).
How can I check npm dependencies for CVE-2026-73643?
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-pm4m-ph32-ghv5",
  "modified" : "2026-08-13T17:47:36Z",
  "published" : "2026-07-24T16:47:36Z",
  "aliases" : [ "CVE-2026-73643" ],
  "summary" : "js-yaml: Exponential parsing time in flow collections leads to denial of service",
  "details" : "### Summary\nParsing a small YAML document can take exponential time. An application that calls `load()` or `loadAll()` on untrusted input can be hung by a payload under 200 bytes.\n\n### Details\nWhen an entry in a flow sequence turns out to be a `key: value` pair, the parser rewinds and parses that entry a second time as the key.\nIf the key is itself a nested flow sequence of the same shape, every level is parsed twice, so the total work is O(2^n) in the nesting depth. The default `maxDepth` of 100 does not help, because the time is already unmanageable at about 30 to 40 levels.\n\nRoot cause, potentially the: `readFlowCollection` in [parser.ts](https://github.com/nodeca/js-yaml/blob/master/src/parser/parser.ts), the `restoreState` followed by a second `parseNode` further down.\n\n\n### PoC\n\n```javascript\nconst yaml = require('js-yaml')\nconst n = 30\nyaml.load('[ '.repeat(n) + '1' + ' ]: 0'.repeat(n))\n```\n\nWith default options: 22 levels takes about 1 second, 26 levels about 17 seconds, 30 levels over 2 minutes. The input stays under 200 bytes and grows linearly with `n`.\n\n### Impact\nDenial of service. A single small request can keep one CPU busy for minutes or longer and blocks the Node event loop, so one request can stall the whole process. No anchors, aliases, merges, tags, or non default options are required, and it reproduces on the default schema.",
  "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" : "5.0.0"
      }, {
        "fixed" : "5.2.2"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 5.2.1"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/nodeca/js-yaml/security/advisories/GHSA-pm4m-ph32-ghv5"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nodeca/js-yaml/commit/3e5240f9cbe645ce5afb58524954a13c8539c853"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/nodeca/js-yaml"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nodeca/js-yaml/releases/tag/5.2.2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-407" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-24T16:47:36Z",
    "nvd_published_at" : null
  }
}