Update js-yaml to patched 4.3.0

[Copilot]

js-yaml@4.2.0 is vulnerable to quadratic CPU consumption when parsing chained YAML merge keys (CVE-2026-59869). Version 4.3.0 limits merged keys per parse.

• Dependency update

  • Pin the npm override to js-yaml@4.3.0.
  • Refresh the lockfile resolution and integrity hash.

• Reachability assessment — Not reachable (high confidence)

  • js-yaml is development-only and transitive through Jest coverage tooling.
  • Repository code does not import js-yaml or call load, loadAll, or YAML11_SCHEMA.
  • This update addresses dependency scanning rather than an active application exposure.

• Dependency resolution note

  • A standard npm refresh encounters the existing ts-jest@29.4.6 requirement for TypeScript <6 while the project declares TypeScript 6.
  • The lockfile was refreshed while preserving the existing peer dependency graph.

Original prompt

---

This section details the Dependabot vulnerability alert you should resolve

<alert_title>js-yaml: YAML merge-key chains can force quadratic CPU consumption</alert_title>
<alert_description>### Impact

js-yaml can spend quadratic CPU time parsing a document whose size grows only linearly. The issue is triggered by a chain of mappings where each mapping merges the previous one:

a0: &a0 { k0: 0 }
a1: &a1 { <<: *a0, k1: 1 }
a2: &a2 { <<: *a1, k2: 2 }
a3: &a3 { <<: *a2, k3: 3 }
...
b: *aN

For each new mapping, the loader has to enumerate the keys inherited from the previous mapping. With N chained mappings, this results in roughly 1 + 2 + ... + N merged-key visits, i.e., O(N^2) work for O(N) input size.

PoC

From N = 4000 delay become > 1s (doc size < 100K)

import { performance } from 'node:perf_hooks'
import { Buffer } from 'node:buffer'
import { load, YAML11_SCHEMA } from 'js-yaml'

const n = Number(process.argv[2] || 4000)

function makeMergeChain (count) {
  const lines = ['a0: &a0 { k0: 0 }']

  for (let i = 1; i < count; i++) {
    lines.push(`a${i}: &a${i} { <<: *a${i - 1}, k${i}: ${i} }`)
  }

  lines.push(`b: *a${count - 1}`)
  return `${lines.join('\n')}\n`
}

const source = makeMergeChain(n)

console.log(source.split('\n').slice(0, 8).join('\n'))
console.log('...')
console.log(source.split('\n').slice(-4).join('\n'))
console.log()
console.log(`N: ${n}`)
console.log(`YAML size: ${Buffer.byteLength(source)} bytes`)

const started = performance.now()
const result = load(source, { schema: YAML11_SCHEMA })
const elapsed = performance.now() - started

console.log(`parse time: ${elapsed.toFixed(1)} ms`)
console.log(`top-level keys: ${Object.keys(result).length}`)
console.log(`b keys: ${Object.keys(result.b).length}`)

Patches

Fix released. The most robust protection is to limit the total number of merged keys per parse call. This should close all past and future edge cases with merge. The default 10K-key limit should be okay in most cases.</alert_description>

high
GHSA-52cp-r559-cp3m, CVE-2026-59869
js-yaml
npm
<vulnerable_versions>4.2.0</vulnerable_versions>
<patched_version>4.3.0</patched_version>
<manifest_path>package-lock.json</manifest_path>

https://github.com/nodeca/js-yaml/security/advisories/GHSA-52cp-r559-cp3m https://nvd.nist.gov/vuln/detail/CVE-2026-59869 https://github.com/nodeca/js-yaml/commit/24f13e79ee1343a7e30bd6f6c9d9cdbf0ac9b2b7 https://github.com/nodeca/js-yaml/commit/59423c6f8cdc78742ac00e25a4dd39ef16b702e4 https://github.com/nodeca/js-yaml/releases/tag/3.15.0 https://github.com/nodeca/js-yaml/releases/tag/4.3.0 https://github.com/advisories/GHSA-52cp-r559-cp3m

<task_instructions>Resolve this alert by updating the affected package to a non-vulnerable version. Prefer the lowest non-vulnerable version (see the patched_version field above) over the latest to minimize breaking changes. Include a Reachability Assessment section in the PR description. Review the alert_description field to understand which APIs, features, or configurations are affected, then search the codebase for usage of those specific items. If the vulnerable code path is reachable, explain how (which files, APIs, or call sites use the affected functionality) and note that the codebase is actively exposed to this vulnerability. If the vulnerable code path is not reachable, explain why (e.g. the affected API is never called, the vulnerable configuration is not used) and note that the update is primarily to satisfy vulnerability scanners rather than to address an active risk. If the advisory is too vague to determine reachability (e.g. 'improper input validation' with no specific API named), state that reachability could not be determined and explain why. Include a confidence level in the reachability assessment (e.g. high confidence if the advisory names a specific API and you confirmed it is or is not called, low confidence if the usage is indirect and hard to trace). If no patched version is available, check the alert_description field for a Workarounds section — the advisory may describe configuration changes or usage patterns that mitigate the vulnerability without a version update. If a workaround is available, apply it and leave a code comment referencing the advisory identifier explaining it is a temporary mitigation. If neither a patch nor a workaround is available, explain in the PR description why the alert cannot be resolved automatically so a human reviewer can take over. Inspect the repository to determine which package manager is used (e.g. lock files, config files, build scripts) and use that tooling to perform the update — do not edit lock files directly. If the version constraint in the manifest (e.g. package.json, Gemfile, pyproject.toml) caps the version below the fi...

• Resolves github/copilot-release-notes alert #23

[Copilot]

Pull request overview

Updates the development-only js-yaml dependency to the patched version addressing CVE-2026-59869.

Changes:

• Pins the override to js-yaml@4.3.0.
• Refreshes the lockfile resolution and integrity hash.

Show a summary per file

File	Description
package.json	Pins the patched dependency version.
package-lock.json	Records the updated package artifact.

Review details

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• Files reviewed: 1/2 changed files
• Comments generated: 0
• Review effort level: Balanced

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