[WIP] Fix js-yaml maxTotalMergeKeys CPU consumption vulnerability

[Copilot]

• Inspect the dependency graph and affected js-yaml call sites
• Update every js-yaml 3.15.1 lock entry to 3.15.2 using npm
• Verify lockfile scope, resolved versions, and dependency installation
• Run final automated review and security validation

Reachability Assessment

Repository tooling and GitHub workflow code parse YAML with js-yaml load APIs, and the affected transitive dependencies are used by validation tooling (@azure/openapi-markdown, front-matter, and json-refs). YAML merge processing is enabled by default in js-yaml 3.x, so crafted YAML processed through these dependencies can reach the vulnerable empty-merge-source path. The codebase is therefore actively exposed to this CPU-exhaustion vulnerability. Confidence: medium, because YAML parsing is confirmed but the affected calls are indirect through transitive packages.

Validation

• npm ci passed using the repository's documented temporary public-registry substitution for the sandbox-only private-feed DNS failure; the committed lockfile was restored afterward.
• npm ls js-yaml --all confirms all affected paths resolve to 3.15.2.
• Direct merge-budget probes against each installed 3.15.2 copy confirm empty merge sources are rejected when maxTotalMergeKeys is exceeded.
• No js-yaml 3.15.1 entries remain in package-lock.json.
• Secret scan passed.
• Automated review reported no findings; CodeQL skipped the lockfile-only metadata change as trivial.
• npm audit still reports pre-existing advisories, including the separately resolved js-yaml 4.3.1 node, which is outside this alert's explicit 3.15.1-to-3.15.2 scope.

Original prompt

---

This section details the Dependabot vulnerability alert you should resolve

<alert_title>js-yaml: maxTotalMergeKeys does not limit CPU use for empty merge sources</alert_title>
<alert_description>## 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

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

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.</alert_description>

high
GHSA-2883-xcg3-v3hh, CVE-2026-84375
js-yaml
npm
<vulnerable_versions>3.15.1</vulnerable_versions>
<patched_version>3.15.2</patched_version>
<manifest_path>package-lock.json</manifest_path>

https://github.com/nodeca/js-yaml/security/advisories/GHSA-2883-xcg3-v3hh https://nvd.nist.gov/vuln/detail/CVE-2026-84375 https://github.com/nodeca/js-yaml/pull/797 https://github.com/nodeca/js-yaml/commit/3485bc06ff8a0251505f44a00414d90df2466639 https://github.com/nodeca/js-yaml/commit/6a8e05f9a485188ed730ac81e81ae221352ef480 https://github.com/nodeca/js-yaml/commit/d90b6612a5a84385bdcb556c44578eac76dc0f6b https://github.com/nodeca/js-yaml/releases/tag/3.15.2 https://github.com/nodeca/js-yaml/releases/tag/4.3.2 https://github.com/advisories/GHSA-2883-xcg3-v3hh

<agent_instructions>Bump all instances of js-yaml to 3.15.2. Only update package-lock.json.</agent_instructions>

<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 fix, update the constraint first. For transitive dependencies, determine whether it is simpler to update the direct dependency that pulls in the vulnerable package or to update the transitive dependency directly, and choose...

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